Chapter 5 

Population Studies of the Monoterpene 

Composition of 4- to 12-Year-Old 

Half Siblings of P. ponderosa 

Summary: The study included about 1,500 half-siblings, 4 to 12 years old, of 21 

P. ponderosa that were selected primarily on the basis of monoterpene 

composition. Three of the ecotypic regions (monoterpene races) of P. ponderosa 

were represented, and results were based on 25 to 200 siblings per parent. 

Composition of individual trees of a set of half-siblings usually varied greatly 

in two or more major components. Average composition of a set of progeny 

tended to be broadly intermediate between the parent tree and the average of 

the local stand. Parents with similar composition produced progeny with quite 

similar arrays of compositions and frequency distribution characteristics. 

However, limonene and myrcene were lower than the calculated intermediate 

amounts; α-pinene and ß-pinene were higher. A juvenile effect is postulated 

that was more or less evident in all young growth. The effect of this juvenile 

factor was much the same as that shown by plants under stress. Therefore, all 

young trees or young parts of older trees may be under some level of stress— 

the stress of rapid growth. Nearly one third of the half-siblings of a high 

limonene parent could be classed as high limonene or potentially so. Some 

high-limonene trees were found among the progeny of a parent that could be 

classed only as near-high limonene. A rare tree was found with ultra-high 

limonene, though such trees have not been found in mature, natural stands. 

There were some differences between the three geographic regions in the 

comparative ratios between parent and progeny for a given monoterpene, 

suggesting that the locality of a parent tree may have an effect on the juvenile 

response or that there were minor genetic effects that are distinctive to a region, 

or that there was an effect on a young tree grown far from its seed source. Two 

forms of stress—over-application of a phytocide and prolonged growth in a 

restrictive container—caused a sharp change in quantitative composition, 

usually evidenced by lower levels of limonene and myrcene and higher 

levels α-pinene and ß-pinene. Results, in general, indicated that the quickest 

and cheapest way to obtain trees with a diverse array of compositions was 

the use of wind-pollinated seed from localities with much variation in 

individual tree composition. 

Research on young half-sibling populations served three purposes: (1) to 

better understand natural populations; (2) to provide a readily available supply 

of trees with a diverse array of monoterpene compositions for research on host 

resistance, and for studies of monoterpene genetics; and (3) to guide the 

selection of parent trees for breeding programs and to make preliminary allele 

assignments for tree breeding studies. 

One of the conclusions of the extensive study of natural stands of P. 

ponderosa (Smith 1977) (see Chapter 3) was that there was evidence of two 

additive alleles at a single locus for each of the five major monoterpenes of 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 197 
Chapter 5 Populati

on Studies of the Monoterpene Composition Smith 

of 4-to 12-Year-Old Half Siblings of P. ponderosa 

P. ponderosa: α-pinene, ß-pinene, 3-carene, myrcene, and limonene. Parallel 

research strongly indicated that the different components of P. ponderosa xylem 

monoterpene differed in their toxicity to western pine beetle, a serious pest of 

P. ponderosa (Smith 1965). Then, field experiments demonstrated that lowered 

success of beetle attack could be related to the quantity of resin that exudes 

from a wound and to the quality of monoterpenes; beetle attack was less 

successful in the trees with the greatest flow of resin and the greatest amount of 

limonene (Smith 1975). 

These early studies showed the need for and desirability of breeding and 

population studies of the xylem monoterpenes of P. ponderosa. The types of 

composition obtained by various combinations of parent trees were of primary 

concern. Studies were conducted for this purpose from 1970 to 1980. Trees 

located by the range-wide study of P. ponderosa (see Chapter 3) were the source 

of the plant material. Parent trees were selected for the primary objective of 

getting different compositions, particularly high limonene, and therefore may 

not have been best suited for genetic studies. Nevertheless, the selection of 

parent trees seems to have been fortuitously adequate for genetic studies. Of 

course, in all breeding studies of P. ponderosa, cone production is often a strong 

factor in tree selection; the selected trees had to have cones the year of selection. 

The first bioassay of resistance to western pine beetle (Dendroctonus 

brevicomis), using trees developed from the seed collection and controlled pollination work, was conducted in 1982 but the results were inconclusive 

because the trees were too small—less than 2 inches in diameter—and most 

beetle attacks were abnormal. The next bioassay was conducted in 1987. By that 

time the trees were 8 to 12 years old and 2-3 inches in diameter. That size is still 

far below the minimum diameter that is attacked by western pine beetle, under 

natural conditions, 6 to 8 inches in diameter. Nevertheless, the tests were 

conducted. The results, as reported in Chapter 9, clearly showed that the 

degree of success of beetle attack was inversely related to limonene content and 

also inversely related to the quantity of resin exudation—although exudation 

rate does not seem to apply too strongly in very small trees (see Chapter 9). 

However, the results also clearly indicated that trees of this size, about 3 inches 

in diameter, were not well suited for this type of bioassay. More confident 

bioassay should be made when the trees are 6 to 8 inches in diameter. However, 

small trees seemed to be suitable for beetle bioassay on a comparative basis, 

and this could greatly shorten the time to evaluate results of breeding and plant 

selection. 

It would be helpful to introduce the subject of stress here because it became 

quite clear as population studies of very young trees progressed, that various 

forms of stress, or presumed stress, could markedly change the quantitative 

xylem monoterpene composition of trees less than 15 years old. Hodges and 

Lorio (1975) found no change in the xylem monoterpene composition of mature 

P. taeda that were put under experimental stress. They did find small changes in 

the composition of the resin acid. During the course of the studies reported, 

five sources of stress were found that markedly affected composition in very 

young trees: prolonged growth in restrictive containers, over application of a 

phytocide, great distance between parent trees, juvenile growth, and severe 

wounding. The first four sources of stress will be discussed within the various 

sections of this chapter; severe wounding will be discussed in Chapter 7 on 

grafts. In all cases, no matter what the type or source, stress was manifested by 

an increase in α-pinene and ß-pinene and sometimes 3-carene, and by a 

decrease in myrcene and limonene. In a recent comprehensive review of stress 

in human cells, Welch (1993) found that the reaction of the cell was always the 

same: increased production of the same group of chemicals, no matter what the mode or source of stress. Thus, there was a basic similarity between plants and 

animals in response to stress. 

198 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Two other factors might be involved separately or in conjunction with the 

five noted above. First, at times and under certain conditions not fully 

understood, it appeared that the type of composition itself may be an important 

factor in stress and juvenile reaction, and ß-pinene may be the component 

involved. This was a possible factor in the Ranger Peak progeny in particular 

and in the Wheeler Peak progeny to a lesser degree. Second, there were 

indications that the growth of the seedling well outside its seed zone may affect 

the level of activity of the previous factors. 

Selection of Parent Trees 

Parent trees for sibling studies were selected from two sources: trees previously 

noted in the extensive study of the regional and local variation of P. ponderosa 

xylem monoterpene (see Chapter 3, #14 of this volume), and a basic breeding 

tree, located at the Institute of Forest Genetics (IFG) near Placerville, California 

(fig. 5-1). 

The following sets of trees provided wind-pollinated seed—their 

compositions will be given in the appropriate section (fig. 5-1): 

1. four trees in the Ranger Peak locality on the Los Padres National Forest; 

2. 13 trees in the Wheeler Peak locality on the Humboldt National Forest 

(the location is now in the Great Basin National Park); 

3. two trees at the Adin Summit locality on the Modoc National Forest; 

4. one tree in the Camino Arboretum at IFG; this tree is a graft of one of 

the trees at Adin Summit. 

5. one tree on the Eldorado National Forest near IFG. 

Cones from all the trees were taken to IFG, and seeds were extracted and 

stored by the standard procedures used for all work with pines (Cumming and 

Righter 1948). 

Nursery and Plantation Practices 

Seeds were stratified for at least 30 days before sowing in early spring. Nursery 

beds were 5 ft. by 98 ft. In the 1971-1979 nurseries, seeds were spotted every 6 

in. in rows that were 6 in. apart. In the 1980-1982 nurseries, a 1-ft by 1-ft spacing 

was used and found to be much better for this type of work. The seeds in one 

row were always of the same source. The seeds for a given source in a nursery 

were usually in a single block of adjacent rows. Beds were irrigated for only the 

first 3 or 4 years. 

The beds were usually thinned first at 4 to 6 years by removing alternate 

plants or alternate rows. A second thinning was made at 6 to 8 years. 

Subsequent thinnings were made to provide the best spacing for the residual 

trees or to favor those trees which were considered most suitable for bioassay 

studies with western pine beetle. One bed was thinned more frequently to 

more accurately measure the possible effects of time of growth on composition. 

The trees were grown and examined in four types of areas at IFG as follows. 

1. Nursery: Seeds were planted and trees maintained in the nursery bed 

until examination. Nurseries were started each year from 1971 to 1982 except 

1973 and 1980. 

2. Plantation: One-year seedlings from the nursery bed were transplanted 

to a 6-ft by 6-ft plantation with nine half-siblings in a block as bare root stock in 

1978. The plantation was irrigated for 3 years. 

3. Containers: Seeds were planted in a container and were maintained 

there until trees were upscaled to larger containers. Two sets of containers were 

used. One set was started in 1978 and upscaled each year for 7 years from 1-in 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 199 
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-1—Locations in California and 

Nevada used in the study of half-sibling 

populations of P. ponderosa (●). 

200 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smi

th Population Studies of the Monoterpene Composition Chapter 5 

of 4-to 12-Year-Old Half Siblings of P. ponderosa 

by 6-in containers to 6-in by 18-in containers. The trees were then grown for 

two more years in these large containers. The other set was started in 1983 and 

upscaled for 3 years to 2-in by 10-in containers when they were examined. 

Containers were irrigated during all the growing season for all years. 

4. Container/Plantation: Seeds were planted in containers and upscaled as 

described above. The trees were transplanted to a plantation. Two sets of 

containers were used. One set was upscaled to 3-in by 6-in containers at the 

fourth year and then outplanted. The other set was upscaled 5 years to 6-in by 

18-in containers, held for 2 more years in these containers and then outplanted. 

The plantation and the container/plantation were treated with a phytocide 

early in spring of the first 3 years after planting. The second-year treatment of 

the phytocide was too heavy, and many trees were killed; the trees that survived 

showed reduced growth for a year or two. It is likely that the whole plantation 

was under moderate to severe stress for at least a year with the intensity of the 

stress apparently irregularly scattered throughout the plantation. By the time of the first sampling in 1987, virtually all trees were growing very well with 

internode length of 18 in. to 24 in. However, there may have been some residual 

effect of stress. 

Sampling for Resin 

All trees were sampled for xylem resin either by severing the tree when the 

nursery bed was thinned or by making a basal micro-tap as described in 

Chapter 2. 

Obtaining a sample of resin by the severing process was as follows. The tree 

was cut off about 6 in above the ground; this was usually within the first 

internode. The cut surface was scraped or cut clean with a razor blade. By 

waiting to do the scraping until a small amount of resin had exuded to the 

surface, the resin of the tree was acting as a de facto cleaning agent. If cortex 

resin was present, a ring of cortex about 0.25 in wide was cut from the top 

circumference of the small stump. This was done to prevent the mixing of 

xylem resin with the cortex resin. In general, trees less than 6 years old still 

have resin in the cortex at the base of the tree. Older trees usually do not have 

cortex resin in the basal internode, but this can vary by 2 to 4 years depending 

on rate of growth. In general, there will be no cortex resin where the bark has 

developed fissures and plates. Two to 4 hours or more after cutting and 

cleaning, sufficient resin for a sample would have exuded to the surface. A thin 

glass rod was moved across the surface to "pick up" a drop of resin. The rod 

with the drop of resin on the end was placed in a 2-cc screw-cap vial. When 10 

to 20 such vials had been obtained, they were taken to the laboratory. 

In the laboratory, an approximately equal volume of pentane 

(chromatographic grade) was added to each vial. The contents were stirred 

until the resin had been dissolved from the glass rod. The glass rod was 

removed, and the vial was tightly capped. The time between lifting the sample 

from the cut surface and the capping vial was usually less than 1 hour. Vials 

containing the prepared sample were held at 0°C until ready for analysis 2 to 8 

months later. 

Two variants of the severing procedure were used to study resin 

composition between annual rings and between internodes. For annual ring 

studies, the glass rod was carefully moved along a specific annual ring, and the 

sample for each ring of the tree was kept separate. For internodal studies the 

topmost internode was severed, and the resin sample taken as noted above. 

Then the next internode was severed, and so on down the tree. In one instance 

trees were sampled vertically by cutting a live limb off each whorl. This cutting 

of live branches was used most effectively on the edge trees of a nursery bed or 

on young plantation trees. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 201 
Chapter 5 Populati

on Studies of the Monoterpene Composition Smith 

of 4-to 12-Year-Old Half Siblings of P. ponderosa 

Trees that were to remain in the nursery bed or plantation were sampled by 

the basal micro-tap procedure described in Chapter 2. 

It needs to be stressed that during the analysis of the first set of half-siblings 

from Ranger Peak in 1976, it became clear that the composition of these 4- to 6-

year-old seedlings could be unstable or in a state of flux and might not be that 

of the tree when it matures. Therefore subsequent studies were designed to 

ascertain the magnitude of this condition and to determine when the 

monoterpene composition of young trees could be used for various types of 

analyses. GLC analysis was as described in Chapter 2 of this report. 

To repeat, all measurements reported in this chapter were of different 

trees of the same seed source; i.e., there were no successive measurements of the 

same trees. Chapter 8 does have data on successive measurements of the same 

tree in the study that resampled young trees. 

Tehachapi Transition Zone: Ranger Peak 

Seeds were collected in 1970 from four trees located between Figueroa 

Mountain and Ranger Peak on the Los Padres National Forest (fig. 5-1). This 

was the location of an 80-tree stand classed as the Tehachapi Transition Zone 

for P. ponderosa (see Chapter 3, P. ponderosa, stand #30). An additional 40-tree 

stand was sampled in the same general area about a mile away. No high­

limonene trees were found in the 80-tree stand, but one was found in the 

additional 40-tree stand. Trees were selected for cone collection on the basis of 

xylem monoterpene composition. The composition of the four female trees was 

listed (table 5-1). Tree RP-B37 was high in limonene and essentially without ßpinene and 3-carene; Trees RP-B41 and RP-B42 had moderate amounts of ß-pinene, 3-carene, and limonene; and Tree RP-2374 was high ß-pinene and 

without 3-carene but with moderate limonene. All four trees had moderate 

amounts of α-pinene and myrcene. Though these four trees were selected on 

the basis of monoterpene composition, they were fairly representative of the 

stand except for the high-limonene tree. 

Seeds were planted in the 1971 nursery. The bed was thinned in 1976 and 

again in 1978; the remaining few trees were cut in 1981. Thus all analyses were 

of different trees and not successive measurements of the same tree. Number of 

trees sampled proved to be a bit small. 

It was evident (table 5-1, figs. 5-2 and fig. 5-3) that ß-pinene and 3-carene 

were much higher than expected in the progeny and myrcene and limonene 

much lower than expected, when the composition of the parents and of the 

stand average, and the source of pollen, were considered. It was also readily 

apparent (figs. 5-2 and 5-3) that the frequency distributions of the major 

components were multimodal. Though there was some fluctuation in 

composition between sampling periods, this pattern of higher ß-pinene and 3-

carene, and of lower myrcene and limonene, held throughout the sampling 

period. However, the individual components were comparatively higher or lower with respect to the female parent (table 5-1). That is, for example, the progeny of RP-B37 were much lower than expected in limonene; yet compared 

to the progeny of the other three trees, RP-B37 was still highest in limonene, 

and almost by direct ratio. This general tendency held for other major 

components. The term' juvenile factor" was applied to this condition in young 

P. ponderosa. The presence and effect of the juvenile factor in this set of halfsibling progeny at Ranger Peak influenced much of the sampling in the 

subsequent research on young P. ponderosa. There may be some evidence that 

limonene and myrcene will increase with age and ß-pinene and 3-carene will 

decrease (table 5-2); larger samples could have improved the interpretation, 

particularly for the older trees. 

202 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
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-------------------------------------------------------- 

Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Table 5-1—Xylem monoterpene composition of the four parent P. (P), ponderosa at Ranger Peak the average composition of their 

wind-pollinated progeny (F) aggregated for 5 to 10 years of nursery growth, and the average composition of the surrounding 80-tree 

stand, the four parent trees, and the 195 aggregated progeny. N = number of trees; x=averages. 

Monoterpene1 

Tree Class of N α-p cam ß-p car my lim ß-ph ter 

tree 

percent-2------------------------------------------------

RP-B37 P 1 11.9 ** 2.6 0 15.7 69.7 ** 0 

F 39 14.2 ** 46.5 18.7 2.5 16.8 0.5 0.6 

RP-B41 P 1 6.2 0.1 27.2 21.1 16.8 21.8 0.6 0.4 

F 51 11.1 46.7 26.8 1.7 9.7 0.4 1.1 

0.2 

RP-B42 P 1 6.5 ** 39.2 23.2 9.9 22.9 1.3 2.0 

F 40 11.6 0.3 55.2 17.9 1.7 11.7 0.7 0.6 

RP-2374 P 1 12.0 ** 56.7 0 13.3 16.5 1.2 0 

F 65 14.5 0.4 55.0 18.3 1.8 8.3 0.4 0 

X P 4 9.2 0.1 30.2 11.1 13.9 32.7 0.8 ** 

X F 195 13.0 0.3 51.8 20.5 1.9 11.0 0.5 0.7 

X Stand 80 8.2 ** 36.7 25.2 13.1 17.3 ** 1.5 

1

α-pinene, camphene, ß-pinene, 3-carene, myrcene, limonene, ß-phellandrene, terpinolene. 2

Normalized, ** = trace. 

Table 5-2—Average composition of all half-siblings from the aggregate of the four trees at Ranger Peak (see table 5-1) for three periods of 

nursery growth. N = number of trees. 

Monoterpene1 

Age N α-p cam ß-p car myr lim ß-ph ter 

years 

---------------------------------------------------percent

2 

5 126 14.7 0.1 51.7 23.8 1.2 6.7 0.5 0.8 

7 58 9.4 0.6 51.2 14.6 3.1 19.9 0.4 0.7 

10 11 11.3 ** 54.9 14.3 3.3 14.7 1.0 0.4 

1

α-pinene, camphene, ß-pinene, 3-carene, myrcene, limonene, ß-phellandrene, terpinolene. 2

Normalized, ** = trace. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 203 
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-2—Frequency distribution of the 

amount of noted monoterpenes in the 5- to 

10-year-old progeny of P. ponderosa RP-B37 

and RP-B42; each dot is measurement of one 

tree; [▲] is average of set. 

(continues on next page). 

204 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 205
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-3—Comparative frequency 

distribution of the amount of the noted 

monoterpenes of the mature 80-tree 

stand of P. ponderosa at Ranger Peak and 

of the aggregate 5- to 10-year-old progeny of four female parent trees: RP-B37, 

RP-B41, RP-842, RP-2374; each dot is 

measurement of one tree, except where 

. indicates each is n trees; [▲] is average of set. 

(continues on the next page) 

206 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 207
Chapter 5 Populati

on Studies of the Monoterpene Composition Smith 

of 4-to 12-Year-Old Half Siblings of P. ponderosa 

This might be an appropriate place to discuss myrcene because it was 

classed as a major monoterpene, yet at most times it seems to be more like a 

minor one. Myrcene was always present in P. ponderosa throughout its 

entire range. It was nearly always present in small amounts, ranging from 

about 2 to 20 percent but mostly 5 to 15 percent, but in a rare tree it can be 

greater than 25 percent. Because both myrcene and limonene seemed to 

increase very slowly with age, one might speculate that myrcene was linked 

to limonene positively, in much the same way that terpinolene is linked to 

3-carene and sabinene. But myrcene was found in trees that essentially lack 

limonene, whereas terpinolene was never present when 3-carene and 

sabinene were absent. Thus myrcene may be linked to limonene, may be 

produced in small amounts by isomerization or biosynthetic by-products, 

and, as will be shown later in the discussion of full siblings, was found as a 

rare allele. No tree with an unusually large amount of myrcene was found in 

the Ranger Peak progeny, despite having a high stand average, and it 

appeared that alleles for myrcene were lacking, though a rare (0-1) set 

would be expected at least. Thus, the large amount of myrcene in the 

Southern California mountains appeared to be caused by its positive linkage 

to limonene or to isomerization. One parent tree at Adin Summit, that was 

used in controlled breeding, had about 30 percent myrcene and was assigned 

a (0-1) set of alleles; the frequency distribution of the progeny of this tree 

very easily supported the assignment of an (0-1) set of alleles for myrcene to 

that tree; the progeny of this tree will be discussed in Chapter 6 of this 

volume. In the range-wide study of P. ponderosa, reported in Chapter 3 of 

this volume, one tree was found with about 50 percent myrcene. One might 

speculate that this tree had a (1-1) set of alleles for myrcene and was the 

product of the combination of two rare (0-1) alleles. The positive linkage of 

limonene and myrcene is a fascinating biological condition in that limonene 

was the more toxic of the monoterpenes to western pine beetle, and therefore 

enhanced tree survival, whereas myrcene synergized the attractive 

pheromone of the beetle and therefore enhanced beetle survival. This 

phenomenon was difficult to reconcile with the theory of coevolution; i.e., 

two chemicals were linked in some genetic way, yet one seemed to favor 

tree survival and the other seemed to hasten its death. 

The primary objective of the study was to obtain a large selection of trees 

with a diverse array of monoterpene compositions for host resistance and resin 

studies. Ten such types of composition were found among the progeny of the 

four parent trees (fig. 5-4). One type of particular note was #1 which was 

classed as an ultra-high limonene, between 70 percent and 90 percent; this type 

was found, but not commonly, in the progeny of RP-B37, the high-limonene 

parent tree. An ultra-high limonene tree had not been found in natural 

populations of P. ponderosa. 

Progeny classed as high limonene were produced by trees RP-B42 and RP2374, two trees not classed as high limonene. Because the progeny that were 

classed as high limonene had no ß-pinene also, one might assume a (0-1) set of 

alleles for ß-pinene in the two parents. 

The results of the study at Ranger Peak were not strongly encouraging and 

may have been weakened by inadequate sampling in the older sets of trees. 

Though confident analysis and conclusions could not be made, the results were 

quite valuable in determining the design and conduct of subsequent studies of 

half- and full siblings. 

An early attempt to bioassay resistance was made, using these small trees, 

and the results were inconclusive (see Chapter 9). However, the experience did provide better guidance in the conduct of the other breeding and culturing 

studies. Tree RP-B37 was not used in controlled breeding, but it would have 

been interesting and helpful to do so because it had much lower α-pinene than 

208 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

any of the other high limonene trees that were used, as reported in the section 

on full siblings. By its composition one would postulate that RP-B37 had no 

alleles for ß-pinene or 3-carene, and might not have alleles for α-pinene 

and myrcene. 

Sierra Pacific Region: Adin-Placerville 

Three trees are discussed in this section: AS-3139, AS-3187, IFG-P15 (table 5-3); 

trees AS-3139 and AS-3187 were at Adin Summit, IFG-P15 on the Eldorado 

National Forest (NF) (fig. 5-1). Tree AS-3139 was also a graft growing at the 

Institute of Forest Genetics; seeds were collected from it at Adin and from the 

graft at IFG. AS-3139 was a high limonene tree and was used in the breeding 

programs. IFG-P15 was growing on the Eldorado NF near IFG; it was included 

for comparison of progeny. AS-3187 was also growing at Adin Summit and was 

used in controlled breeding programs. Progeny of AS-3139 were grown in the 

nursery and in the plantation; the progeny of IFG-P15 and AS-3187 were grown 

only in the nursery. 

Again, as with the progeny from Ranger Peak, the composition was not 

what was expected (table 5-3) considering the composition of the female parent 

and the composition of the surrounding stand, the source of pollen. This is 

attributed to the juvenile factor. But the compositions of the progeny were still 

relatively comparable, as noted for the Ranger Park progeny; i.e., the progeny 

of AS-3139 were highest in myrcene and limonene, and those of AS-3187 were 

highest in ß-pinene and 3-carene. 

There were some shifts in the composition of nursery-grown progeny of 

AS-3139 and IFG-P15 over the early years of nursery growth (table 5-4), but no 

strong trends were evident, as was somewhat evident in the Ranger Peak 

progeny. There were, however, small but consistent increases in myrcene. 

Could this suggest that myrcene was isomerized from limonene or related to it 

in some way? The largest shifts in myrcene were in the progeny of AS-3139, the 

high-limonene tree. The aggregate frequency distributions strongly suggest 

multimodal distributions for α-pinene, ß-pinene, 3-carene, myrcene, and 

limonene (fig. 5-5). There were large differences between the nursery-grown 

seedlings and the plantation-grown seedlings of AS-3139 (fig. 5-5). The largest 

difference was in α-pinene; the nursery-grown stock averaged 13.9 percent, and 

the plantation-grown stock averaged 25.5 percent. Limonene was the converse 

with 27.3 percent in the nursery and 15.3 percent in the plantation (table 5-4). Beta 

-pinene was much higher in the plantation, and 3-carene much lower. 

The frequency distribution of the individual monoterpenes clearly showed 

the great differences between the nursery-grown and plantation-grown plants 

(fig. 5-5). The over application of a phytocide during the second and third 

growing seasons in the plantation was considered to have caused very severe 

stress to all trees in the plantation. This was the first evidence to suggest that 

stress could affect quantitative composition. Many trees were killed and those 

that lived had greatly reduced terminal growth for 2 years or more. However, 

by the time the trees were sampled in 1988 at 10 years, most trees were growing 

normally as indicated by the 18 in and 24 in. in terminal growth. Thus, there 

was a residual effect of stress. 

There was no appreciable difference between the progeny of AS-3139 from 

the Adin tree or from the Placerville graft. This might be expected because both 

localities are in the Sierra Pacific Region of P. ponderosa and, therefore, have 

about the same general pollen background for xylem monoterpenes. 

It is of particular note that for the progeny of AS-3139 the 27 percent 

average for limonene was considerably higher than the 14 percent for the 

progeny of WP-3298 and WP-3352, the two high-limonene trees at Wheeler 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 209 
--- --- 

------------- ------------ ------------- ------------ ------------- 

--- 

-------------- ----- 

Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-4—Ten types of 

monoterpene composition in the 5- to 

10-year-old progeny of the four noted 

female P. ponderosa parents at Ranger 

Peak, the occurrence of the 10 types in 

the four sets of progeny: ([●]) = occurs 

commonly, ([○]) = occurs not commonly. 

NOTE: footnotes for all of the tables and 

figures on the bottom of the page. 

Type Monoterpene1 Parent Tree 

number 

α-p ß-p Car my lim RP-B-37 RP-B-41 RP-B-42 RP-2374 

Pct

2 

1 16 10 2 3 69 ○

2 4 0 39 4 50 ○ ○ ○

3 45 9 2 3 40 ○

4 8 1 54 9 27 ○

5 10 58 0 4 25 ○ ○

6 9 20 49 5 15 ○ ● ●

7 14 73 0 1 11 ● ●

8 10 39 41 1 9 ● ●

9 13 57 24 1 4 ● ● ● ●

10 15 75 0 6 2 ● ● ● α-pinene, ß-pinene, 3-carene, myrcene, limonene 

Table 5-3—Xylem monoterpene composition of the three parent trees P. ponderosa (P) at Adin-Placerville, the average composition of their windpollinated progeny (F) aggregated for 4 to 12 years of nursery growth, and the average composition of an 80-tree stand at Adin and at Placerville 

Monoterpene1 

Tree 

number Class Trees Age α -p cam ß -p car my lim ß -ph ter 

number years ----percent

2 

AS-3139 P 1 40+ 17.8 0 0.7 0 22.1 52.9 0.7 0 

F 69 4-12 13.9 0.2 21.9 28.1 7.0 27.3 0.1 1.6 

AS-3187 P 1 40+ 9.2 0.1 22.7 22.7 14.3 28.5 0.9 1.0 

F 10 4-12 8.7 0.1 25.8 45.4 5.3 12.0 0 2.7 

IFG-P-15 P --- --- no data --- --- ---

F 66 4-12 7.3 0.1 36.4 36.5 4.1 13.1 0.3 2.0 

Adin stand 80 40+ 6.0 0 20.5 44.5 14.5 12.5 0.5 2.0 

Placerville stand 80 40+ 6.0 0 29.5 34.5 13.0 15.5 ** 2.0 

1 α -pinene, camphene, ß -pinene, 3-carene, myrcene, limonene, ß -phellandrene, terpinolene. 2

 Normalized, ** = trace. 

210 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-5—Frequency distribution of the amount of the 

noted monoterpenes of the 

progeny of the P. ponderosa listed on the right, with two different sources of pollen (Adin, 

IFG) and two places of growth 

(nursery, plantation); each dot 

is measurement of one tree; 

[▲] is average of set. 

(continues on the next page). 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 211 
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Table 5-4—Average monoterpene composition of the wind-pollinated progeny of AS-3139 and lFG-P15 for 4-12 years of growth in the 

nursery. N = number of trees, x=average. 

Trees Years N Monoterpenes1 

growth α-p cam ß-p car myr lim ß-ph ter 

percent -2 

AS-3139 5 6 12.9 ** 28.0 17.5 3.2 37.4 0.6 0.3 

9 17 16.8 0.7 18.7 32.0 6.1 24.3 0.1 1.7 

10 18 13.9 0.1 21.6 24.7 7.8 30.4 ** 1.4 

10 13 14.2 0.1 28.0 25.9 5.5 24.8 ** 1.4 

11 15 10.6 ** 19.0 33.8 9.5 25.0 ** 2.1 

X (Σ69) 13.9 0.2 21.9 28.1 7.0 27.3 0.1 1.6 

IFG-PI5 5 14 7.3 0.5 38.8 34.3 3.2 13.4 0.5 2.1 

9 13 8.4 ** 38.4 35.6 3.5 11.4 0.5 2.0 

10 7 7.0 0.2 37.9 30.6 3.8 19.2 ** 1.4 

10 21 7.3 0.1 36.2 37.7 4.4 12.2 0.2 2.6 

11 II 6.3 0.1 30.6 41.8 5.3 13.1 0.2 2.6 

X (Σ66) 7.3 0.1 36.4 36.5 4.1 13.1 0.3 2.0 

1 α-pinene, camphene, ß-pinene, 3-carene, myrcene, limonene, ß-phellandrene, terpinolene. 2-Normalized, ** = trace. 

212 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smi

th Population Studies of the Monoterpene Composition Chapter 5 

of 4-to 12-Year-Old Half Siblings of P. ponderosa 

Peak that will be discussed in the next section on the Escalante North Transition 

Zone. The limonene background in pollen, 12 percent for Adin and 14 percent 

for Wheeler, would lead one to expect a greater amount of limonene in the 

progeny from Wheeler than from Adin. I would postulate that this could again 

be an expression of stress in the Wheeler progeny growing at IFG far out of 

their Wheeler Peak provenance, and even out of their resin ecotype region, 

whereas the progeny of AS-3139 were growing in their resin ecotype region, 

though about 250 miles away. In fact all three trees located in the Sierra Pacific 

had progeny with greater limonene than the progeny of comparable trees at 

Wheeler Peak. Likewise, the progeny of AS-3139 were much higher in limonene 

than the progeny of RP-B37, the high limonene tree at Ranger Peak, 27 percent 

vs. 17 percent. 

There were only 10 nursery-grown progeny of AS-3187. As expected, the 

average composition for nearly all monoterpenes was quite different from that 

of the progeny of AS-3139 (table 5-3), and the frequency distributions were also 

quite different (fig. 5-5). There were insufficient trees to determine if there were 

changes over time. It was obvious that the differences noted above were a 

reflection of the differences between the two parents, because one can assume 

that the background pollen was about the same for both trees. 

The results with the progeny from Adin and IFG parent trees were far more 

encouraging than results with the Ranger Peak trees. There was a marked 

improvement in sampling numbers, and composition did not change with age 

enough to preclude confident analysis and conclusions. The average 

composition and the frequency distribution of individual monoterpenes of the 

progeny of AS-3139 differed markedly from that of AS-3187 and IFG-P15, 

which shows the difference in the female parents. 

Twelve types of composition were found among the progeny of the three 

parent trees (fig. 5-6). These types clearly showed the difference between the 

female parents. The two types of ultra-high limonene (between 70 percent and 

90 percent), #1 and #2 (fig. 5-6), were found only in the progeny of AS-3139. 

Such ultra-high compositions have not been found in natural stands. The 

limonene in the progeny of AS-3187 and IFG-P15 was well below 30 percent. 

Comparisons of the progeny of AS-3139 and those of the other two high 

limonene trees at Wheeler Peak, WP-3298 and WP-3352, will be made at the end 

of the section on Wheeler Peak. 

Escalante North Transition Zone: Wheeler Peak 

Seeds were collected from 13 trees at Wheeler Peak in 1971 (fig. 5-7, table 5-5)

and planted in several nurseries starting in 1972. Wheeler Peak was in the 

Escalante North Transition Zone of P. ponderosa (see Chapter 3). Some seedlings 

of the two high-limonene parents, trees WP-3298 and WP3352, were also 

transplanted to the 1978 plantation. Resin samples from all trees were obtained by plant severing or by micro-tap in the nursery, and by micro-tap in the plantation (see Chapter 2 and introduction to Chapter 6 for a description of this procedure). 

Where possible, sets of the same nursery-grown half-siblings were 

compared for each period of growth and then aggregated into three or four age 

classes to get greater numbers per class. The aggregated classes gave a much 

better definition of the frequency distribution and averages. 

In all cases, all trees in all sets are different, though taken from the same 

basic lot of seed; i.e., there were no successive measurements of the same trees. 

We were encouraged that, in general, the results with these 13 sets of progeny 

did not show as strong a juvenile effect as was found in the Ranger Peak 

progeny, though there was still some effect. I am inclined to believe that the 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 213 
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-6—Twelve types of 

monoterpene composition in the progeny of the three noted parent P. ponderosa, aggregated for 4 to 12 years of 

nursery growth, and the occurrence of 

the types in each set of progeny: ([●]) 

= occurs commonly, ([○]) = occurs 

not commonly. 

Type Monoterpene 1 Parent Tree 

# α-p ß-P car my lim AS-3139 AS-3187 IFG-P15 

Pct 2 

1 7 0 0 2 90 ○

2 16 10 2 3 69 ○

3 4 0 39 4 50 ●

4 32 6 1 15 47 ○

5 14 39 0 5 42 ○

6 8 1 54 9 27 ●

7 10 58 0 4 25 ○ ○

8 7 34 34 4 20 ● ● ○

9 1 ii 51 2 20 ●

10 9 20 49 5 15 ○ ○

11 10 39 41 1 9 ○ ●

12 54 33 0 1 3 ○ 1

:α-pinene, ß -pinene,3-carene, myrcene, limonene 

2

: Normalized 

Table 5-5—Monoterpene composition of 13 parent trees at Wheeler Peak and of the average composition of the surrounding 

80-tree stand (WP) 

Monoterpene1 

Tree Number α-p cam ß-p car my lim ß-ph ter 

percent2 

WP-3292 12.8 0.1 75.7 0.1 8.5 1.3 1.7 0.1 

WP-3293 7.1 0.1 10.8 67.0 9.6 0.8 0.4 4.0 

WP-3294 4.6 0 5.0 55.8 5.0 26.1 0.7 2.8 

WP-3298 25.6 0.1 0.4 0 16.1 57.9 0 0 

WP-3299 6.4 0 0.2 43.0 7.9 40.4 0.8 1.1 

WP-3301 6.5 0 0.6 68.8 18.2 0.6 0.6 4.6 

WP-3312 4.8 0 7.3 33.8 3.5 48.0 1.0 1.7 

WP-3318 3.6 0.1 10.4 18.4 3.0 40.6 0.8 0.7 

WP-3320 12.0 0 0.3 60.7 5.6 26.6 0.4 2.7 

WP-3359 24.3 0.1 31.3 42.5 10.6 0.6 1.0 2.6 

WP-3352 22.4 0.2 0.4 0.1 13.1 56.9 0 0 

WP-B475 7.0 0.2 62.7 0 12.5 1.4 0.8 0 

WP-B477 6.0 0.1 16.4 63.2 9.4 0 0.6 3.5 

X WP 6.9 0.1 29.0 34.0 13.0 15.0 1.0 2.0 

1

α-pinene, camphene, ß-pinene, 3-carene, myrcene, limonene, ß-phellandrene, terpinolene. 2

Normalized. 

214 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-7—Location of the Wheeler 

Peak stand of P. ponderosa in eastern 

Nevada; see figure 5-1 for general location. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 215
Chapter 5 Populati

on Studies of the Monoterpene Composition Smith 

of 4-to 12-Year-Old Half Siblings of P. ponderosa 

juvenile effect may be strongest in the types of composition found in the 

Tehachapi Transition Zone at Ranger Peak. 

The following discussion will compare the compositions and frequency 

distributions of individual components of pairs of parents with similar and 

with dissimilar monoterpene compositions, will compare the progeny of groups 

of parents, and will compare the types of composition found among the progeny 

of all trees in the study. The average composition of the aggregate nursery-

grown progeny of each of the 13 parents was listed (table 5-6). In some of the 

sets of comparison in the rest of this section on Wheeler Peak, the base line scale 

may not be the same for both trees for a given component. In most cases, the 

scales will be the same. 

Comparison of Progeny of Parents with Similar Composition 

Trees WP-3298 and WP-3352 

Both trees were classed as high limonene, nearly 60 percent, and essentially 

without ß-pinene and 3-carene (table 5-5); neither tree served as a female in 

controlled breeding, but both served as males. Ten sets of nursery-grown 

progeny ranging in age from 4 to 12 years and one set of 9-year-old plantation 

trees were examined. The average composition varied somewhat for each 

nursery period as illustrated by the progeny of WP-3352, but there was no 

clearly defined trend (table 5-7); small sample size may have caused some of the 

apparent variation. This general pattern prevailed for the progeny in all sets. 

When the data were aggregated into three age classes for each set of progeny, 

variation with time became very small and there was no discernible trend in 

either set of progeny (fig. 5-8). There was no sharp tendency for α-pinene or ßpinene to decrease. The multimodal configuration of the frequency distributions 

of the two major monoterpenes was clearly evident. 

The set of plantation plants was lower in limonene and 3-carene and higher in 

α-pinene and ß-pinene, and this may have been caused by the phytocide-related 

stress (fig. 5-8). The data from plantation trees were not used in further analyses. 

The effect of the phytocide-related stress was not as great as in the Adin/IFG progeny; and I attribute this to the presence of additional stress in all the Wheeler progeny caused by growing out of the seed provenance. Therefore, the added 

stress of the phytocide might not have been as great. Some of the fluctuation in the 

results could have been attributed to the large range in sample number. 

When all nurseries were aggregated into one set, omitting plantation trees, 

so that larger numbers of measurements were in each frequency distribution, 

the similar characteristics of the distributions of the progeny of the two parent 

trees were much clearer (fig. 5-9). Five of the monoterpenes had a multimodal 

distribution and a large range as follows (fig. 5-9): α-pinene, 1 to 85 percent; ß-

pinene and 3-carene, 0 to 75 percent; myrcene, 1 to 35 percent; limonene, 0 to 60 

percent. The large number of values in the low mode of limonene, 0 to 6 

percent, was puzzling. Because the female parents were high in limonene and 

assigned a (1-1) set of alleles, at least a moderate amount of limonene would 

have been expected in all progeny. It will be shown in the next section on full 

siblings (Chapter 6) that the progeny of high limonene x high limonene never 

had low limonene as expected; however, ß-pinene and 3-carene were essentially 

lacking in such trees. Therefore, it was possible that limonene was not yet fully 

expressed in young progeny because of the excessive juvenile activity of the 

other monoterpenes, particularly ß-pinene and 3-carene. There was a tendency 

for the frequency of low limonene trees to decrease with age (fig. 5-8) to give 

added support to the possibility that limonene was not fully expressed in 

young trees, but does so with age. Because α-pinene was much higher than 

expected in young trees, it was possible that α-pinene outcompetes limonene 

for the C-5 precursor in young trees. 

216 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-8—Frequency distribution of the 

amount of the noted monoterpenes of the 

wind-pollinated progeny of two P. ponderosa 

with similar composition, WP-3298 and WP3352, with three ages of nursery growth 

(nur) and one of plantation growth (plan), as 

of 

listed on the right; each dot is measurement 

one tree; except where indicates each 

represents n trees; [▲] is average of set. 

(fig 5-8 continues on next 6 pages). 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 217 
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

218 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 219
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

220 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 221
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

222 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 223
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-9—Frequency distribution of the 

amount of the noted monoterpenes in the 

progeny of two P. ponderosa with similar 

composition, WP-3298 and WP-3352, aggregated for 4 to 12 years of nursery growth; 

each dot is measurement of one tree except 

w

average of set. 

here indicates each is n trees; [▲] is 

224 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 225
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Table 5-6—Average composition of the wind-pollinated progeny of the 13 listed P. ponderosa at Wheeler Peak aggregated for 4 to 12 

years of nursery growth; see table 5-7 for composition of female parent; * indicates a relatively high amount of the component in the 

.female parent. 

Tree number Trees Monoterpene1 

α-p cam ß-p car m lim ß-ph ter 

number percent2 

WP-3298 177 31* * 18 27 5 14* ** 1 

WP-3352 193 20* 1 23 31 6 15* 1 1 

WP-3299 145 14 * 23 38* 4 19* 1 2 

WP-3312 145 19 * 22 38* 5 14* 1 2 

WP-B475 72 26* * 45* 13 10 3 1 1 

WP-3301 78 19 1 23 44* 8 4 1 2 

WP-3320 94 7 * 23 49* 4 12* 1 2 

WP-3359 98 13 * 40* 33* 5 4 1 2 

WP-3292 27 13 * 50* 26 4 2 1 1 

WP-3293 24 9 * 32 48* 5 3 1 2 

WP-3294 90 14 * 28 36* 4 12* * 2 

WP-3318 32 22* * 30 30* 2 14* * 1 

WP-B477 25 11 * 33 46* 5 2 1 2 

1

α-pinene, camphene, ß-pinene, 3-carene, myrcene, limonene, ß-phellandrene, terpinolene. 2

Normalized. 

Table 5-7—Average xylem monoterpene composition of 10 sets of progeny of tree WP-3298 at Wheeler Peak with varying age of nursery growth at 

IFG when sampled, and one set of 9-year-old plantation-grown trees; and composition of the total sample and of the female parent (P). N = number 

of trees; x=average or sum( ). 

Source1

 and Monoterpenes2 

age 

N α-p cam ß-p car myr lint ß-ph ter 

percent3 

Nur- 4 41 35.1 0.3 19.1 26.2 6.2 11.5 0.5 1.1 

Nur- 5 11 31.1 * 24.1 33.9 3.2 5.3 0.5 1.6 

Nur- 5 6 32.2 0.6 28.0 22.5 5.7 9.4 0.6 0.8 

Nur- 6 26 27.8 3.1 22.1 27.3 5.1 12.5 0.8 1.0 

Nur- 6 35 31.5 * 16.4 25.1 4.8 20.6 0.2 0.8 

Nur- 9 8 40.3 0.1 19.3 16.3 4.5 17.5 0.5 0.9 

Nur- 9 7 26.2 * 11.8 34.0 4.7 21.9 0.6 1.9 

Nur- 10 15 32.3 0.1 9.4 41.8 5.0 8.9 0.1 2.4 

Nur- 11 24 26.4 0.1 18.9 29.6 5.8 17.1 0.5' 1.6 

Nur- 12 4 18.6 * 37.8 15.7 5.7 20.1 0.4 1.6 

Plan- 9 11 42.6 0.1 18.0 18.6 5.9 13.2 0.2 1.2 

X 

P4 

(188) 

1 

31.8 

25.6 

0.2 

0.1 

18.9 

0.1 

27.4 

0 

5.3 

16.1 

14.3 

57.9 

0.4 

0 

1.3 

0.1 

1

Nur = nursery; Plan = plantation. 2

α-pinene, camphene, ß-pinene, 3-carene, myrcene, limonene, ß-phellandrene, terpinolene. 3

Normalized; * = trace. 4

Composition of female parent, WP-3298.

226 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smi

th Population Studies of the Monoterpene Composition Chapter 5 

of 4-to 12-Year-Old Half Siblings of P. ponderosa 

Camphene was unusually high in the 6-year set of trees with an average of

about 3 percent and with a few individual measurements between 4 and 6 

percent. The trend to this unusually high level of camphene may have begun in 

the 4th- and 5thyear sets (fig. 5-8, table 5-7). Then, after the 6th year, camphene 

returned to the usual trace amount: 0.1 to 0.2 percent. This phenomenon, called

the camphene anomaly, was apparent in all Wheeler Peak progeny. There was 

a lesser but noticeable trend toward higher camphene in the 7-year set of 

Ranger Peak progeny and the 5th and 9th year sets of Adin/IFG progeny. But this phenomenon was not apparent in any of the sets of full siblings, which will

be discussed in Chapter 6. I postulate three explanations for this unusual phenomenon: (1) It could be a very transient and juvenile anomaly of P. ponderosa seedlings which may or may not be expressed. (2) It could be some 

other transient chemical that chromatographs as camphene. Though it checked 

out as camphene by internal standards, one cannot exclude some other 

chemical with the chromatographic properties of camphene. (3) It could be 

either of the two above but is expressed irregularly in different nursery beds 

or to other culturing practices. This apparent but small anomaly did not 

appreciably affect the measurements of the five major monoterpenes nor any 

of the analyses or conclusions. 

Though there was general similarity between the progeny of WP-3352 and 

WP-3298 (fig. 5-9), as one might expect, some differences suggest that the two 

parent trees are not completely alike in monoterpene genetics or characteristics, 

or they respond slightly differently to environmental conditions. This difference 

was most clearly shown in α–pinene, which is much higher in the progeny of 

WP-3298 than in those of WP-3352, and ß–pinene which was much lower in the 

progeny of WP-3298 than in WP-3352; but this difference could simply be the 

natural variation in the distribution .of pollen. It is my assessment that the 

difference between the progeny of the two trees in the plantation was caused by

differential overdosing of a phytocide. It was not possible to attribute the effect

of a phytocide to individual trees. Some minor genetic structure might also 

cause such differences between the two sets of progeny, but such a minor 

structure has not been clearly shown or explained.

One might also speculate that the progeny of both WP-3298 and WP-3352 

were growing far outside their seed and "resin" zones, and were under some 

degree of stress. Reaction to this stress was a modification of monoterpene 

composition and to the general stability of the system, and fluctuations will 

probably be more pronounced and variable in an unstable system. 

Types of composition will be discussed in a section at the end of this section 

on Wheeler Peak. 

From these results the structure of alleles for both trees was tentatively 

placed at (0-1), (0-0), (0-0), (0-0),.and (1-1), respectively, for α–pinene, ß–pinene, 

3-carene, myrcene, and limonene. The assignment of alleles will be developed

further in Chapter 6 

Trees WP-3299 and WP-3312 

Each tree was near-high limonene, 40 to 45 percent, without ß–pinene, but with 

high 3-carene, 34 to 43 percent (table 5-5). Six sets of nursery-grown trees were 

examined with ages varying from 4 to 12 years; there were no plantation sets. 

The average composition of the progeny varied slightly from set to set; but 

when the data were aggregated into three age classes with larger numbers, 

variation was greatly reduced (fig. 5-10), though ß–pinene and limonene varied 

much more than in the progeny of the previous two trees, WP-3298 and WP3352. The amount of α–pinene was considerably lower than in the progeny of the two previous trees, reflecting a much lower α–pinene in the female parents, 

and suggesting a (0-0) set of alleles for α–pinene in both trees: WP-3299 and 

WP-3312. The level of limonene was nearly the same in the progeny of all four 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 227 
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-10—Frequency distribution of 

the amount of the noted monoterpenes of the progeny of two P. ponderosa 

with similar composition, WP-3299 and 

WP-3312, at three ages of nursery 

growth, listed on the right; each dot is 

measurement of one tree; [▲] is aver-age 

of set. 

228 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 229 
Chapter 5 Populati

on Studies of the Monoterpene Composition Smith 

of 4-to 12-Year-Old Half Siblings of P. ponderosa 

trees, WP-3298, WP-3352, WP-3299, and WP-3312, despite a much lower 

limonene level in the WP-3299 and WP-3312 parents. It would appear that the 

genetic level of limonene was the same in all four parent trees, but the 

competitive presence of at least one allele for 3-carene in WP-3299 and WP-3312 

resulted in a lesser amount of limonene in the WP-3299 and WP-3312 parents. 

The absence of a mode near zero for 3-carene in the progeny of WP-3299 

suggested a (1-1) set of alleles in the parent tree; that is, all progeny of WP-3299 

would have at least one allele for 3-carene and therefore no mode near zero. 

The progeny of WP-3312 had a mode for 3-carene near zero, though it was quite 

small, and the ratio of the size of the modes did not rule out a (0-1) set of alleles 

in WP-3312. Again, each age set is a different set of trees from the same seed lot. 

Again, as with the progeny of trees WP-3298 and WP-3352, there was 

considerable range in the frequency distribution of components, but the same 

generalized pattern seemed to prevail when the samples were aggregated into 

three time sets (fig. 5-10), and still further into one set of all ages (fig. 5-11). 

There were some small differences; the progeny of WP-3299 had a smaller 

mode near 0 percent for limonene and 3-carene. The camphene anomaly was 

also present in the 6-year set of progeny; this was discussed under WP-3298 and WP-3352. The multimodal character of the distributions of the five major 

components was clearly evident. The large mode for limonene near zero 

could suggest a (0-1) set of alleles for limonene in the female parents. But 

the breeding studies reported in the next chapter clearly show that both 

trees have a (1-1) set. As noted before, the mode near zero was probably 

caused by the juvenile factor. 

Trees WP-3320 and WP-3294 

These two trees were somewhat similar to WP-3299 and WP-3312, except that 

WP-3294 and WP-3320 were lower in limonene, ca. 27 vs. 40 percent, and higher 

in 3-carene, ca. 58 vs. 36 percent (table 5-5). A total of 80-85 nursery-grown 

progeny of each tree was examined; the averages for the two sets were very 

similar. Quite different from the progeny of the previous two sets of progeny, 

the average amounts of α–pinene, ß–pinene and limonene in the progeny of 

WP-3320 varied much less over time (fig. 5-12). There was some slight shifting 

over time in the progeny of WP-3294 (table 5-8). 

The frequency distributions of both sets of progeny had about the same 

characteristics when all trees were aggregated into one class (fig. 5-13). There 

was one small puzzling difference between the two distributions. The progeny 

of WP-3320 had no mode near zero for 3-carene, a condition one would expect 

with an assignment of a (1-1) set of alleles for the 56 percent in the parent tree. 

On the other hand, three of the progeny of WP-3294 were at zero where one 

would expect none, because again one would be inclined to assign a (1-1) set of 

alleles for the 61 percent. If, however, a (0-1) set is assigned to WP-3320, a much 

more substantial mode than the one found would be expected at 0. The 0 

percent for three of the progeny of WP-3320 could be caused by: (1) rogues, (2) 

some procedural error, (3) or another effect of the juvenile factor. But the 

evidence still seemed to justify assigning the parents a (1-1) set of alleles for 3- carene. The camphene anomaly was present in the progeny of both parents. The frequency distribution of limonene suggested a (0-1) set of alleles in each parent. Neither tree was used in controlled breeding, which could have resolved 

the question. The frequency distributions for ß–pinene were nearly identical for 

the progeny of both trees with a large mode near zero and 2 to 3 other modes at 

about 18 percent and more than 45 percent. One would have to assign a (0-0) set 

of alleles for ß–pinene in both parent trees; and the zero mode supported this. 

The larger-than-expected values for the remainder of the distribution was 

attributed to the juvenile factor. Apart from these rather small differences, the 

frequency distributions were quite similar. 

230 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Table 5-8—Average xylem monoterpene composition of wind-pollinated progeny of tree WP-3294 for 4-12 years of nursery 

growth at IFG; and average composition of total sample and of the female parent (P). N = number of trees. 

Years in N Monoterpene1 

nursery 

α-p cam ß-p car my lim ß-ph ter 

percent2 

4 7 11.1 0.2 26.1 44.1 4.5 10.4 0.8 2.3 

6 29 12.3 0.1 29.4 37.6 2.9 14.8 0.5 1.9 

9 8 10.8 0.1 49.7 33.7 2.8 1.9 0.3 0.7 

11 27 17.3 0.2 19.1 41.8 5.7 12.8 0.6 2.3 

12 8 8.7 0.1 25.2 47.8 4.8 9.6 0.8 3.0 

X (Σ79) 13.4 0.1 27.4 40.2 4.2 11.9 0.6 2.1 

P3 1 4.6 0 5.0 55.8 5.0 26.1 0.7 2.8 

1

α-pinene, camphene, ß-pinene, 3-carene, myrcene, limonene, ß-phellandrene, terpinolene. 2

Normalized. 3

Composition of female parent, WP-3294.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 231 
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-11—Comparative frequency 

distribution of the amount of the noted 

monoterpenes in 4- to 12-year-old halfsibling progeny of two P. ponderosa, WP3299 and WP-3312, aggregated for 4 to 

12 years of nursery growth; each dot is 

measurement of one tree; where indicates each is n trees; [▲] is average of 

set. 

(continues on the next page) 

232 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 233
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-12—Frequency distribution of 

the amount of the noted monoterpenes 

of the progeny of P ponderosa WP-3320 

with four periods of nursery growth, listed on the right; each dot is measurement 

of one tree except where indicates 

each is n trees; [ ▲ ] is average of set. 

(continues on the next page). 

234 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 235
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-I3—Comparative frequency 

distribution of the amount of the noted 

monoterpenes of the aggregated 4- to 12-

year-old progeny of two P ponderosa with 

similar composition, WP-3320 and WP3394; each dot is measurement of one tree 

except where indicates each is n trees; 

[▲] is average of set. 

236 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 237
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Trees WP-3293 and WP-B477 

The parent trees had nearly identical compositions (table 5-5): very high 3-

carene at about 65 percent with small amounts of α–pinene, ß–pinene, and 

myrcene, and with very small amounts of limonene. The averages for the two 

sets were nearly identical. There were insufficient data for a clear assessment of 

time of growth of nursery-grown progeny, but the evidence with other sets of 

progeny suggested that they could be aggregated into one set (fig. 5-14). There 

were zero or near-zero modes for α–pinene, ß–pinene, myrcene, and limonene, 

and there was no zero mode for 3-carene with all the values above 20 percent 

which would be expected from a (1-1) set of alleles. All limonene in both sets of 

progeny was well below 15 percent, with about three quarters of the values 

near zero. Some values above 20 percent would have been expected for 

limonene when the pollen background was considered; that is, one would have 

expected an allele for limonene in some of the progeny. Again this could be an 

effect of the juvenile factor; i.e., in young trees the alleles for limonene did not 

function, functioned incompletely, or were outcompeted by ß–pinene or 3-

carene. The data suggested a (0-1) set of alleles for ß–pinene and limonene, and 

a (0-0) set for α–pinene and myrcene, in addition to the (1-1) set of alleles for 3-

carene in both parents. Neither parent was used in controlled breeding to check 

out these assignments. 

Comparison of Progeny of Parents With Dissimilar Composition 

Trees WP-3301 and WP-B475 

The two trees differed, respectively, as follows for WP-3301 and WP-B475: ß– 

pinene,1 percent vs. 65 percent; 3-carene, 69 percent vs. 0 percent; α–pinene, 7 

percent vs. 22 percent (table 5-5). Both parent trees were very low in limonene at 

about 1 percent. There was a bit more shifting overall in composition over time, 

but this may be a reflection of inadequate sampling for some periods (fig. 5-15). 

The difference between the two parents was clearly shown by the average 

composition of their progeny and by the characteristics of the frequency 

distributions of ß–pinene and 3-carene (table 5-6, fig. 5-16). For ß–pinene the 

progeny of WP-3301 had a large mode near zero with a few scattered 

measurements up to about 75 percent and an overall average of about 23 

percent. For ß–pinene, the progeny of WP-B475 had just a few measurements 

near zero with three distinct modes between about 39 percent to about 80 

percent with an overall average of 44 percent. For 3-carene the reverse was true. 

The progeny of WP-3301 had a mode at 0 percent and three modes between 15 

percent to 85 percent and an average of 45 percent, whereas the progeny of WPB475 had a mode at 0 percent with a few scattered measurements between 12 

percent and 60 percent and an average of 15 percent. Both sets had the 

camphene anomaly at 6 years. The presence of a small zero mode for 3-carene 

in the progeny of WP-3301, where none would be expected, and for ß–pinene in 

the progeny of WP-B475 might be explained by the action of the juvenile factor 

or by isomerization. There could be a trend in the age series of limonene (fig. 5-

15) toward a smaller number of trees at or near 0 percent with increased age, 

though the sample numbers were small. This could mean that the juvenile 

effect is decreasing with a resulting increase in limonene. 

The characteristics of the frequency distribution for limonene were quite 

similar for both the time of growth sets (fig. 5-15) and for the aggregate sets (fig. 

5-16): one mode at or near 0 percent with other measurements extending from 

about 8 percent to about 25 percent but with a couple of measurements near 40 

percent. With a (0-0) set of alleles for limonene in the parents, one would expect 

a mode at or near 0 percent and a second mode around 20 and 30 percent, 

reflecting some alleles for limonene in the wind pollen source. The failure of the 

second mode to be larger was attributed to the juvenile effect. This same 

238 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-I4—Comparative frequency 

distribution of the amount of the noted 

monoterpenes in the progeny of two P. 

ponderosa with similar composition,WP3293 and WP-B477, aggregated for 4 to 

11 years of nursery growth and 4 years 

of container growth; each dot is measurement of one tree; [s] is average of set. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 239 
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

240 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-I5—Comparative 

frequency distribution of the 

amount of the noted monoterpenes in the progeny of two P. 

ponderosa with dissimilar composition, WP-3301 and WPB475, for the four periods of 

nursery growth listed on the 

right; each dot is measurement 

of one tree; [ ▲ ] is average of 

set. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 241 
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

242 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 243
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

244 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 245
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-16—Frequency distribution of the amount of the noted

monoterpenes in the progeny of two

P. ponderosa with dissimilar composition, WP-3301 and WP-8475, aggregated for 4 to 12 years of nursery 

growth; each dot

 iindicates each is 

is measurement of 

one tree; where 

n trees; [ ▲ ] is average of set. 

246 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

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Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

condition, i.e., lack of an expected mode greater than 20 percent for limonene, 

was found for other sets of progeny. There was a possible indication in the age 

series (fig. 5-15) that the 12-year-old trees may be starting to overcome this 

juvenile effect. 

Trees WP-3359 and WP-3318 

The two parents differed appreciably in all major components as follows 

respectively for WP-3359 and WP-3318: α–pinene, 13 vs. 27 percent; ß–pinene, 

31 vs. 10 percent; 3-carene, 42 vs. 18 percent; limonene, 1 vs. 40 percent (table 5-

5). The composition of the progeny paralleled this pattern (table 5-6). There was 

some shifting in composition over time in the progeny of WP-3359 (fig. 5-17), 

but this could be attributed to the small number of samples at the later years. 

The two sets of progeny also differed in the characteristics of the frequency 

distributions of the aggregate populations for α–pinene, ß–pinene, 3-carene, 

and limonene (fig. 5-18). 

The progeny of WP-3359 in the age sets (fig. 5-17) showed the same trend 

for limonene at 12 years (as noted earlier for the progeny of WP-3301 and WPB475) for a decrease in the number of trees with near-0 percent and an increase 

in larger values from 10 percent to 50 percent. This again suggested a weakening 

of the juvenile effect at about 12 years. 

Trees WP-3292 and WP-3293 

The two trees differed sharply in ß–pinene, 76 vs. 11 percent, and in 3-carene, 0 vs. 

76 percent (table 5-5). Both trees were very low in limonene. These differences 

are reflected in the composition of their progeny (table 5-6). There were 

insufficient data to determine composition shift over time in the progeny. As 

expected, the frequency distributions were very different for b-pinene and 3-

carene (fig. 5-19). The progeny of WP-3292 had no mode for b-pinene near zero 

and had two or three modes between 25 and 80 percent; WP-3293 had a mode at 

zero with a scattering of measurements up to about 55 percent. For 3-carene the 

pattern was reversed; WP-3293 had a mode of zero with two or three modes 

between 20 and 80 percent. The frequency distributions for limonene were similar, 

a mode at zero and a scattering of values up to about 15 percent. Again, the lack of 

measurements above 20 percent for limonene was attributed to the juvenile effect. 

This condition had been noted previously for other sets of progeny. 

Multiple-Tree Comparisons 

Trees WP-3298, WP-3352, AS-3139 

These three trees, classed as high limonene, had about the same composition. 

One could postulate that they had the same assigned structure of alleles: (0-1), 

(0-0), (0,0), (0-0), and (1-1), respectively, for α–pinene, ß–pinene, 3-carene, 

myrcene, and limonene. However, WP-3298 and WP-3352 were growing at 

Wheeler Peak in the Escalante North Transition Zone with background pollen 

of 15 percent limonene, while AS-3139 was at Adin Summit in the Sierra Pacific 

Region with background pollen of 13 percent limonene, suggesting that alleles 

for limonene were a bit more abundant at Wheeler than at Adin. Comparison of 

the progeny of the three trees could be helpful in understanding the background 

pollen as well as the effect of the place of growth of the progeny and the 

geographic location of the parent. 

There was no large shift in any component with the age of nursery growth 

(as noted previously in the discussion for each set of progeny), at least not of 

the magnitude found in the progeny of the Ranger Peak parents. This could be 

a unique characteristic of the Ranger Peak progeny, or it could be caused by the 

location of the type of parent trees; i.e., Ranger Peak parents had large amounts 

of ß–pinene and low or no 3-carene. However, it was clear that the progeny of 

248 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
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th Population Studies of the Monoterpene Composition Chapter 5 

of 4-to 12-Year-Old Half Siblings of P. ponderosa 

the Wheeler Peak trees were suitable for comparative analysis at ages 4 to 12 

years, though there was still some juvenile effect. 

A comparison of the frequency distributions of the components of the 

progeny of the three trees follows (fig. 5-20). α–pinene: The progeny of WP-3298 and WP3352 were q

uite similar. The 

distribution was multimodal with one large mode at about 15 percent and two 

or more modes between 20 percent and 80 percent. The progeny of AS3139 

were somewhat different, with one very large mode at about 15 percent and a 

very small mode at about 20 percent. This suggested that there were many 

more trees at Wheeler than at Adin, with a (0-1) or (1-1) set of alleles for α– 

pinene. That is, there were more alleles for α–pinene in the pollen at Wheeler 

Peak. 

Camphene: Trees WP3298 and WP3352 were very similar in amount and 

distribution of camphene and both differ slightly from AS-3139 in the 

distribution pattern, suggesting a minor genetic difference in camphene 

between the two Wheeler trees and AS-3139. 

ß–pinene: All three distributions were somewhat similar with one large 

mode near 2 percent and two or more modes between 2 and 75 percent. This 

suggested that the alleles for ß–pinene were about the same in both localities. 

However, since there can be only one allele for ß–pinene in the progeny—none 

of the parents had an allele for ß–pinene—the 0-1 set for ß–pinene can produce a 

large amount of ß–pinene when a-pinene and limonene were low because of the lack of competition for the precursor, and because the juvenile effect seems 

to be expressed more strongly by ß–pinene. 

3-carene: The distribution of 3-carene was quite different between the two 

places of growth of the trees. Since there was no 3-carene in any of the three 

parent trees, one would expect a distribution like that of the progeny of AS-

3139, one mode at or near 0 percent and a second mode near 30 percent. The 

distribution for the progeny of WP-3298 and WP-3352 had the expected mode 

at or near 0 percent and possibly two broad modes between 15 percent and 75 

percent. There could be a difference in the allele structure between the two 

localities, though not likely, or there was a difference in the response of the 

seedlings to the place of growth: progeny of AS-3139 were growing "in" their 

resin region while the progeny of WP3298 and WP-3352 were growing "out" 

of their region. I would postulate that it was the place of growth of the seedlings. 

Also, there could be a difference in a minor genetic structure between Wheeler 

and Adin, but such a structure has not yet been found. 

Myrcene: The distributions for myrcene were quite similar for all three 

trees with one large mode at about 5 percent and a much smaller one at about 

15 percent. This suggested that alleles for myrcene were present but rare at 

both localities. An allele for myrcene did not show up in any of the controlled 

breeding with the Wheeler Peak trees. 

Limonene: The distributions of the progeny of the two Wheeler trees were 

quite similar but somewhat different from that of the Adin progeny. It could 

well be that when there was an allele for α–pinene in young trees, such as was 

likely in the progeny of the two Wheeler trees, the activity of the limonene 

alleles was greatly depressed because of the juvenile factor. This condition 

could account for the difference between the progeny of the two Wheeler trees 

and the progeny of the Actin tree in the frequency distribution of limonene. 

That is, the greater frequency of alleles for α–pinene at Wheeler Peak caused 

the differences between Wheeler Peak and Adin Summit progeny in both α– 

pinene and limonene, with greater α–pinene and lesser limonene at Wheeler 

Peak. There could also be an effect of locality of growth and differential 

response to the juvenile effect, or of a minor genetic structure. 

The progeny of these three trees were sharply different from that of the 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 249 
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-17—Frequency distribution of 

the amount of the noted monoterpenes 

in the progeny P. ponderosa WP-3359, 

with four ages of nursery growth listed 

on the right; each dot is measurement of 

one tree, [ ▲ ] is average of set. 

250 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 251
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-18—Comparative frequency 

distribution of the amount of the noted 

monoterpenes in the progeny of two P. 

ponderosa with dissimilar composition, 

WP-3359 ad WP-3318; each dot is measurement of one tree; [▲] is average of 

set. 

252 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

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Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-19—Comparative frequency distribution of the amount of the noted

monoterpenes in the progeny of two P. ponderosa with dissimilar composition, WP-3293 

and WP-3292; each dot is measurement of

one tree; except where 

n trees; [ ▲ ] is average of set. 

indicates each is 

(continues on next page) 

254 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
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of 4- to 12-Year-Old Half Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 255
Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-20—Comparative frequency distribution of the amount of the noted monoterpenes in the progeny of three high limonene P. 

ponderosa, WP-3298, WP-3352, and AS-3139; 

each dot is measurement of on

average of set. 

e tree except 

where indicates each is n trees; [▲] is 

(fig. 5-20 continues on next 3 pages) 

256 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
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of 4- to 12-Year-Old Half Siblings of P. ponderosa 

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th Population Studies of the Monoterpene Composition Chapter 5 

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progeny of RP-B37, the high-limonene tree at Ranger Peak, in the amount and 

distribution of limonene. Despite the fact that Ranger Peak had background pollen of about 22 percent limonene, the progeny of RP-B37 was only 17 percent limonene, with very few values above 20 percent. This could be caused by the greater frequency of alleles of ß-pinene at Ranger Peak plus the apparent 

greater effect by ß-pinene on the juvenile condition of the young progeny. 

However, there was an ultra-high limonene progeny of RP-B37. 

Trees WP-3298, WP-3352, WP-3299, WP-3312 

All four trees growing at Wheeler Peak were classed as high or near-high 

limonene—and each was assumed to have a (1-1) set of alleles for limonene— 

and all had wind-pollinated progeny that were high limonene or potential high 

limonene. They differed in that WP-3299 and 3312 had substantial 3-carene. 

The characteristics of the frequency distributions of the individual components 

of the progeny were generally what would be expected from the parental 

composition and the background pollen (fig. 5-21). However, there were some 

differences that suggested a differential effect of the juvenile factor, which 

depends on composition, on the effect of growth of a tree outside its ecosystem, 

and possibly on a minor genetic system. Not surprisingly the two highlimonene trees, WP-3298 and WP-3352, had the most progeny of the high or potentially high-limonene type. 

For comparative analysis of the relationship of limonene to the frequency 

distribution of the other monoterpenes, three generalized types of composition 

were considered potentially high limonene: (1) those with greater than 20 

percent limonene, (2) those with less than 20 percent ß-pinene plus 3-carene, 

and (3) those meeting both requirements (table 5-9). The data for the progeny of 

the four trees were separated into the three groups on the basis of the conditions 

just stated. The average composition for the progeny in each of the three groups 

for each of the four parent trees was very similar, and their frequency 

distributions were also very similar (fig. 5-19). 

The following is a discussion of some aspect of these three generalized 

types of composition. 

(1) When limonene was greater than 20 percent (fig. 5-21a) 

The frequency distributions for all components were somewhat similar for 

the progeny of all four trees when limonene was greater than 20 percent. 

α-Pinene: Average α-pinene varied somewhat among the four sets of 

progeny, but the configurations of the distributions are similar. Each 

distribution had a mode at about 10 percent, another between 15 and 20 

percent, and a third one near 40 percent. It was speculated that the first mode 

was caused by isomerization or by some activity by the (0-0) set of alleles. 

ß-Pinene: All four sets of progeny had a large mode at about 2 percent, 

probably caused by isomerization. Trees WP-3298, WP-3352, and WP-3312 had 

a few scattered values greater than 10 percent while WP-3299 had two distinct 

modes between 15 and 40 percent despite the lack of ß-pinene in the parent 

tree. Because these were wind-pollinated progeny and the parent tree had 

essentially no ß-pinene, it was difficult to say why the progeny of WP-3299 

were so different from the other three trees. 

3-Carene: Here again WP-3298, WP-3352, and WP-3312 were quite similar 

with one mode at about 1 percent and two other modes further up the percent 

scale. But WP-3329 had no mode below 10 percent although it did have two 

modes between 24 and 60 percent; this suggested a (1-1) set of alleles for 3-

carene in WP-3299. 

Myrcene: There was a general similarity among the four sets of progeny 

with a large mode near 3 percent and two much smaller modes further along 

the percent scale. Thus, none of the four trees had an allele for myrcene, and 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 259 
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Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Table 5-9—Average xylem monoterpene composition of three classes of the wind-pollinated progeny of four trees at Wheeler Peak. N = number of trees. 

Tree Class of N 

compositor Monoterpene1 

α-p cam ß-p car my lim ß-ph ter 

- --percent

2

-- -

3298 3 50 29.9 0.5 3.9 

3352 52 20.5 0.2 5.7 

3299 52 11.3 0.6 12.6 

3312 32 17.8 0.5 8.0 

3298 4 54 64.5 0.6 3.6 

3352 35 56.5 0.l 4.5 

3299 2 76.4 0.0 3.7 

3312 15 64.0 0.3 2.7 

3298 5 24 49.4 0.7 2.4 

3352 17 40.7 0.1 3.7 

3299 0 

3312 6 46.5 0.5 2.3 

24.1 5.9 34.7 0.1 1.0 

31.8 5.7 34.2 0.4 1.2 

37.8 3.4 31.9 1.9 1.6 

36.5 3.9 31.4 0.2 1.6 

0.7 8.6 21.9 0.1 0.0 

0.6 12.2 25.4 0.6 0.1 

0.2 0.0 19.4 0.2 0.0 

0.4 12.6 19.6 0.2 0.0 

1.3 8.3 37.8 0.1 0.1 

0.7 8.7 45.7 0.3 * 

0.5 6.6 43.6 0.2 0 

1

α-pinene, camphene, ß-pinene, 3-carene, myrcene, limonene, ß-phellandrene, terpinolene. 2-Normalized; * = trace. 2

When limonene was equal to or greater than 20 percent. 4

When ß-pinene and 3-carene was less than 20 percent. 5

When conditions of both 3 and 4 were met. 

260 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-21—Comparative frequency distribution of the amount of the noted 

monoterpenes in the progeny of four P. ponderosa that were suspected of having a (1-

1) set of alleles for limonene, WP-3298, 

WP-3352, WP-3299, and WP-3312, when 

progeny were grouped into classes: (a) 

greater than 20 percent limonene (21 a), (b) 

ß-pinene plus 3-carene less than 20 percent 

(21 b), and (c) progeny meeting both condit

one tree, except where 

ions (21c); each dot is measurement of 

indicates each is 

n trees. [▲] is average of set. 

(fig. 5-21 continues through page 269) 

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Chapter 5 Population Studies of the Monoterpene Composition Smith 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

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of 4- to 12-Year-Old Half Siblings of P. ponderosa 

they simply reflected the general level of pollen, or the same level of 

isomerization or production of biosynthetic by-products. 

Limonene: Here again, all four were similar, with a large mode between 24 

and 35 percent, which almost tended to be bimodal, and another mode above 

35 percent. The smaller mode further along the scale could have been caused by 

these trees beginning to overcome the juvenile effect and had reached the start of 

"mature" status of monoterpene synthesis. Likewise, it can be speculated that all 

the trees in this classification could shift to the highest mode in future years. 

(2) When ß-pinene plus 3-carene was less than 20 percent (fig. 5-21b): 

When this condition was met, all four sets went to high α-pinene. This was 

assumed to be caused by the juvenile factor. However, WP-3299 and WP-3312 

had very few progeny in this class; i.e., ß-pinene plus 3-carene was less than 20 

percent. Because each parent had, apparently, alleles of ß-pinene, 3-carene, or 

both, the progeny will usually have considerable amount of both. The general 

distributions were somewhat similar for ß-pinene and 3-carene. The 

distributions for myrcene and limonene were quite similar for all four sets of 

progeny when the unequal numbers in the sets were considered. Limonene had 

a multimodal distribution, but the number of modes is not clearly defined. 

(3) When limonene was greater than 20 percent and ß-pinene plus 3-carene was 

less than 20 percent (fig. 5-21c): 

The lack of more trees in this class limited conclusions. However, the 

tendency for high α-pinene was considered to be caused by the juvenile effect. 

In general, though, the distributions were somewhat similar. 

Trees WP-3292, WP-3293, WP-3294, WP-3318, WP-B477 

There were fewer than 35 progeny for each of these five trees, and they will be 

treated as one diverse unit to contrast the females. The frequency distributions 

of individual monoterpenes were developed (fig. 5-22) along with the average 

of the set, the composition of the female parent, and the stand average at 

Wheeler Peak to represent the composition of the background pollen. The 

following observations were made about the average composition with respect 

to the female parent and the stand average (table 5-10): 

α-pinene was usually a bit higher in the progeny than in the female parent 

though it was usually close to the stand average. The progeny of WP-3318 were 

an exception to this, but this reflects the much higher α-pinene in WP-3318 than 

in the stand. 

ß-pinene was almost always higher in the progeny than in the female 

parent or the stand, except for WP-3293 which was 76 percent ß-pinene in the 

female, a very high amount. 

3-carene was either higher or lower in the progeny than in the stand, 

probably because of irregular response to the juvenile effect. 

Myrcene was always lower in the progeny than in the female or the stand. 

Limonene was always lower in the progeny than in the female or the stand. 

The aggregate of these observations showed that the juvenile effect results 

in greater ß-pinene and less myrcene and limonene in progeny, that 3-carene 

did not seem to be affected by the juvenile factor, and that α-pinene probably 

increased in the progeny. 

Trees WP-3298, WP-3352, WP-3299, WP-3312, WP-B475, WP-3301, WP-3320, 

WP-3359 

All eight trees had a total sample size of more than 70 progeny per parent tree, 

which was, therefore, sufficient for comparison of frequency distribution of 

each of the eight components (fig. 5-23). The very large range in the amount of 

the major components—α-pinene, ß-pinene, 3-carene, myrcene, limonene— 

264 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
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of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-22—Comparative 

frequency distribution of the 

amount of the noted monoterpenes in the progeny of P. ponderosa WP-3292,WP-3293,WP3294, W P-33 18, W P-B477; each 

dot is measurement of one 

tree;[ ▲ ] is average of progeny set; ○ = composition of parent tree; ↓ is 80-tree stand 

average. 

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of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Table 5-10—Differences in the average amount of five major monoterpenes

1 between progeny and female parent and between progeny and 

stand average at Wheeler Peak 

Progeny of Direction2

 of amount in progeny from amount in: 

female for stand for 

α-p ß-p car myr lim α-p ß-p car myr lim 

WP-32923 o + + - + + + - - -

WP-3293 + + - - + + o + - -

WP-3294 + + + - - + o + - -

WP-3318 - + + - - + + - - -

WP-B477 + + o - + + + + - -

1

α-pinene, ß-pinene, 3-carene, myrcene, limonene. 2

-= progeny less than female or stand. 

+= progeny greater than female or stand. 

o = progeny about same as female or stand. 3

very low limonene.s 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 273 
Chapter 5 Populati

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of 4-to 12-Year-Old Half Siblings of P. ponderosa 

was readily apparent. A strong tendency for multimodal distributions, 

generally trimodal, was discernible in many distributions; this supported the 

hypotheses of two additive alleles at a single locus for each major monoterpene. 

The narrow mode between 0 and 2 to 3 percent for ß-pinene, 3-carene, myrcene, 

and limonene was presumed to be caused by isomerization or biosynthetic by-

products, by a minor genetic structure, or by a slight bit of activity by the (0-0) 

set of alleles. The larger near-0 percent mode for α-pinene could be a mix of the 

above or activity by the (0-0) set of alleles. There was a strong tendency for α­

pinene to have a double mode between 0 to 20 percent which suggested that all 

the mechanisms noted above may operate. Therefore, in general, the differences 

in the composition of the female parent was reflected in the composition and 

frequency distribution of its wind-pollinated progeny and the general 

background pollen. However, it was readily apparent that the level of myrcene 

and limonene in progeny was well below the level of the parent tree, that the 

level of α-pinene and ß-pinene was generally well above the parent except 

where the level in the parent tree indicated a (1-1) set of alleles in the parent, and 

that the level of 3-carene was about at the level of the parent or slightly below. 

This condition was presumed to be caused by the juvenile factor or the stress of 

growing far beyond its seed source and resin zone, or both. With age, these levels 

may slowly move toward the expected ones. Nevertheless, these data were 

adequate for comparative purposes. It was also readily apparent that the level of 

one component could affect the level of one or more of the other components. 

Types of Composition 

Thirty-seven types of composition were found among the progeny of the 13 

parents (fig 5-24). The primary objective of the study was to produce trees with 

a large and diverse array of compositions; this was clearly accomplished. Types 

with large amounts of limonene were, as expected, found among the progeny 

of parents classed as high or near-high limonene. The ultra-high type was 

expected and two were found; both were progeny of WP-3352. These two were 

of note because they were very much like the ultra-high types found in the 

progeny from Ranger Peak (fig. 5-4) and Adin/Placerville (fig. 5-6). There were 

no ultra-high types among the progeny of WP-3298, when such was expected. 

This ultra-high type also resembled the composition of P. torreyana (see Chapter 

3, #18) except that P. torreyana had small amounts of nonane and undecane. 

There were several types of composition that had not yet been found in natural 

stands. Were these types valid, or artifacts of the effects of stress and of the 

juvenile factor, or are they valid and will not survive the environmental 

pressures by maturity? The types of composition also show the very large 

range in the amount of the five major components: α-pinene 3 to 89 percent, ßpinene 0 to 91 percent, 3-carene 0 to 86 percent, myrcene 1 to 50 percent, 

limonene 0 to 86 percent. 

Discussion: Half-Siblings P. ponderosa 

Young progeny from Ranger Peak, Adin Summit, and Wheeler Peak had a 

somewhat different composition than would be expected from the composition 

of the female parent and the general background pollen. This difference was 

primarily attributed to a juvenile effect that was expressed by an increase in ßpinene and α-pinene and a decrease in myrcene and limonene with 3-carene 

either unaffected or inconsistent. Likewise, the juvenile effect was most evident 

in stands where ß-pinene or α-pinene or both were high, much as in the stand at 

Ranger Peak. Because of the changing juvenile effect, half-siblings from Ranger 

Peak were not as useful as anticipated in understanding monoterpenes, but the 

results were quite helpful in guiding studies of progeny from Wheeler Peak 

and Adin/Placerville. 

274 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-23—Comparative frequency 

distribution of the amount of the noted 

monoterpenes in the progeny of the 

eigh

on the right; each dot is measurement 

t female parent P. ponderosa listed 

of one tree except where indicates 

each is n trees; [▲] is average of set; 

↓ is 80-tree stand average. 

(fig. 5-23 continues on the next 7 pages) 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 275 
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of 4- to 12-Year-Old Half Siblings of P. ponderosa 

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of 4- to 12-Year-Old Half Siblings of P. ponderosa 

Figure 5-24—Thirty-seven types of monoterpene composition 

in the progeny of the 13 female parent P. ponderosa at Wheeler 

Peak, their average composition, minor components omitted, and 

their relative occurrence in each half-sibling family; [●] occurs 

commonly; [ ○] occurs not commonly. 

Type Monoterpene1 

# α-p ß-p car my 1im 

1 11 0 0 3 83 ○ 3298 3352 

3299 3312 3474 3301 3320 3359 3292 3293 3294 3318 

ß-477 

2 35 2 1 4 59 ○ ○ ○

3 4 0 39 4 50 ○ ○ ○

4 32 6 1 15 47 ○ ○ ○

5 32 14 1 13 40 ○

6 7 21 31 3 37 ○

7 56 2 1 10 30 ● ●

8 8 1 54 9 27 ● ● ○ ○ ○

9 71 2 0 0 25 ○ ○ ○ ○

10 9 59 0 6 25 ○

11 7 34 34 4 20 ● ● ● ●

12 20 8 45 4 19 ● ● ○

13 25 47 8 3 16 ● ●

14 9 20 49 5 15 ○

15 14 73 0 11 11 

16 8 1 61 15 11 ○

17 11 44 28 4 11 ● ●

18 10 39 41 1 9 ● ●

19 6 32 48 3 7 ● ● ●

20 89 0 0 4 7 ● ● ○

21 20 45 47 1 7 ● ○

22 13 57 24 1 4 ● ● ● ●

23 17 73 0 6 2 ● ○ ○

24 39 32 22 4 1 ● ●

25 4 51 20 25 1 ●

26 23 28 41 4 1 ● ●

27 10 0 76 9 0 ● ● ○ ○ ● ● ○ ●

28 57 4 0 33 0 ○

29 35 58 0 5 0 ● ● ● ●

30 7 91 0 1 0 ●

31 34 2 60 4 0 ● ● ●

32 3 11 86 1 0 ● ●

33 46 13 1 38 0 ○

34 80 0 0 20 0 ● ● ○ ● ○

35 70 0 26 4 0 ○

36 52 22 26 0 0 ○

37 43 6 0 50 0 ○

1

α-pinene, ß-pinene, 3-carene, myrcene, limonene 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 283 
Chapter 5 Populati

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of 4-to 12-Year-Old Half Siblings of P. ponderosa 

The juvenile effect was present in the progeny of trees from Adin Summit 

and Wheeler Peak, but did not seem as strong as at Ranger Peaks. There was 

little change in composition during 12 years of nursery or container growth. 

Therefore, the data on these trees was considered adequate for statistical 

analyses. There was some slight evidence that the juvenile effect was weakening 

at 12 years. 

The primary objectives of the study were to produce a diverse array of 

compositions of monoterpenes for studies of host resistance and for 

monoterpene studies; the results clearly showed that this objective was 

achieved. It was also quite clear that the quickest and most economical 

procedure to obtain such trees, including high limonene trees, would be to 

establish a plantation of wind-pollinated progeny of high- and near-high 

limonene parent trees from an area with a wide range of compositions in the 

native stand, such as Wheeler Peak or Adin Summit. For efficiency of land 

space, such a plantation could be planted at a 3-ft by 3-ft spacing, sampled for 

resin at 8 or 10 years, and then thinned to about a 6-ft by 6-ft spacing to obtain a 

residual stand with desired compositions. A controlled breeding program, as 

will be shown later in the discussion of full siblings, can achieve the same 

objectives with greater predictability but requires longer time and at a much 

greater cost. The chance of getting ultra-high limonene is much greater with 

controlled breeding. 

The variety and range of the composition types found in the study and of 

the range of the frequency distribution of individual components were much 

greater in the aggregate of the progeny than in the natural stand, and the 

question might be raised about such difference, particularly when one 

considered the small number of parent trees in the study (and these were 

chosen largely on the basis of high and low limonene). Two answers come to 

mind. (1) The compositions were a juvenile state of the progeny population, 

and before maturity the individual tree compositions will slowly change with a 

resulting decrease in the variety of compositions. (2) Many types, by themselves or in conjunction with related tree characteristics, will not survive. 

There were some indications again that the amount of ß-pinene could be a 

major factor for the variation and instability in the composition of young 

seedlings, either by itself or in conjunction with other conditions. 

There was considerable evidence in these studies of 4- to 12-year-old halfsiblings of P. ponderosa that the quality and quantity of the xylem monoterpenes 

were under strong gene control. The composition of the half-sibling progeny of 

parents with similar composition was very similar in both averages and in the 

configuration of the frequency distribution of individual components; the 

composition of half-sibling progeny of parents with dissimilar composition 

was different, but predictably so, considering the parent composition and the 

stand average composition that was the presumed composition of the pollen 

parents. However, several conditions can modify monoterpene composition as 

follows: (1) stress from the over application of a phytocide, (2) stress of 

prolonged growth in restrictive containers, (3) the juvenile period of growth, 

(4) stress of rapid growth, (5) the actual composition of the tree itself, 

particularly large amounts of α-pinene and ß-pinene, (6) interactive competition 

among components for a fixed amount of biosynthetic precursor, (7) 

isomerization, (8) biosynthetic by-products, (9) growing far from the seed 

source, (10) and the possibility of a minor genetic structure. The possible action 

of these conditions separately or in concert dictates the use of a large number of 

samples and the maintenance of studies for extended periods. 

The multimodal characteristics of the frequency distributions of individual 

components taken as a whole strongly suggested that the primary genetic 

structure for monoterpenes in P. ponderosa xylem resin is a pair of additive 

alleles at a single locus for each of the five major monoterpenes: α-pinene, ß284 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Population Studies of the Monoterpene Composition Chapter 5 

of 4- to 12-Year-Old Half Siblings of P. ponderosa 

pinene, 3-carene, myrcene, and limonene. However, the amount of these major 

monoterpenes can be modified considerably by the juvenile effect and by stress 

factors noted above. And there may be a minor genetic structure that might be 

associated with the geographic source of the tree, but such a structure has not 

been resolved, if it does exist. Also, these major components might possibly be 

produced in small quantities by either isomerization or biosynthetic byproducts. Minor components were also probably produced largely by the same 

two factors. Myrcene was considered a major component because it did occur 

at a sufficient percentage, though infrequently; it usually occurred in minor 

component amounts. 

When a parent was grown in two locations more than 200 miles apart but in 

the same resin ecotype regions, the compositions of the two sets of progeny, 

i.e., one set from the parent at each location, were nearly identical. 

The compositions of the half-sibling progeny from two different high 

limonene parents, having very similar composition and growing in two 

different resin ecotype regions, were still different enough to raise the questions 

of the differential effect of the two localities, the possibility of a minor genetic 

system, or the growth of one set of progeny more than 400 miles from its source 

and in a different ecotype region. 

The incidence of an unusually large amount of camphene (2 to 4 percent), 

considered a minor component, in the 6th year of growth in the progeny of 

most trees, was considered an anomaly. This anomaly occurred in different 

calendar years of the study and in various nursery plantings but always during 

the 6th year of growth. It was possible that the anomaly may not be camphene 

but some unknown, transient chemical which chromatographs as camphene, 

though all the GLC evidence points to camphene. This anomaly was not large 

enough to measurably change any of the major monoterpenes or their analysis. 

A type of composition called ultra-high limonene was found among the 

progeny of the three high-limonene trees used in the study, RP-B37 at Ranger 

Peak, AS-3139 at Adin Summit, and WP-3352 at Wheeler Peak. This type of 

composition was not at all common in the study and had not yet been found in 

natural stands. Whether any exist is not known; and "if not, why not," were 

unanswered questions. Types with high limonene, as expected, were found 

among the progeny of high limonene parents, including the three noted above 

as well as in the progeny of WP-3298, WP-3312 and WP-3299. 

No marked change in quantitative composition was found with increase in 

age from 4 to 12 years. Thus the data were suitable for analyses and inference 

on a comparative basis but not on an absolute basis. (It appears that the age 

phenomenon found in the Ranger Peak progeny may be restricted to that 

locality or the types of composition found in that locality.) However, a juvenile 

effect was present in the Wheeler progeny, but this did not affect analysis. It is 

postulated that there will be a slow change over many years to the composition 

of the mature tree. This juvenile effect seemed to be manifested in an increase in 

α-pinene and ß-pinene and a decrease in myrcene and limonene. These same 

changes seemed to be associated with various forms of stress. Thus one might 

postulate that all young pines are under some degree of stress which might be 

called the stress of rapid growth. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 285 
CHAPT

ER 6 

Monoterpene Composition of Populations 

of 4- to 11 -Year-Old Full Siblings of 

P. ponderosa 

Summary: Fifty-six sets of full-sibling populations of P. ponderosa were derived 

from combinations of seven females and 14 males. Forty-two sets of progeny had 

sufficient numbers for modal analysis of the frequency distribution of individual 

monoterpenes. In all cases the actual number of modes derived from the analysis 

equalled or exceeded the number of modes expected, based on the assignment of 

additive alleles to the two parents. In about the remaining half of the analyzed 

distributions the actual number of modes was the same as the expected. This 

result supported the additive allele hypothesis for the five major monoterpenes 

in P. ponderosa -α-pinene, ß-pinene, 3-carene, myrcene, and limonene; myrcene, 

though, appears to be a rare allele. Where both parents were assigned a (0-1) set of 

additive alleles for a given monoterpene, the ratio of the size of the low-middlehigh modes was generally about 1:2:1, the predicted ratio; this was additional 

support to the hypothesis and to the assignment of alleles. 

Fifty-eight types of monoterpene composition were found in the full array of 

56 families. High limonene trees always bred true, but a juvenile effect was 

clearly evident in the progeny and was evidenced by an increase in α-pinene and 

ß-pinene and a decrease in limonene and myrcene. Other combinations of 

parents also produced high limonene progeny. Some progeny could be 

classed as ultra-high limonene (80 to 90 percent), a type of composition not yet found in natural stands. Other types of composition were found among 

the progeny which have not yet been found in natural stands. The large 

variation of composition of a single set of progeny suggested the effects of 

several nongenetic factors on the basic genetic structure, as well as the 

effects of interactions within the basic genetic structure for the synthesis of 

monoterpenes. 

There was a noticeable difference between the progeny of a female with two 

males, one that was near and one that was far from the female. This was 

evidenced in much the same way as the effects of stress, and it was postulated 

that there was a level of stress in the progeny of parents which were far apart, or 

"off-site." The effects of several forms of stress were clearly evident in full 

siblings, and were often greatest in high limonene trees, and where parents were 

far apart. 

Breeding on grafts produced the same array of progeny as breeding on the 

parent tree of the graft. Over an 8-year period there were no sharp shifts in the 

composition of sets of the same progeny in a given location, indicating that 

changes will be slow over many years: α-pinene and ß-pinene decreasing, 

myrcene and limonene increasing, and 3-carene increasing or decreasing 

depending on the composition. An increase in camphene and ß-phellandrene 

with age was postulated. 

All observations were based on sampling different sets of trees from the 

same seed lot and not on resampling the same set of trees. There was no 

incompatibility between the various parent trees. Reciprocal crosses showed 

equal contribution by male and female. 

The assumption that the quality and quantity of xylem resin monoterpenes of 

P. ponderosa were strongly fixed by a genetic mechanism gradually worked its 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 287 
Chapter 6 

Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

way into the literature. This assumption appeared to have been strengthened 

by its repeated use in the literature, often without much supporting research 

evidence. The assumption probably gained much support when Mirov (1961) 

reported very little change in the composition of P. ponderosa xylem 

monoterpenes over short periods of 3 to 5 years. In that same report, Mirov 

noted that the composition of pine hybrids was, generally, intermediate to the 

parents and that the composition of trees planted far from the seed source was 

similar to the trees at the source. More recently, composition was shown to be 

very constant in mature P. ponderosa with respect to radial, horizontal, and 

longitudinal position in the tree and with time (see Chapter 8 this volume). 

Controlled breeding of seven female P. ponderosa with from 5 to 12 pollen 

sources each was conducted. The composition of all trees was listed, and a preliminary assignment was made of the alleles for the five major monoterpenes 

in each tree based on the monoterpene composition (table 6-1). The basic 

objectives of the breeding were: (a) to determine if a supply of high limonene 

trees could be conveniently established at the USDA Forest Service's Institute 

of Forest Genetics, Placerville, Calif., for testing the effects of limonene on the 

success or failure of the attacks of D. brevicomis on P. ponderosa, and (b) to 

develop a research supply of trees with a diverse array of xylem monoterpene 

compositions at IFG for elucidating the genetics and variation of monoterpene 

composition. The discussion was organized around the seven female trees. 

A wide selection of parent tree compositions seemed desirable for the 

breeding study because the action of a number of competing or interacting 

alleles and the effects of several nongenetic factors caused increased variation 

in composition. A good selection of parents, though heavily slanted to trees 

with higher limonene, was used; on hindsight, an even wider selection would 

have been desirable. However, the trees used were the best that could be 

obtained under the operational and fiscal constraints of the study. 

Parent trees at Adin Summit were resampled at different locations on the 

tree and at different times in order to determine if the compositions were 

constant through time and space, or if the unusual compositions were spurious 

and invalid as others had claimed. 

Breeding was carried out from 1972 to 1980. Trees that served as females 

were located at Adin Summit and at IFG; and grafts of Adin Summit trees, now 

growing at IFG, also served as female trees (fig. 5-1). Twenty or more grafts 

were attempted for several of the key trees at Wheeler Peak, the source of many 

of the pollen parents, but none survived. This failure prevented the desirable 

reciprocal crosses. The first efforts to collect pollen from the Wheeler Peak trees 

failed in 1970 because of improper timing. It was later found that the time and 

characteristics of catkin development were quite different at Wheeler Peak in 

eastern Nevada than on the western slopes of the Sierra Nevada in California. 

But a good supply was obtained in 1971 for use in 1972, and afterwards, when 

conelets were first available at Adin Summit. No pollen was collected from the 

high limonene tree at Ranger Peak (see Chapter 5), and unfortunately no 

breeding was done with this tree. 

Adin Summit was an interesting and valuable study area. It had two high 

limonene trees, four trees with a large amount of limonene—but not enough to be 

classed as high limonene—and one tree with only an average amount of limonene. 

One of the high limonene trees was found in the original 80-tree stand used in the 

regional study of P. ponderosa. Two additional high limonene trees were found in a 

later sampling of 1600 trees in the area. Thus, on the average, there was one high 

limonene tree per about 500 in the area; yet, quite fortuitously, one such tree was 

found in the original 80-tree sample. Several near-high limonene trees were also 

found in the later sampling of 1,600 trees at Adin Summit. 

The procedure for controlled pollination was that generally employed by 

IFG for all pines and is briefly described as follows (Anonymous 1948, 

288 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa

Table 6-l—Xylem monoterpene composition of the 16 listed P. ponderosa used as parents in the controlled pollination program, their 

diameter in inches, and the preliminary assignment of additive alleles to them for the major components 

Monoterpene1 Assigned alleles2 

Tree no. α-p cam ß-p car myr lim ß-ph ter Diam α-p ß-p car myr lim 

----------------------------------------percent

3

--------------------------------- in. ----------------------number---------------------

AS-3139 18 0 1 0 22 59 1 0 25 1 0 0 0 2 

AS-3178 3 0 1 55 18 19 * 2 15 0 0 2 0 1 

AS-3187 9 * 23 23 14 29 1 2 15 0 1 1 0 1 

AS-3194 7 0 6 33 13 39 * 2 14 0 0 1 0 1 

AS-5789 23 * 10 0 29 37 * 0 14 1 0 0 1 2 

AS-A78 22 0 3 0 18 57 0 0 6 1 0 0 0 2 

AS-A95 19 0 21 0 15 45 0 0 12 1 1 0 0 2 

AS-A295 13 * 3 32 19 32 * 1 15 1 0 1 0 1 

WP-3298 26 * * 0 16 58 0 0 18 1 0 0 0 2 

WP-3299 6 0 * 43 8 40 1 2 16 0 0 1 0 2 

WP-3312 5 0 7 34 4 48 1 1 12 0 0 2 0 2 

WP-3318 27 * 10 18 3 40 0 1 14 1 0 1 0 1 

WP-3347 4 * 17 25 3 48 1 1 18 0 1 2 0 2 

WP-3352 24 * * 0 18 57 0 0 14 1 0 0 0 2 

BL-6074 7 * 11 0 27 56 0 0 24 0 1 0 0 2 

IFG-4B63 10 * 54 0 11 23 2 0 30 0 2 0 0 1 

1

α-pinene, camphene, ß-pinene, 3-carene, myrcene, limonene, G3-phellandrene, terpinolene.

2

α-pinene, ß-pinene, 3-carene, myrcene, limonene.

3

Normalized; * = trace. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 289
Chapter 6 

Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Cumming and Righter 1948). Shoots were bagged with standard filter paper 

bags with a glassene window in early spring as soon as buds showed evidence 

of female flowers: in early- to mid-April at IFG and early- to mid-May at Adin. 

When the female conelets reached the receptive stage, each bag was given a 

shot of 1.0 cc of the designated pollen using a hypodermic syringe. The puncture 

hole made by the syringe was sealed with tape. Pollen was injected from early-

to mid-June at Adin and mid- to late-May at IFG. Because the flowers on a 

single tree do not develop at the same rate, it was often necessary to work with 

a single tree for several days, and to work with a group of trees for a week or 

two. The uncertain spring weather at both locations, particularly at Adin 

Summit, and the normal biological variation of flowering also tended to stretch 

out the development period of the female conelets. 

Pollination bags were removed, when conelet scales had been closed for 

about 3 weeks, to allow the shoot to grow freely, and an insecticide was applied 

when the bags were removed. 

Early the next spring, cloth cone bags were placed over the shoots bearing 

the control pollinated conelets, both to protect the cone and to catch seed if seed 

drop was earlier than anticipated. From much experience by IFG personnel, it 

was found that cone bags cause little or no decrease in cone or shoot 

development. It should be noted that cones of P. ponderosa require two growing 

seasons to mature. 

Cones were collected between mid-August and mid-September and were 

taken to IFG where seeds were extracted and stored at about 1 °C. Cones from 

five trees at Adin were recorded for seed production to determine the effect of 

the bagging and possible incompatibility between Adin and Wheeler trees 

which were about 400 miles apart. Seed stratification, establishment of nurseries 

and plantations, acquisition of resin samples, and GLC analysis are described 

in Chapter 5. 

Resin samples were obtained by severing or mini-tap as described in 

Chapter 5. 

GLC analyses were made of the monoterpene composition of 4- to 11-yearold progeny. Though the resin composition of these young trees may not have 

been quite that of a mature tree, the data appeared to be suitable for analysis on 

a comparative basis, and the conclusions drawn on the data were considered 

valid. Averages for compositions will be given, but it was believed that an 

analysis of the frequency distribution was much more appropriate, valid, and 

meaningful. Optical isomers were not separated. 

Generally, 25 or more samples, i.e., progeny, were needed for good 

resolution of frequency distribution, though more confident interpretation was 

made with a greater number. 

Normalized data of monoterpene composition for each set of progeny were 

first analyzed for averages and frequency distribution for each subset of age 

and place of growth. Subsets were aggregated if there was little or no difference 

due to age (and usually there was not). They were not aggregated by place of 

growth because there usually were substantial differences. On the other hand, 

the composition of 4-year-old container trees was nearly always similar to that 

of nursery-grown trees, as shown by averages and by the characteristics of the 

frequency distributions. Therefore, the data for 4-year-old container trees were 

used alone or were aggregated with the data for nursery-grown trees for 

further analysis. If place of growth caused marked difference in composition, 

only nursery-grown trees were aggregated for further analysis. Data on other 

places of growth—container, container/plantation, or plantation—were carried 

no further. (The 7- to 9-year-old container trees had a much different watering 

and culturing schedule than the 4-year-old container trees.) The aggregated 

nursery data were reanalyzed for basic statistics and frequency distributions. 

290 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smi

th Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

It is important to emphasize again that measurements at different ages of 

nursery growth were not of the same set of trees but were of other sets of trees 

that were grown from the same seed lot. 

A modal analysis (Macdonald and Green 1988) was made of all multimodal 

frequency distributions generally having 25 or more measurements. In the case 

of sets with fewer than 25, a few analyses were also made if there appeared to 

be a clear separation of modes. This analysis produced the means and 

proportions of the modes in a distribution. In several cases, modal analysis was 

not performed where the modes were very clearly separated. However, in most 

of these distributions the modes were not sharply and clearly separated. The 

number of modes derived from the analysis was compared to the number that 

was expected from the assignment of alleles to the two parent trees on the basis 

of their monoterpene composition. These data on the number of modes were 

used for genetic interpretation. Though this analysis also provided the 

proportion of the measurements in each mode, proportions were not decisive 

values for genetic interpretation but were used as corroborating evidence. Most 

sets of progeny had fewer than 50 trees, and with so many factors other than the 

basic alleles acting on a limited quantity of the C-5 precursor, it was possible 

that a shifting of just a few measurements from one mode to the other could 

make large changes in the relative proportions in the modes. Even with these 

uncertainties, many proportions were quite close to the expected. Mode 

proportions could be improved by using the expected number of modes rather 

than the number actually found in the calculation, which often produced more 

modes than expected because of the interaction of several modifying factors on 

the monoterpene system. The modal analysis also developed a chi square, and 

this was usually less than the degrees of freedom; therefore, the analyses were 

considered reasonable and the conclusions valid. When families were too small 

for modal analysis, the means and frequency distributions were given because 

they contributed to the interpretation. In several cases, when there was a clear 

separation of a mode near zero from one or more modes further along the 

percent scale, data for the mode near zero were not used in the modal 

analysis, but they were included in the modal count. This was particularly so 

for 3-carene. 

A hypothesis is proposed, with supporting evidence presented, that the 

primary and dominant structure for determining the monoterpene composition 

of P. ponderosa xylem resin is two additive alleles at a single locus for each of 

five monoterpenes: α-pinene, ß-pinene, myrcene, limonene, and 3-carene. The 

evidence that will be discussed in this section was quite strong for the stated 

hypothesis, and there was considerable supporting evidence in the studies of 

half-siblings (see Chapter 5) and in the survey of local and regional variation of 

the 19 pine species of California (see Chapter 3). There also might be one or 

more secondary and minor genetic mechanisms that can cause small shifts in 

the level of a given component; these secondary mechanisms, if they exist, have 

yet to be resolved. There were a number of factors, in addition to the basic 

genetic structure, that could also affect the amount of a major component as 

follows: age of tree (called the juvenile effect), isomerization, biosynthetic byproducts, geographic source of tree, interaction of monoterpenes, and several 

forms of stress such as prolonged container growth, over application of a phytocide, and grafting. These several factors, as well as the possibility of a 

minor genetic structure, were secondary and their effects usually quite small. 

In aggregate, however, they could appreciably lower the resolution of the 

primary structure and deviations from the expected values. Four other 

monoterpenes—camphene, ß-phellandrene, γ-terpinene, and terpinoline— 

were often present in small to trace amounts. They appeared to be products of 

isomerization or biosynthetic by-products, and were considered minor 

components. Of course, there could be a separate genetic mechanism for some of 

the minor components. These minor components were included in the 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 291 
Chapter 6 

Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

normalization, were not used in modal analysis, but were sometimes included 

in displays of frequency distributions. 

Each of the five major monoterpenes can, therefore, have one of three sets 

of additive alleles: (0-0), (0-1), or (1-1). And each tree can have one of the three 

sets for each major monoterpene. 

During the course of the work on full siblings another source of variation 

became apparent which seemed to be related to the distance between parents. 

In effect, the composition of progeny of parents which were far apart tended to 

have the characteristics of trees under some degree of stress, generally higher 

in α-pinene and ß-pinene and lower in limonene and myrcene. 

It will be shown that, within the constraints noted above, the quality and 

quantity of resin compositions of progeny were quite predictable when 

based on the additive allele assignment to the parents based on their 

resin composition. 

For each family where modal analysis was used, the following will be 

given: (a) the frequency distribution of each monoterpene, (b) the modal 

analysis of each multimodal distribution where there were adequate sample 

numbers; (c) the means and proportions of the analyzed modes, (d) the number 

of modes expected from the assignment of alleles to the parent trees and the 

number of modes found by the analysis, and (e) the types of composition which 

were found in each family. In some cases an analysis was not made for 

distributions that were clearly two or three modes. 

The results of the modal analysis were interpreted as follows. If the number 

of modes derived from the modal analysis equalled or exceeded the number 

expected from the assignment of alleles to the parent trees, the additive allele 

hypothesis was satisfied. It was presumed that modes in excess of the expected 

number were caused by the interactions between monoterpene alleles for the 

limited amount of precursor and by the action of several modifying factors 

noted above. 

The individual tree compositions in each family were classed into types 

similar to, but not fully the same as, that used for half-siblings in Chapter 5. 

Types of composition were selected which represented those in a family, in the 

families of a female, and in all the families in the study. It was not possible to 

quantify the occurrence of these types because of the wide range in family size. 

However, an estimate was made of whether each type occurred commonly or 

occurred but not commonly. 

Crosses in Chapter 6 will be discussed by the families of the seven 

female parents with subheadings of pollen sources, the male parent, for 

each separate family. 

Each parent tree was identified by a combination of numbers and letters. 

The first two letters showed the tree's location as follows: AS = Adin Summit, 

Modoc National Forest, WP = Wheeler Peak, Great Basin National Park, RP = 

Ranger Peak, Los Padres National Forest, BL = Blue Lake, Modoc National 

Forest, IFG = Institute of Forest Genetics, Placerville, Calif. (fig. 5-1). 

Throughout this chapter, as was shown in Chapter 5, the composition of 

young trees was not fully what was expected from the combinations of the 

compositions of the parent trees. This effect was called the juvenile effect; it was 

manifested by greater α-pinene and ß-pinene than expected and by lesser 

myrcene and limonene than expected. As noted earlier, this same effect was 

caused by factors associated with stress. However, though stress and the juvenile factor caused average composition values to deviate from the expected, 

the number of modes was unchanged. In effect, these modifying factors moved 

the modes up or down the percent scale depending on the mix of components. Thus 

the strong support for the additive allele hypothesis was the number of modes in the 

distribution of a component. Mode proportions gave additional support. 

292 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

Crosses of P. ponderosa AS-3139 with 10 Pollen Sources 

Tree AS-3139, the first high limonene tree that was found, was at Adin Summit 

(AS) on the Modoc National Forest (fig. 5-1, table 6-1). It was about 20 inches in 

diameter with good growth and good form. It was also successfully grafted at 

IFG, and three grafted trees are now growing in the Camino Arboretum. The 

reanalysis of Tree AS-3139, as well as the other parent trees at Adin Summit, 

showed their compositions to be essentially the same with changes in time and 

location of sample on the tree (table 6-2). This refuted the claim of others that the 

compositions of these trees were spurious measurements. The breeding studies 

reported in this chapter also showed the compositions to be valid and not spurious. 

Pollen from 10 trees was used on Tree AS-3139; two of these pollen sources 

were used on the grafts of Tree AS-3139 at IFG (table 6-3). 

The average composition of sets of full-sibling progeny between Tree AS3139 and 10 male parents was recorded (table 6-3). 

The measurements of the five trees for compatibility and for seed 

production were as follows (Trees WP-3298 and WP-3352 are at Wheeler Peak, 

about 400 miles from Tree AS-3139; Trees Adin 4 and 5 were other windpollinated trees, at Adin Summit, that were selected for only this one cone study): 

AS-3139 AS-3139 AS-3139 Adin-4 Adin-5 

x x x x x 

WP-3298 WP-3352 wind wind wind 

Cones protected yes yes no no no 

Number of cones used 10 14 12 42 13 

Number of sound seed/cone 78 69 46 45 48 

Milligrams/seed 44 47 45 40 48 

It was apparent that there was no noticeable incompatibility between the 

tree at Adin, AS-3139, and those at Wheeler, WP-3298 and WP-3352; that seed 

yield was greatly increased by protecting the first- and second-year conelets, 

and that there was no clear difference in seed weight because of parent source 

or treatment. Weight of seed was about average for P. ponderosa. 

Progeny of P. ponderosa AS-3139 x WP-3298.

Tree WP-3298 was classed as a high limonene and was growing at Wheeler 

Peak (table 6-1); its monoterpene composition was essentially the same as that

of Tree AS-3139 growing at Adin Summit, with about 58 percent limonene. 

Thus, this was a cross of two high limonene trees. 

Normalized percent compositions of parents and progeny were as follows: 

Trees and type Number α-pinene /1-pinene 3-carene myrcene limonene 

AS-3139 female 1 18 1 0 22 59 

WP-3298 male 1 26 0 0 16 58 

F-1 progeny 115 39 4 1 5 52 

Resin of eight sets of nursery-grown progeny, ranging from 4 to 11 years 

old, were analyzed for monoterpene composition along with one set each of 9-

year-old container-grown progeny, and one set of 9-year-old plantation-grown 

progeny (fig. 6-1). There were only rather small shifts, or no shifts, in the 

average of any of the individual monoterpenes in the eight age-sets of nursery 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 293 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Table 6-2—Monoterpene composition of P. ponderosa, that were used in the breeding study, at different locations of sampling, and in different 

years; all trees were growing at or near Adin Summit, except "g" which were grafts at Institute of Forest Genetics. 

Sampling Monoterpene1 

Tree Year Aspect Height α-p ß-p 3-car myr lim 

feet percent2 

AS-3139 1968 S 4 18.0 1.0 0 20.0 60.0 

1969 S 13 18.0 0.5 0 22.1 58.5 

1969 W 20 18.7 0.6 0 22.8 57.4 

1969 E 20 18.7 0.1 0 23.7 56.5 

1985 S 4 18.5 1.0 0 21.5 59.6 

1985 W 4 18.3 1.0 0 23.0 57.4 

1985 N 4 18.0 0.9 0 23.4 57.3 

AS-3139g 1989 N 1 27.4 4.1 3.9 15.8 49.0 

1989 N 8 27.3 7.7 9.2 12.8 42.0 

AS-5789 1968 S 4 22.0 9.7 0 29.2 38.1 

1985 S 4 22.9 11.5 0 28.7 36.8 

1985 E 4 22.1 10.4 0 30.2 37.2 

1985 W 4 24.3 11.4 0 28.8 35.5 

AS-3187 1968 S 4 9.0 23.0 23.0 14.0 19.0 

1985 S 4 9.7 23.3 24.6 13.3 23.7 

1985 E 4 9.6 22.6 24.7 13.0 28.2 

1985 W 4 9.7 23.3 24.5 13.6 27.5 

AS-3178 1968 S 4 3.0 1.0 55.0 18.0 19.0 

1985 S 4 3.0 0.5 48.6 23.2 21.2 

1985 W 4 3.0 0.5 49.7 21.6 21.9 

AS-A95 1968 S 4 22.0 23.0 0 10.0 45.0 

1985 S 4 18.8 21.0 0 14.8 45.4 

1985 W 4 20.2 20.5 0 13.9 45.2 

AS-A95g 1989 S 1 33.4 27.5 3.5 10.5 25.0 

1989 S 8 42.1 27.5 0 7.6 23.8 

BL-6074 1972 E 4 7.4 10.5 0 27.3 54.7 

1985 E 4 7.2 10.2 0 27.2 55.2 

1985 W 4 7.0 10.4 0 26.9 55.6 

AS-3194 1968 S 4 9.1 11.9 33.6 10.9 32.3 

1985 E 4 9.0 11.5 32.6 12.2 32.4 

1985 W 4 7.4 7.5 34.6 14.2 42.9 

1985 N 4 8.4 8.4 35.4 12.5 32.8 

1

α-pinene, ß-pinene, 3-carene, myrcene, limonene. 2

Normalized; minor components omitted. 

294 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

Table 6-3—Average monoterpene composition of progeny of Tree AS-3139 with 10 different males grown for varying periods of time 

(years) under different conditions: nur = nursery, con = container, copl = container/plantation, plan = plantation, N = number of trees. 

Monoterpene composition of progeny' 

Male Growth Age N α-p cam ß-p car my lira ß-ph terp location 

yr 

WP-3298 nur 4-11 115 

WP-3298 con 9 3 

WP-3298 copl 9 4 

WP-3298 plan 9 22 

WP-3352 nur 4-11 60 

WP-3352 con 9 3 

WP-3352 plan 9 21 

WP-3299 nur 4-11 29 

WP-3299 con 9 5 

WP-3299 copl 9 8 

AS-A953 con 4 49 

BL-6074 con 4 38 

WP-3347 nur 4-11 33 

WP-3347 con 9 8 

WP-3347 copl 9 2 

WP-3312 nur 4-11 32 

WP-3312 con 9 9 

WP-3312 copl 9 7 

AS-5789 nur 4-11 35 

AS-5789 con 9 9 

AS-5789 copl 9 7 

AS-3194 nur 4-11 27 

AS-3194 con 9 8 

AS-3194 copl 9 5 

AS-3178 nur 4-11 33 

AS-3178 con 9 4 

AS-3178 copl 9 8 

--------------------------------------------percent'-------------------------------------------------

39.4 *2 3.6 0.9 5.2 51.9 0 * 

58.7 0.2 4.8 0.9 4.1 31.3 0 0 

63.7 0.1 4.3 0 5.2 26.7 0 0 

57.3 0.1 4.0 0.1 8.0 30.6 0 0 

30.7 * 2.2 0.3 6.3 60.5 0 0 

33.7 0.1 4.0 0.2 6.2 55.6 0 0 

44.5 0.1 3.7 0.1 8.1 43.5 0 0 

17.7 0.1 2.5 25.4 5.1 47.7 0 2.5 

22.1 0.1 5.0 32.1 3.8 34.8 0 2.0 

37.0 0.1 6.9 11.3 7.5 36.5 0 0.8 

25.4 0 24.3 2.0 2.4 45.4 * 0.1 

23.4 0 15.2 2.9 3.0 55.3 0 * 

8.7 0.1 30.3 28.4 3.7 26.8 0 1.7 

9.3 0.1 38.5 30.5 2.6 17.3 0.5 1.5 

8.1 0.1 29.8 17.4 5.0 37.5 0 2.2 

10.7 0.1 14.4 34.1 2.9 36.3 0 1.6 

10.0 0 12.0 43.0 2.3 27.3 0.1 3.0 

12.3 0.1 26.0 28.4 3.4 27.4 0.1 2.1 

27.0 * 15.5 0.1 10.9 46.5 0 0 

32.6 0.2 36.8 0.1 8.2 21.3 0.8 0 

41.4 0.1 28.9 5.1 8.8 19.0 0.2 0.6 

13.3 * 15.6 18.9 3.6 47.3 0 1.3 

24.5 * 10.3 25.5 2.2 35.3 0 2.0 

53.5 0.1 9.8 4.3 3.7 28.1 0 0.5 

9.3 0.1 2.9 41.7 7.6 35.9 0 2.5 

11.1 0 1.7 46.0 9.5 28.8 0 2.9 

23.4 * 2.7 40.1 11.2 19.5 0 3.0 

1

α-pinene, camphene, ß-pinene, 3-carene, myrcene, limonene, ß-phellandrene, terpinolene. 2

-Normalized, * = trace. 3

Grafts at IFG were pollen sources.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 295 
trees, ranging from 4 to 11 years

. All of these trees could be classed as ultrahigh, high, or potentially high limonene; that is, essentially lacking ß-pinene and 3-carene. The composition of container trees and of the plantation trees 

differed sharply from that of the nursery trees in α-pinene and limonene (table 

6-3). The amount of myrcene and ß-pinene was apparently too small to show 

the effect of place of growth. To repeat, each set of trees was a different set 

derived from the same seed lot with different ages or location of growth. It is 

hypothesized that stress, from either prolonged container growth or overdose 

of a phytocide, was the cause of the difference between the nursery-grown trees 

and trees grown at other locations. Thus, the analysis of the progeny of Trees 

AS-3139 x WP-3298 was confined to the aggregate of nursery trees which 

average 52 percent limonene, 39 percent α-pinene, and small amounts of other 

monoterpenes (table 6-3). 

The average amount of α-pinene was fairly constant at about 35 to 40 

percent for varying periods of nursery growth of 4 to 11 years (fig. 6-1), but the 

range of individual values was quite large, generally between 15 and 60 percent. 

This general range prevailed at all growth periods, even with small number of 

trees. The average α-pinene for trees grown in containers or plantations for 9 

years was much greater at about 57 percent (table 6-3). This large difference was 

attributed to the stress of prolonged root containment in containers and to the 

over application of a phytocide in the plantation. Though the averages were 

fairly constant over time in the nursery-grown sets of trees, and though the 

individual tree values ranged widely even in small families (fig. 6-1), the 

pattern of the frequency distributions was about the same for each age class. 

The caption for Figure 6-2 is the basic caption for the following 42 figures 

with modal analysis. 

Figure 6-2: On the left; frequency distribution of the amount of each of the noted 

monoterpenes in 4 to 1

1 year old progeny of P. ponderosa AS-3139 x WP-3298 each 

dot is measurement of one tree except where a circled number indicates each is that 

number; ▲ is average of set. On the right; modal analysis of the distribution of the noted 

monoterpenes; heavy line is best fit of the histogram; thin line is best fit of the modes; (▲) is average position of each mode; beneath it is the average (av) percent of each mode 

in full numbers and proportion (pr) of each mode base on a sum of 1.0 for all modes. 

In 

the middle; the expected (ex) and actual (ac) number of modes for the 5 major 

monoterpenes, expected was derived from assignment of alleles to parents, actual 

derived from modal analysis. Minor components not included in modal analysis. In 

using this caption, replace the two parents above with the two parents in the figure 

before you. 

The average amounts of camphene, ß-phellandrene, and terpinolene were 

near zero in all trees, and were not included in the calculation (fig. 6-2). The 

average amount of ß-pinene and 3-carene was very low, confirming the 

assignment of a (0-0) set of alleles for both components in both parents. What 

little amount there was of these five components was likely due to 

isomerization or biosynthetic by-products. The amount of ß-pinene, though 

quite low at about 4 percent, ranged more widely than the other four 

components, suggesting that ß-pinene could be the key component in the 

juvenile factor, as discussed in the introduction to this chapter. 

The average amount of myrcene increased gradually in the nursery-grown 

trees from about 4 percent at 4 years to about 8 percent at 11 years (fig. 6-1). The 

small number of samples (three) for the container-grown trees probably 

explains the lower myrcene than expected. The general increase in myrcene 

296 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

Figure 6-1—Frequency distribution of the amount of the noted 

monoterpenes in the progeny of P. 

ponderosa AS-3139 x WP-3298 for 

eight periods of growth (years) in 

the nursery (nur) and for one period of container (con) and plantation (plan) growth, as listed on the 

right; each dot is measurement of 

one tree; [▲] is average of set. 

(continued on next page) 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 297 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

298 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

Figure 6-2—See full description 

on page 296. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 299
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Figure 6-3—Fifty eight types of 

monoterpene composition, and 

their occurrence, in 42 full sibling 

families of seven female P. ponderosa analyzed and discussed in 

this chapter; ● = occurs commonly, ○ = occurs but not commonly; The seven females are listed 

horizontally across the top with 

the males listed vertically under 

them. See Table 6-2 for prefix letters of male parents. 

Table 6-4—Average monoterpene composition of three sets of nursery-grown progeny of P. ponderosa AS-3139 x 

WP-3298 grouped by the three classes of limonene: low = 0-39 pct., mid = 40-59 pct., high = 60-100 pct. N = 

number q f trees. 

Monoterpene1 

Class of 

limonene 

N α-p cam ß-p car my lim ß-ph ter 

----------------------------------------------percent

2

---------------------------------------------

low 22 58.4 * 3.9 0.2 5.1 32.4 0 * 

mid 67 38.0 * 3.8 1.1 5.4 51.6 0 * 

high 26 22.6 * 2.6 0.9 4.8 69.1 0 * 

1

α-pinene, camphene, ß-pinene, 3-carene, myrcene, limonene, ß-phellandrene, terpinolene. 2

Normalized; * = trace. 

300 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smi

th Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

suggested a juvenile phenomenon. 

The average amount of limonene in sets of nursery trees was fairly constant 

at about 50 to 60 percent, though individual measurements ranged widely from 

about 5 percent to almost 90 percent (fig. 6-2). The average for the containergrown and plantation-grown trees, however, was much lower at about 30 percent. Thus, it appears that under stress the amount of limonene decreased 

and α-pinene increased. 

The analysis of the frequency distributions showed that the number of 

modes actually derived by the analyses equalled or exceeded the number 

expected from the assignment of additive alleles to the parent trees (fig. 6-2). 

This supports the additive allele hypothesis. Mode proportions of α-pinene 

and limonene were close to the expected under the conditions of the study. The 

proportions of 27:49:24 for α-pinene were very close to the expected of 25:50:25; 

the 22:60:18 proportions for limonene were a reflection of the modes of α­

pinene. These modes and proportions support the assignment of a (0-1) set of 

alleles to α-pinene in both parents, and a (1-1) set for limonene in both parents. 

When all progeny were grouped by types of composition and were then 

categorized by relative abundance, it was readily apparent that nearly all 

progeny fell into the higher percentage classes of limonene (fig. 6-3). 

For further analysis, all 115 progeny were placed in three classes of 

limonene as follows: (a) ultra-high limonene, greater than 60 percent (fig. 6-3, 

#1,2,3), (b) high limonene, 40 to 60 percent (fig. 6-3, #6,7,9), or (c) potentially 

high limonene, less than 40 percent but essentially lacking ß-pinene and 3-

carene (fig. 6-3, #19,31, table 6-4). However, α-pinene was present and appeared 

to have a (0-1) set of alleles in both parents. Therefore, some progeny had a (1-

1) set of alleles for α-pinene; in such cases limonene will not be high. Likewise, 

some progeny had a (0-0) set of alleles for α-pinene; in such cases limonene will 

be ultra high. And the data on individual tree compositions supported this 

assumption (fig. 6-3). The modality of the distributions of limonene was also 

determined by varying allele composition of α-pinene. That is, the (0-1) set of 

alleles should produce progeny with a (0-0) set, a (0-1), or a (1-1) set of alleles 

for α-pinene with proportions of 1:2:1, respectively. Limonene was always (1-

1) in all progeny, but the amount of it depended on the set of alleles for 

α-pinene that was competing for the fixed amount of precursor. 

The results clearly showed the inverse relationship of limonene with α­

pinene for the high and low mode, and the direct relationship with the 

mid-mode (fig. 6-4). The allelic structure of ß-pinene, 3-carene, and myrcene 

was (0-0) in both parents and in all progeny. The question arises about the 

small amounts that do occur in the progeny. Three alternatives are proposed 

and there may be others: (a) isomerization from α-pinene and limonene, (b) a 

by-product of terpene synthesis, (c) a slight bit of activity by the (0-0) set of 

alleles under certain conditions, such as the juvenile state. 

Though the composition of the progeny will very likely change over long 

periods of time, it is possible that some progeny will still have limonene in 

excess of 80 percent and thus be classed as ultra-high limonene; trees with such 

a composition have not been found in natural stands. Type #1 (fig. 6-3) closely 

resembles P. torreyana (see Chapter 3). 

It was difficult to explain the average of 22 percent for the low mode of α­

pinene that presumably was controlled by a (0-0) set of alleles except as an 

effect of the juvenile factor. It might be possible to attribute some of this to 

isomerization, but not all of it. One might speculate that the (0-0) set of alleles 

had some level of activity, particularly with no competing alleles, except 

limonene, and during the juvenile period of growth. This same factor could 

account for the shifting of the percent scale much higher than could be expected 

from equal access to the C-5 precursor. However, a few trees of the ultra-high 

limonene type (fig. 6-3, #1) had very little α-pinene; this was the composition 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 301 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Figure 6-4—Frequency distribution of 

the amount of the 

AS-3139

composition was

high, high or potentially high

one tree except where 

noted monoterpenes in the progeny of P. ponderosa

 x WP-3298 when progeny

 classified as ultra 

for 

limonene; each dot is measurement of

 indicates

each is n trees; [▲] is average of set. 

302 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

that was expected with a (0-0) set of alleles for α-pinene and a (1-1) set for 

limonene in the progeny. The results suggested, therefore, that the juvenile

effect was quite variable or was dependent on some other variable factor. 

Progeny of P. ponderosa AS-3139 x WP-3352

Tree WP-3352 was another high limonene tree, also growing at Wheeler Peak

(WP). Its composition was nearly identical to that of both Tree AS-3139 and 

Tree WP-3298 (table 6-1).

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-3139 female 1 18 1 0 22 59 

WP-3352 male 1 24 0 0 18 57 

F-1 progeny 60 31 2 tr 6 61 

There was little change in the average composition of nursery trees over the 

4 to 11 years of growth. Therefore, all nursery trees were aggregated into one 

set of 60 trees for analysis. The average monoterpene composition of nurserygrown progeny was fairly similar to that of the progeny of Trees AS-3139 x 

WP-3298 (table 6-3), though α-pinene was bit lower and limonene a bit higher; 

the frequency distributions were also quite similar (fig. 6-5). The effects of a 

phytocide on plantation-grown trees and of root containment on containergrown trees were clearly evident, though the differences were not as great in 

the progeny of Trees AS-3139 x WP-3352 as they were in the progeny of Trees 

AS-3139 x WP-3298. Nevertheless, only the data on the nursery trees were 

analyzed further. 

The analysis of the frequency distributions showed that the number of 

modes actually found by the analysis equalled or exceeded the number 

expected from the assignment of alleles to the parent trees (fig. 6-5). The three 

modes for α-pinene support the assignment of a (0-1) set of alleles to both 

parents. Mode proportions were not as good as with the previous set of progeny 

With many fewer measurements, the trimodality of the distribution of αpinene and limonene was not as easily discernible as it was with the progeny of 

Trees AS-3139 x WP-3298. However, modal separations were about the same 

for both α-pinene at 28 and 38 percent and limonene at 45 and 62 percent. The 

lack of 1:2:1 proportions for the three modes could be attributed to the small 

sample size and the combined effect of several modifying factors noted above. 

The types of composition in this family were essentially the same as those 

found in the progeny of Trees AS-3139 x WP-3298 (fig. 6-3). 

Progeny of P. ponderosa AS-3139 x WP-3299

Tree WP-3299 was also located at Wheeler Peak (WP). It was near-high

limonene, but with high 3-carene. Normalized percent compositions of the

parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-3139 female 1 18 1 0 22 59 

WP-3299 male 1 6 0 43 8 40 

F-1 progeny 29 18 3 25 5 48 

The nursery-grown progeny of the cross were nearly as high in limonene 

(table 6-3), about 48 percent, as in the two previous crosses (Tree AS-3139 x WPUSDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 303 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Figure 6-5—Distribution and analyses of 

the monoterpenes in the progeny of P. ponderosa AS-3139 x WP-3352; see caption of 

figure 6-2 for explanation of the format 

below. 

304 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

3298 and x WP-3352), but α-pinene was much lower at 18 percent, supporting 

the assignment of a (0-0) set of alleles to α-pinene in Tree WP-3299. It was also 

observed that 3-carene in this family was higher at 25 percent, supporting the 

assignment of a (0-1) set of alleles for 3-carene in Tree WP-3299 (table 6-1). The 

composition of the container and container/plantation trees in this family was 

sufficiently different to exclude them from further analysis; only the nurserygrown progeny were used for modal analysis. The analysis of the frequency 

distributions showed that the number of modes actually found by the analysis 

equalled or exceeded the number expected from the assignment of alleles to the 

parents (fig. 6-6). This supports the additive allele hypothesis. Mode proportions 

were very good for 3-carene where a 50-50 ratio was expected. 

Though Tree WP-3299 had less limonene than the two previous males, it 

was still high limonene with a (1-1) set of alleles, and its progeny with Tree AS3139 clearly showed this by averages and by types of composition (fig. 6-3). In 

fact, the ultra-high type #1 (fig. 6-3) was more common in the progeny of WP3299 than it was in the progeny of WP-3298 or WP-3352. This suggested that the 

juvenile effect was not as strong with 3-carene as it was with α-pinene. 

Progeny of P. ponderosa AS-3139 x AS-A95 

Tree AS-A95 was located at Adin Summit and was classed as near-high

limonene but with ß-pinene. 

Normalized percent compositions of the parents and progeny were as 

follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-3139 female 1 18 1 0 22 59 

AS-A95 male 1 19 21 0 15 45 

F-1 progeny 49 25 24 2 2 45 

Tree AS-A95 differed from the previous near-high limonene tree, Tree WP3299, in having 0 percent 3-carene but having 21 percent ß-pinene (table 6-1). 

Thus Trees AS-A95 and WP-3299 were reversed with respect to ß-pinene and 

3-carene. The composition of AS-A95 was quite constant over time and 

sampling locations (table 6-2). Breeding was done on grafted Tree AS-3139 in 

the IFG Arboretum with pollen from grafted AS-A95 also in the Arboretum. All 

progeny were grown in 4-year containers. The average composition of 49 trees 

showed the difference between Trees WP-3299 and AS-A95 when Tree AS-3139 

was the female parent (table 6-3); the progeny of Trees AS-3139 x AS-A95 were 

higher in α-pinene and ß-pinene, but nearly lacking in 3-carene, while 3-

carene was much higher in the progeny of AS-3139 x WP-3299. Limonene was 

about the same for both families. 

The analysis of the frequency distributions showed that the number of 

modes actually found by the analyses equalled or exceeded the number 

expected from the assignment of alleles to the parent trees (fig. 6-7). Mode 

proportions were quite close to the expected ones. By combining to get two 

modes for 3-pinene, proportions were 51:49. The proportions for three modes 

for α-pinene were 29:33:38. 

Ten trees out of 49 with greater than 60 percent limonene—and actually 

greater than 80 percent—were classed as ultra-high limonene while 15 others 

with greater than 40 percent were classed as high limonene (fig. 6-3). Thus two 

near-high limonene trees, WP-3299 (the previous tree), and AS-A95 (with 

different composition) can produce progeny with ultra-high limonene when 

crossed with a tree of high limonene composition, AS-3139. Another common 

type, and one that was expected, was #26 (fig. 6-3) with a large amount of ßUSDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 305 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Figure 6-6—Distribution and analyses of the monoterpenes in the

progeny of P. ponderosa AS-3139 x WP-3299; see caption of figure 6-

2 for explanation of the format below.

306 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

Figure 6-7—Distribution and analyses of the monoterpenes in the 

progeny of P. ponderosa AS-3139 x AS-A95; see caption of figure 6-2

for explanation of the format below; **= mode near zero was not 

used in mode analysis, but was included in the mode count.

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 307
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

pinene. The near-equal amount of ß-pinene in the two modes supported the 

assignment of a (0-1) set of additive alleles for ß-pinene in Tree AS-A95; i.e., a 

(0-0) set in Tree AS-3139 and a (0-1) set in Tree AS-A95 should give equal 

numbers of (0-0) and (0-1) in the progeny. The bimodal character of the high 

mode of ß-pinene was attributed to the interaction with other alleles. 

Progeny of P. ponderosa AS-3139 x WP-3347 

Tree WP-3347, also growing at Wheeler Peak, was considered a near-high 

limonene. 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-3139 female 1 18 1 0 22 59 

WP-3347 male 1 4 17 25 3 48 

F-1 progeny 33 9 30 28 4 27 

Tree WP-3347 had modest amounts of both ß-pinene and 3-carene (table 6-

1); an assignment of a (0-1) set of alleles for both components was given on this 

basis. However, the breeding results indicated a (1-1) set for 3-carene in Tree 

WP-3347. And again these differences were reflected in the progeny of Trees 

AS-3139 x WP-3347 which averaged about 30 percent each for ß-pinene and 3-

carene; however, limonene was considerably lower at about 25 percent (table 

6-3), reflecting the competition of an additional allele. Thirty-three nurserygrown trees were used for modal analyses. 

The analysis of the frequency distributions showed that the number of 

modes actually found by the analysis equalled or exceeded the number 

expected from the assignment of alleles to the parent trees (fig. 6-8). Mode 

proportions for α-pinene were 45:55, thus quite close to the expected 50:50. 

If one considered other genetic structures, the progeny of this cross did not 

show a dominant-recessive structure at all for ß-pinene or 3-carene. If 

dominant-recessive were to prevail, one would expect one mode at 0 and one in 

the mid range of the distribution. Instead, a two-mode characteristic was 

shown for both ß-pinene and 3-carene with both modes in the mid range of the 

distribution. This result would be expected for an assignment of (0-1) set of 

alleles for ß-pinene and 3-carene (fig. 6-8). 

There were high limonene progeny but none of the ultra-high type; one 

monoterpene composition, type #18, was common; the other, type #15, was not 

common (fig. 6-3). 

The lack of a mode at or near zero for 3-carene did not support the 

assignment of a (0-1) set of alleles to Tree WP-3347, as one might be inclined to 

do on the basis of 25 percent 3-carene in the male. Thus, a (1-1) set was assigned 

here and later with females AS-5789 and AS-3187. When each of these latter 

two female was crossed with WP-3347, there was no mode at or near zero; this 

confirms the assignment of the (1-1) set of alleles to WP-3347 for 3-carene. The 

25 percent 3-carene in Tree WP-3347 must be right at the dividing point between 

one and two alleles. Also, there are three other competing alleles in WP-3347 so 

that the amount of 3-carene, even with two alleles, would be lower than usual. 

308 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

Figure 6-8—Distribution and analyses of the

monoterpenes in the progeny of P. ponderosa AS3139 x WP-3347; see caption of figure 6-2 for 

explanation of the format below. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 309
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Progeny of P. ponderosa AS-3139 x WP-3312 

Tree WP-3312, growing at Wheeler Peak, was another near-high limonene tree. 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-3139 female 1 18 1 0 22 59 

WP-331.2 male 1 5 7 34 4 48 

F-1 progeny 32 11 14 34 3 36 

Thus, Tree WP-3312 was somewhat like Tree WP-3299. Thirty-two nursery 

progeny were analyzed with the above percentages. (table 6-3) 

The analysis of the frequency distributions showed that the number of 

modes actually found by the analysis equalled or exceeded the number 

expected from the assignment of alleles to the parent trees (fig. 6-9). Mode 

proportions of α-pinene were not as close to the expected as they were for 

other sets of progeny, probably because of the three measurements greater than 

18 percent that drew the average of the higher mode to 15 percent rather than 

12 percent. 

The presence of 3-carene in all progeny confirmed a (1-1) set of alleles in the 

male parent, and the lack of or only moderate amounts of ß-pinene in all 

progeny confirms a (0-0) set of alleles for ß-pinene in the male parent. Six 

progeny had 40 percent or more limonene and were classed as high limonene 

(fig. 6-3), but different from most high limonene trees, they all also had moderate 

amounts of 3-carene, as would be expected. 

Progeny of P. ponderosa AS-3139 x AS-5 789 

Tree AS-5789 was another near-high limonene tree, 37 percent, growing near 

Adin Summit. Its composition was quite constant over time (table 6-2). 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-3139 female 1 18 1 0 22 59 

AS-5789 male 1 23 10 0 29 37 

F-1 progeny 35 27 16 0 11 47 

The 29 percent myrcene was of note because Tree AS-5789 was the only tree 

with such a large amount, and it was given a (0-1) set of alleles for myrcene. Thirtyfive nursery-grown progeny were analyzed (table 6-3). Again, the few container 

and container/plantation trees had a sharp decrease in limonene with increase in 

α-pinene and ß-pinene; these trees were not used for modal analysis. 

The analysis of the frequency distributions showed that the number of 

modes actually found by the analysis equalled or exceeded the number 

expected from the assignment of alleles to the parent trees (fig. 6-10). This 

supports the additive allele hypothesis and the assignment of alleles to the 

parent trees. Mode proportions for α-pinene were only moderately good at 

43:40:17. By combining the two higher modes of myrcene, proportions of 37:63 

were achieved. 

One tree had 73 percent limonene (fig. 6-10) and was classed as ultra-high 

310 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

Figure 6-9—Distribution and analyses of the 

monoterpenes in the progeny of P. ponderosa AS-3139 xWP-3312; see caption of figure 6-2 for explanation of the format below: 

**= mode near zero was not used in modal 

analysis, but was included in the mode count. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 311 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Figure 6-10—Distribution and analyses of

the monoterpenes in the progeny of P. ponderosa AS-3139 x AS-5789; see caption of figure 6-2 for explanation of the format below. 

312 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

(fig. 6-3). Twenty-two trees had more than 40 percent limonene and were 

classed as high limonene. The higher percentage of myrcene in the progeny of 

Trees AS-3139 x AS-5789 differed from other progeny of near-high limonene 

males, and this was reflective of the 29 percent myrcene in Tree AS-5789. Both 

the high average for myrcene and the two clearly separated modes in the 

frequency distribution supported the assignment of a (0-1) set of alleles for 

myrcene in Tree AS-5789. The use of Tree AS-5789 as a female will be covered 

later and will add support to the assignment of a (0-1) set of alleles for myrcene. 

The reciprocal cross, Trees AS-5789 x AS-3139, had somewhat the same types of 

composition, but did not have an ultra-high type of limonene which was found 

in Trees AS-3139 x AS-5789, though not commonly. The two sets of reciprocals 

will be discussed in the section describing Tree AS-5789 as the female. 

Progeny of P. ponderosa AS-3139 x AS-3194 

Tree AS-3194, also growing at Adin Summit (AS), was another near-high 

limonene tree with 33 percent 3-carene (table 6-1). Its composition was quite 

constant over time and sample locations (table 6-2). 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-3139 female 1 18 1 0 22 59 

WP-3194 male 1 7 6 33 13 39 

F-1 progeny 27 13 16 19 4 47 

Again, the effects of growing in containers and container/plantation were 

clearly evident (table 6-3) with limonene much lower and α-pinene and 3-

carene much higher in container and container/plantation than in the 

nursery-grown trees. The frequency distributions of these latter two sets of 

progeny were not used in the analysis of modes, and only nursery progeny 

were analyzed further. 

The analysis of the frequency distributions showed that the number of 

modes actually found by the analysis equalled or exceeded the number 

expected from the assignment of alleles to the parent trees (fig. 6-11). This 

supported the additive allele hypothesis and the assignment of alleles to the 

parent trees. The mode proportions were only moderately close to the expected; 

the small number of trees in the sample could be the reason. However, with the 

small numbers, the three modes each for α-pinene and ß-pinene and the two 

modes for limonene were clearly evident. Better mode proportions could be 

achieved by reducing the distribution to the expected number of modes. 

Both ultra-high and high limonene trees were common in this cross between 

trees growing near each other (fig. 6-3); and the numbers of ultra-high and high 

limonene trees were much greater than when Tree AS-3139 was crossed with 

similar males which were a great distance away, such as Trees WP-3299, WP3312, and WP-3347. This again suggested that progeny of parents separated by 

great distances may be under some level of stress, and stress was usually 

indicated by lower limonene and myrcene and by higher α-pinene and ßpinene. Tree AS-3194 was somewhat similar to Tree WP-3299—both were 

near-high limonene with moderate 3-carene—and the frequency distributions 

of 3-carene, myrcene, and limonene were somewhat similar for the sets of 

progeny, though Tree AS-3194 was within 3 miles of Tree AS-3139, whereas 

Tree WP-3299 was more than 400 hundred miles from Tree AS-3139. 

Tree AS-3194 had excellent growth characteristics and could be a good 

candidate in other breeding studies. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 313 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Figure 6-11—Distribution and analyses of the

monoterpenes in the progeny of P. ponderosa AS3139 x AS-3194; see caption of figure 6-2 for

explanation of the format below. 

314 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

Progeny of P. ponderosa AS-3139 x AS-3178

Tree WP-3178 was selected for breeding because it did not have high or nearhigh limonene, but did have a very high 3-carene (table 6-1). Its composition

was quite constant over time (table 6-2). 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-3139 female 1 18 1 0 22 59 

AS-3178 male 1 3 1 55 18 19 

F-1 progeny 33 9 3 42 8 36 

Thirty-three progeny were analyzed (table 6-3). Though there was a decrease 

in limonene in container trees to 29 percent and in container/plantation trees to 

20 percent (table 6-3), there was little or no shift in 3-carene or ß-pinene. And 

there was an increase in α-pinene. However, only the nursery-grown progeny 

were analyzed further. 

The analysis of the frequency distributions (fig. 6-12) showed that the 

number of modes actually found by the analysis equalled or exceeded the 

number expected from the assignment of alleles to the parent trees. This 

supports the additive allele hypothesis and the assignment of alleles to the 

parent trees. Mode proportions were relatively close to the expected (fig. 6-12), 

especially if the expected number of modes was used. 

There were no ultra-high limonene progeny (fig. 6-3). All progeny were 

high in 3-carene—supporting the assignment of a (1-1) set of alleles for 3-carene 

to Tree AS-3178; yet nine of them could be classed as high limonene by having 

more than 40 percent. Such trees, with an aggregate sum of about 80 percent for 

limonene plus 3-carene, would be excellent candidates for bioassay with 

western pine beetle because 3-carene is the second-most toxic monoterpene to 

the beetle. 

Progeny of P. ponderosa AS-3139 x BL-6074 

Tree BL-6074 was classed as a high limonene tree, 57 percent, on the strength of 

breeding studies. It was growing near Blue Lake (BL) in the South Warners of 

the Modoc National Forest, and was probably greater than 100 years old. Its

composition was quite constant over time (table 6-2). 

Normalized percent compositions of parents and progeny were as follows:

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-3139 female 1 18 1 0 22 59 

BL-6074 male 1 7 11 0 27 57 

F-1 progeny 38 23 15 3 3 55 

Different from the other three high limonene trees (AS-3139, WP-3298, WP3352), BL-6074 had a small amount of α-pinene and moderate ß-pinene, but a 

large amount of myrcene (table 6-1). Progeny were grown only in 4-year 

containers (table 6-3). 

The analysis of the frequency distributions showed that the number of 

modes actually found in the analysis equalled or exceeded the number expected 

from the assignment of alleles to the parents (fig. 6-13). This supports the 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 315 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Figure 6-12—Distribution and analyses of the

monoterpenes in the progeny of P. ponderosa AS-3139 x 

AS-3178; see caption of figure 6-2 for explanation of the

format below.

316 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

Figure 6-13—Distribution and analyses of the 

monoterpenes in the progeny of P. ponderosa AS-3139 

x BL-6074; see caption of figure 6-2 for explanation of 

the format below; **= mode between zero and seven 

percent was not used in modal analysis, but was 

included in the mode count. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 317 
Chapter 6 

Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

additive allele hypothesis and the assignment of alleles to the parent trees. 

Mode proportions were relatively close to the expected when the effect of the 

modifying factors was considered. If the three modes for ß-pinene were 

reduced to the expected two modes, the resulting two modes would have 

proportions of 55:45. Of the 38 progeny, 17 were ultra-high limonene, greater 

than 60 percent, and 14 others were high limonene, greater than 40 percent (fig. 

6-3). Thus, there was a greater percentage of ultra-high limonene trees in this 

family than in any other family of Tree AS-3139. Though Tree BL-6074 did not 

qualify as high limonene because of the presence of ß-pinene, it does qualify 

because of the large number of ultra-high limonene progeny it produced when 

crossed with Tree AS-3139. 

Thus, BL6074 was really high limonene, and therefore was assigned a (1-1) 

set of alleles for limonene, but it was of a different kind of high limonene. It 

would have been of much value to have used Tree BL6074 as a female parent 

with several high and near-high limonene males. The nearness of Tree BL6074 

to Tree AS-3139, like Trees ASA95 and AS-3194, apparently increased the level 

of limonene and myrcene, and decreased the level of α-pinene and ß-pinene, 

thus increasing the number of high and ultra-high limonene progeny. The 

lower level of myrcene in this set of progeny than in the progeny of Trees AS-

3139 x AS-5789 suggested that Tree BL-6074 has a (0-0) set of alleles for myrcene, 

though myrcene is only 2 percent less than in Tree AS-5789. The high level of 

myrcene in Tree BL6074 might be due in part to old age. One might be tempted 

to assign a (0-1) set of alleles for myrcene since there was a suggestion of two 

modes in the frequency distribution, separated at about 3.2 percent, but the 

modal analysis could not separate the distribution into two modes. However, 

the small number of trees in the sample and the low average make such an 

assignment uncertain. It will be reported later in this chapter, in the discussion 

of the progeny of Trees AS-A78 x BL-6074, that two modes were found for myrcene. Thus there was mixed proof of an allele for myrcene in Tree BL-6074. 

Discussion: Full Siblings of P. ponderosa AS-3139 

There were little or no changes in composition with increase in age of nursery 

growth between 4 and 11 years; therefore, the aggregate data on such trees

were suitable for analyses. However, there was a tendency for myrcene to 

increase slightly with age, but this increase was considered too small to affect

the analyses. There were marked differences between nursery trees and those 

grown in containers for prolonged periods, in a plantation or in a container/ 

plantation. The data from the latter three conditions were not used for further 

analysis. Stress was postulated as one of the causes of the differences in 

composition at different locations of growth. 

The actual number of modes in the frequency distributions, as derived by 

modal analysis, equalled or exceeded the expected number of modes, as derived 

from the assignment of additive alleles to the five major monoterpenes; this 

supported the additive allele hypothesis and the assignment to Tree AS-3139 of 

sets of alleles of (0-1), (0-0), (0-0), (0-0), and (1-1), respectively, for α-pinene, ß– 

pinene, 3-carene, myrcene, and limonene. Though mode proportions were not 

always close to the expected, they were reasonably close when all the effects of 

the modifying factors were considered. Reducing the modes to the expected 

number improved the proportions, thus adding support to the hypothesis. The 

results with Tree AS-3139 also confirm the assignment of alleles to the male 

parents. 

Tree AS-3139 produced ultra-high and high limonene progeny when 

crossed with high limonene and near-high limonene males, but the number of 

these types of composition was greater with nearby males than with distant 

males. Likewise, the average limonene and the averages of the modes of the 

318 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

frequency distribution were higher with nearby males. This lower limonene in 

the progeny with distant males is much like that which occurs with forms of 

stress. Therefore, it is postulated that progeny of parents, which are far apart, 

grew under some degree of stress. 

One pollen source, Tree AS-5789, was assigned a (0-1) set of alleles for 

myrcene, and the amount of myrcene in progeny and the location of the modes in 

the frequency distribution substantiated this assignment. AS-5789 was the only 

one used in the whole population studies of P. ponderosa with an allele for myrcene. 

In all other crosses myrcene was probably derived from a nongene source. 

The results of the crosses with near-high limonene males were particularly 

encouraging in the number of ultra-high and high limonene progeny, because 

near-high limonene trees were much more abundant for breeding than high 

limonene trees. Reciprocal crosses with Trees AS-A95 and BL-6074 would have 

been very helpful. 

Data on the frequency distribution of the five major monoterpenes were 

brought together so that each could be viewed with the same base line for all 

families (fig. 6-14). Comparative frequency distributions of the individual 

monoterpenes of all 10 sets of progeny clearly showed that the position of the 

modes can shift depending on the types and number of the other alleles and on 

presence of forms of stress (fig. 6-14). However, the number of modes was fixed 

by the basic structure of the aggregate system. In some cases, the modes have 

been compressed because of the change in the scale of the base line. 

Tree AS-3139 at Adin Summit, its grafts at IFG, and many of its progeny at 

IFG could be used for further study. Likewise, Trees AS-A95, BL-6074, AS-A78, 

and AS-3194 would be good subjects for breeding studies. 

Crosses of P. ponderosa AS-A78 with Five Pollen Sources 

Tree AS-A78, another high limonene tree (table 6-1), was growing near Tree AS3139; it was found when the original stand at Adin Summit was expanded from 

80 to 390 trees. It was used and sacrificed in a subsequent resistance bioassay 

field test with western pine beetle (Smith 1982b). However, six successful grafts 

of this tree are now growing in the IFG Arboretum near Placerville; all breeding 

was done on these grafts. All progeny were grown in a 7- to 9-year-old nursery 

or in 4-year containers. Chapter 7 contains data on the monoterpene 

composition of the grafts. Different from Tree AS-3139, AS-A78 was a small 

tree, only 7 inches in diameter, growing in a small group of pole-size trees. By 

its monoterpene composition, one would suspect that one of its parents was 

Tree AS-3139, a much older tree, or it might have derived from selfing of Tree 

AS-3139. Five pollen sources were used with Tree AS-A78, and the average 

composition of the progeny was obtained for six sets, two sets for Tree WP-3298 

(table 6-5). 

Progeny of P. ponderosa AS-A78 x AS-3139 

Tree AS-3139 was also high in limonene and was the female parent in the 

previous set of progeny (table 6-1). 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-A78 female 1 22 3 0 18 57 

AS-3139 male 1 18 1 0 22 59 

F-1 progeny 61 31 4 5 60 

Sixty-one nursery-grown progeny were examined, all essentially lacked ßpinene and 3-carene, as expected, and nearly all were classed as ultra-high or 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 319 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Table 6-5—Average monoterpene composition of the progeny of P. ponderosa AS-A78 with five males. N = number of trees. 

Monoterpene composition of progeny1 

Male Place of 

growth 

Age N α-p cam ß-p car myr lim ß-ph ter 

yrs percent

2 

AS-3139 Nursery 7-9 61 31.2 * 3.9 0.1 4.5 60.3 0 * 

WP-3298 Nursery 7-9 10 63.2 0 2.4 * 4.1 30.4 0 0 

WP-3298 Container 4 4 52.1 0 10.9 0.3 3.1 33.7 0 0 

AS-A95 Container 4 29 32.5 0 28.9 2.3 2.0 34.1 0 0.1 

BL-6074 Container 4 25 26.0 0 29.4 1.3 3.0 40.1 0 0.2 

AS-3187 Container 4 18 24.3 0 34.8 20.3 2.3 17.2 0.1 1.1 

1

α-pinene, camphene, ß-pinene, 3-carene, myrcene, limonene, ß-phellandrene, terpinolene. 2

Normalized; * = trace. 

Figure 6-14—Comparative frequency 

distribution of the five major monoterpenes in the progeny of P. ponderosa AS3139 when crossed with 10 different 

males listed on the right; each dot is 

measurement of

. 

one tree, except where 

indicates each is n trees; [▲] is average of set. 

(continues on next 3 pages) 

320 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
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Siblings of P. ponderosa 

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Siblings of P. ponderosa 

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Siblings of P. ponderosa 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 323
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

high limonene with the complementary amount occurring as α-pinene (table 6-

5). One would have expected all progeny to be at least high in limonene, but as 

noted earlier with other such crosses, such as Trees AS-3139 x WP-3298, some 

progeny had only moderate limonene with a complement of high α-pinene. A 

(0-1) set of alleles for α-pinene in both parents would explain this presence of 

low, moderate, or high α-pinene; this, coupled with a (1-1) set of alleles for 

limonene in both parents and competition for a fixed amount of precursor, would 

explain the presence of moderate, high, and ultra-high limonene. 

The analysis of the frequency distributions showed that the number of 

modes actually found by the analysis equalled or exceeded the number 

expected from the assignment of alleles to the parents (fig. 6-15). This supports 

the additive allele hypothesis and the assignment of alleles to the parent trees. 

The trimodality of α-pinene and limonene was clearly evident and was strong 

evidence for additive alleles. Mode proportions for α-pinene were reasonably 

close to the expected when the effects of the modifying factors were considered, 

as noted previously. Proportions of 25:50:25 for α-pinene were expected; 

31:38:31 were achieved by the analysis. 

Three trees had greater than 80 percent limonene (fig. 6-3), and nearly 90 

percent, suggesting that near-pure limonene P. ponderosa might be produced by 

breeding, though no such trees have been found in natural stands. The types of 

composition were much like those of the progeny of Trees AS-3139 x WP-3298 

and AS-3139 x WP-3352; all three parents were classed as high limonene. Each 

of the three averages of the modes for limonene, at 36 percent, 60 percent, and 

74 percent, were higher in the progeny of Trees AS-A78 x AS-3139 than in those 

of AS-3139 x WP-3298, at 32 percent, 52 percent, 68 percent. This is pointed out to 

illustrate the postulated effect of distance between parents; Trees AS-A78 and 

AS-3139 were in close proximity whereas Tree WP-3298 was about 400 miles 

away. Also, the general characteristics of the frequency distributions of the 

progeny of Trees AS-3139 x WP-3298 and AS-A78 x AS-3139 were quite similar, 

with the modes simply occupying different positions along the percent baseline. 

Progeny of P. ponderosa AS-A78 x WP-3298

This is another cross of two high limonene trees. However, Tree WP-3298 was 

growing at Wheeler Peak, whereas Tree AS-3139, the previous male used with 

Tree AS-A78, was growing at Adin Summit. 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-A78 female 1 22 3 0 18 57 

WP-3298 male 1 26 0 0 16 59 

F-1 progeny 14 63 2 4 30 

Quite different from the progeny of Trees AS-A78 x WP-3139, the progeny

of Trees AS-A78 x AS-3298 were generally high α-pinene with limonene in 

complementary amounts (table 6-5). Nursery and container data were 

aggregated. Though a 14-tree sample was probably too small for a confident 

statement, the lack of more high limonene trees in the progeny of this cross 

suggested that the effect of distance between parents was quite pronounced. I 

suspect that with aging, the composition will shift toward greater limonene, 

because 3-carene and ß-pinene are lacking or nearly lacking in all progeny

(table 6-5). There was the possibility that the progeny of Trees AS-A78 x WP3298 were under stress because their composition does resemble 

container-grown plants. Nevertheless, two of the progeny had greater than 60 

percent limonene, and one had nearly 80 percent (fig. 6-16). Alternative 

explanations for the lower-than-expected limonene in this family were the 

324 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

Figure 6-15—Distribution and analyses of the

monoterpenes in the progeny of P. ponderosa AS-A78 x AS-3139; see caption of figure

6-2 for explanation of the format below. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 325
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Figure 6-16—Frequency distribution 

of the amount of the noted monoterpenes in the 4- to 9-year-old progeny 

of P. ponderosa AS-A78 x WP-3298; each 

dot is measurement of one tree; [▲] is 

average of set. 

326 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

juvenile effect, the distance between parents, or there were minor genetic 

differences between the two pollen sources. Trees AS-3139 and WP-3298 were 

in different ecological zones for resin. There were only four container-grown 

trees, and these resemble the nursery-grown ones, but the sample was too 

small for comment. The 14-tree sample was too small for modal analysis (fig. 6-

16); however even these few trees had a wide range in α-pinene, from about 20 

percent to 80 percent, and limonene, from 0 percent to 80 percent. 

Progeny of P. ponderosa of AS-A78 x AS-A95 

Tree AS-A95 was growing at Adin Summit and within 0.10 mile of Tree AS-A78, 

but all the breeding was done on grafts in the Camino Arboretum near Placerville. 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-A78 female 1 22 3 0 18 57 

AS-A95 male 1 19 21 0 15 45 

F-1 progeny 29 33 29 2 3 34 

Tree AS-A95 was near-high limonene, 45 percent, but it does have 21 

percent ß-pinene. Twenty-nine 4-year-old container-grown progeny were 

examined, and they reflected the composition of both parents, as expected 

(table 6-5). The amount of α-pinene was quite variable from about 12 percent to 

near 75 percent (fig. 6-17), and the amount of limonene ranged about as widely, 

from 10 to 73 percent. As with some other crosses of two trees without 3-carene, 

there were small amounts of 3-carene in some progeny, ranging from 1 percent 

to about 10 percent. One might speculate on isomerization or low activity by 

the (0-0) set of alleles as the cause of the low amount of 3-carene. 

The analysis of the frequency distributions showed that the number of 

modes found by the analysis equalled or exceeded the number expected from 

the assignment of alleles to the parents (fig. 6-17). This supports the additive 

allele hypothesis. The trimodality of α-pinene reflected the (0-1) set of alleles in 

each parent. Because both parents had a (1-1) set of alleles for limonene, the 

multimodal distribution of limonene was caused by the interaction of the three 

different sets of alleles for α-pinene, (0-0), (0-1), (1-1). Mode proportions were 

reasonably close to the expected when all the factors were considered. Mode 

proportions for α-pinene were 43:33:24; the two expected modes for ß-pinene 

had proportions of 47:53. 

There were both ultra-high and high limonene trees, as expected (fig. 6-3). 

The abundance of these types and the high average of limonene reflected the 

closeness of the parents. 

Progeny of P. ponderosa AS-A78 x BL-6074 

Tree BL-6074 was located near Blue Lake in the South Warners. It was found 

late in the work and was not used as much as other trees. Tree BL-6074 was 

classed as high limonene, but it was different from other trees of this class, in 

that it had a low amount of α-pinene and ß-pinene. 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-A78 female 1 22 3 0 18 57 

BL-6074 male 1 7 11 0 27 57 

F-1 progeny 25 26 29 1 3 40 

The progeny of Trees AS-A78 x BL-6074 and those of Trees AS-A78 x AS-A95 

were much alike in average composition and in frequency distributions (table 6-5,

figs. 6-17 and 6-18). 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 327 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Figure 6-I7—Distribution and analyses of the monoterpenes in the progeny of P. ponderosa AS-A78 x AS-A95; see 

caption of figure 6-2 for explanation of the format below; 

**= mode between zero and 12 percent was not used in 

modal analysis, but was included in the mode count. 

328 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

The analysis of the frequency distribution showed that the number of 

modes actually found by the analysis equalled or exceeded the number 

expected from the assignment of alleles to the parents (fig. 6-18). This supported

the additive allele hypothesis and the assignment of alleles to the parent trees. 

Mode proportions were only moderately close to the expected, probably

because of the excess number of modes. Myrcene appeared to have two modes, 

suggesting a (0-1) set of alleles for BL-6074. However, the general level of 

myrcene was so low that this assignment could be questioned. This was also 

noted for the progeny of Trees AS-3139 x BL-6074. The work on Tree BL-6074 

was insufficient for making a confident assessment of the structure of its alleles 

for myrcene, and the (0-0) assignment was conditionally retained. The (0-1)

assignment of alleles to ß-pinene was shown by the two clearly separated 

modes with about equal proportions. 

Both ultra-high and high limonene types of composition were found (Fig. 6-

3); ultra-high types were not common; high types were common. Both the 

general level of limonene and the abundance of ultra and high types supported 

the classification of BL-6074 as a high limonene tree and the assignment of a (1-1)

set of alleles. 

AS-A78 x AS-3187 

Tree AS-3187 was near Adin Summit. It was also heavily used as a female 

parent. Normalized percent compositions of parents and progeny were as 

follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-A78 female 1 22 3 0 18 57 

AS-3187 male 1 9 23 23 14 29 

F-1 progeny 18 24 35 20 2 17 

Tree AS-3187 was the only one used with Tree AS-A78 that had an assigned 

allele for 3-carene, and about one-half the progeny had 3-carene. Its composition 

was quite constant with time and location of sampling (table 6-2). And with 

additive alleles, two modes of equal proportions would be expected (fig. 6-19).

Modal analysis was made, though there were only 18 trees in the set (table 6-5).

The analysis of the frequency distributions (fig. 6-19) showed that the 

number of modes found by the analysis equalled or exceeded the number 

expected from the assignment of alleles to the parents. There were two modes 

for 3-carene, as expected, and the proportions of 56: 44 were very close to the 

expected. By combining to get the expected two modes for α-pinene, 

proportions were 47:53; combining to get the expected two modes for limonene 

achieved mode proportions of 39:63. 

Though a few high limonene trees were expected, none was found (fig. 6-3).

With both α-pinene and ß-pinene present in Tree AS-3187, the juvenile effect must 

have had added strength, thus lowering the amount of limonene more than usual. 

There were no potential high limonene trees. Whenever 3-carene or ß-pinene was 

low or lacking, the composition went to α-pinene and not to limonene. 

Discussion: Full Siblings of Tree AS-A78 

In all cases, the actual number of modes in the frequency distribution of the 

individual monoterpenes, derived by modal analysis, equalled or exceeded the 

expected number of modes, as derived from the assignment of alleles to the 

parents. This supported the additive allele hypothesis and the assignment of 

alleles to Tree AS-A78 and the male parents. Mode proportions were reasonably

close to the expected under the conditions of several modifying factors; this

was additional support for the hypothesis. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 329 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Figure 6-18—Distribution and analyses of the monoterpenes in the 

progeny of P. ponderosa AS-A78 x BL-6074; see caption of figure 6-2 for 

explanation of the format below. 

330 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

Figure 6-19—Distribution and analyses of the monoterpenes in the 

progeny of P. ponderosa AS-A78 x AS-3187; see caption of figure 6-2 for 

explanation of the format below. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 331
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Tree AS-A78 produced ultra-high and high limonene progeny when crossed 

with high limonene males. However, the incidence of such trees was greater with 

nearby males than distant males. This is further evidence that there is some level of 

stress in the progeny of parents that are separated by great distances. 

The number of modes in a frequency distribution was primarily fixed by 

the alleles of the parent trees, but where these modes were located along the 

percent scale was affected by the other alleles and by a number of other factors 

such as age, stress, and possibly by a minor genetic structure (fig. 6-20). 

Several grafts of Tree AS-A78 are available for further research at IFG. 

Crosses of P. ponderosa AS-A95 X Six Pollen Sources

Tree AS-A95 was classed as high limonene, 45 percent (table 6-1) with no 3-

carene and moderate amounts of α-pinene (19 percent) and myrcene (15

percent); however, it had moderate ß-pinene (21 percent), whereas other high 

limonene trees had little or no ß-pinene. Its composition was essentially 

constant over time and with sample location (table 6-2). Tree AS-A95 was 12 

inches in diameter and growing at Adin Summit, and it had excellent form and 

growth. However, the breeding was done on two grafts growing in the Camino

Arboretum near Placerville. Composition of the graft was given in Chapter 7. 

Pollen of six trees was used (table 6-6).

Progeny of P. ponderosa AS-A95 x AS-3139 

This was a cross of two high limonene trees; the natural trees were growing 

within 100 meters of each other. 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-A95 female 1 19 21 0 15 45 

AS-3139 male 1 18 1 0 22 59 

F-1 progeny 26 20 14 * 5 60 

Tree AS-A95 was classed as a high limonene tree though it had only 45 

percent limonene rather than 60 percent; this was caused by the presence of 21 

percent ß-pinene, giving ß-pinene an assignment of (0-1) set of alleles. The 

breeding showed that it did have a (1-1) set of alleles for limonene and a (0-1) 

set for ß-pinene. The average percent composition of 26 nursery-grown 

progeny for limonene was 60 percent, one of highest of all the sets of progeny 

(table 6-6). Container trees were much lower in limonene, much higher in ßpinene, and moderately higher in α-pinene (table 6-6, fig. 6-21). Therefore, only 

the data on the nursery sets were analyzed further. The two sets of reciprocal 

crosses—AS-3139 x AS-A95 and AS-A95 x AS-3139, which were discussed under 

AS-3139 as female—had similar compositions, respectively, for the five major 

monoterpenes: for the progeny of Trees AS-A95 x AS-3139 it was 20:14:0:5:59, and 

for the progeny of Trees AS-3139 x AS-A95 it was 25:24:2:2:45. The characteristics of 

the frequency distributions were quite similar also (figs. 6-7 and 6-22). 

The analysis of the frequency distributions showed that the number of 

modes actually found by the analysis equalled or exceeded the number 

expected from the assignment of alleles to the parent trees (fig. 6-22). Mode 

proportions were not as close to the expected as was found in most other 

families. This could have been caused by the action of the modifying factors or 

the small size of the sample. However, the proportions of 58:42 for ß-pinene 

were quite close to the expected 50:50. The three modes for α-pinene at 56:26:18 

were not too good, probably because of the small size of the sample and the 

several modifying factors. 

332 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

Table 6-6—Average monoterpene composition of the progeny of P. ponderosa AS-A95 with six males when grown in three locations. N = 

number of trees. 

Monoterpene composition of progeny2 

Male 

parent 

Growth1 

place 

Age N α-p cam ß-p car myr lim ß-ph ter 

yr percent3 

AS-3139 nur 6-7 26 20.4 * 14.2 0.3 5.2 

AS-3139 con 9 8 26.8 0.1 31.5 0.9 2.4 

AS-3139 copl 9 4 12.5 * 39.6 22.0 4.5 

WP-3298 nur 6-7 34 40.5 0.1 27.6 0.2 4.7 

WP-3298 con 9 7 46.6 0.2 35.9 0.9 2.3 

WP-3298 copl 9 4 52.3 0.1 12.4 0 5.9 

WP-3352 nur 6-7 9 33.6 0.1 28.0 0.3 4.1 

WP-3352 con 9 7 32.9 0.1 34.9 2.6 2.0 

WP-3352 copl 9 8 47.4 0.1 23.0 0.2 3.3 

AS-3194 nur 6-7 27 13.4 0.1 24.0 22.9 2.0 

AS-3194 con 9 5 17.2 0.1 27.5 18.9 2.1 

AS-3194 copl 9 4 46.1 0 23.8 9.1 2.7 

AS-5789 nur 6-7 33 36.8 0.1 27.7 0 7.7 

AS-5789 con 9 8 37.8 0.2 38.0 1.0 5.3 

AS-5789 con 9 8 28.4 * 51.7 1.0 2.8 

AS-5789 copl 9 9 50.9 0.1 34.9 0 4.7 

BL-6074 con 4 7 21.4 * 42.1 2.9 2.4 

59.8 0 0 

38.3 0 0.1 

20.4 0 1.0 

26.9 0 * 

13.3 0.7 * 

29.3 0 0 

33.1 0 0 

27.0 0.3 0.2 

25.9 0 0 

35.7 * 1.6 

32.8 0 1.4 

17.0 0 1.1 

27.7 0 0 

17.2 0.4 0.1 

15.3 0.8 0.1 

8.8 0.5 0 

30.1 0.8 0 

1

nur = nursery; con = container; copl = container-plantation. 2

α-pinene, camphene, ß-pinene, 3-carene, myrcene, limonene, ß-phellandrene, terpinolene. 3

Normalized; * = trace. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 333 
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Siblings of P. ponderosa 

Figure 6-20—Comparative frequency distribution of the amount of the 

four noted monoterpenes of the progeny of P. ponderosa AS-A78 when 

crossed with five different pollen 

sources in a nursery (nur) or container (con), listed on the right; progeny 

of Trees AS-A78 x WP-3298 grown in 

both nursery and container;, each dot 

is measurement of one tree; [▲] is 

average of set. 

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Siblings of P. ponderosa 

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Siblings of P. ponderosa 

Figure 6-21—Comparative frequency distribution of the five major monoterpenes in the 

progeny of P. ponderosa AS-A95 x AS-3139 at 

three places of growth listed on the right: 

nursery (nur), container (con), container/plantree; [▲] is average of set. 

tation (copl); each dot is measurement of one 

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Siblings of P. ponderosa 

Ultra-high limonene progeny were common (fig. 6-3). Thus, as noted, earlier 

Tree AS-A95 performed like a high limonene tree. The closeness of the parents, 

about 100 yards, might also be a factor in the higher amount of limonene. 

The frequency distribution of limonene in nursery-grown trees was of 

particular note in that it had such a strong mode between 70 and 80 percent (fig. 

622). This was the strongest mode achieved in a cross of two high limonene 

trees. 

Types of composition for the two reciprocal crosses were similar (fig. 6-3): 

types 1, 3,6 for Tree AS-3139 x AS-A95 and types 2 and 8 for Trees AS-A95 x 3139. 

Progeny of P. ponderosa AS-A95 x WP-3298 

This was another cross of two high limonene trees; however, Tree WP-3298 

was growing at Wheeler Peak, nearly 400 miles to the east in a different resin 

ecotype region of P. ponderosa (table 6-1). 

Normalized percent composition of parents and progeny was as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-A95 female 1 19 21 0 15 45 

WP-3928 male 1 26 * 0 16 58 

F-1 progeny 34 41 28 * 5 27 

The composition of container and container-plantation trees differed from 

nursery trees (table 6-6). Container trees had greater α-pinene and ß-pinene 

and considerably less limonene; container/plantation trees were also much 

higher in α-pinene but were much lower in ß-pinene and slightly higher in 

limonene, but the four container/plantation trees may not have been sufficient 

for a conclusion. However, only nursery data were analyzed further. 

The analysis of the frequency distributions showed that the number of 

modes actually found by the analysis equalled or exceeded the number 

expected from the assignment of alleles to the parent trees (fig. 6-23). Mode 

proportions were moderately close to the expected when the modifying factors 

were considered, though the proportions of 45:35:20 for the three modes of αpinene, and 62:38 for two modes of ß-pinene were fairly good. 

Like the previous set of progeny, the frequency distribution of individual 

components had multimodal distribution for α-pinene, ß-pinene, myrcene, 

and limonene (fig. 6-23); this was attributed to an 0-1 set of alleles for α-pinene 

in both trees, i.e., the same conditions noted for Trees AS-A95 x AS-3139. 

There were many fewer high limonene trees and no ultra-high ones (fig. 6-

3), probably because of the effect of the factor of distance between the parents. 

Progeny of P. ponderosa AS-A95 x WP-3352 

This cross, like the previous one, was another cross of two high limonene trees 

separated by about 400 miles (table 6-1). However, because there were only 

nine nursery trees, interpretation was limited. 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-A95 female 1 19 21 0 15 45 

WP-3352 male 1 24 * * 18 57 

F-1 progeny 9 34 28 * 4 33 

The average composition of nursery, container, and container/plantation 

trees was somewhat similar to those progeny of Trees AS-A95 x WP-3298 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 337 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Figure 6-22—Distribution and analyses of the 

monoterpenes in the progeny of P. ponderosa AS-A95 x 

AS-3139; see caption of figure 6-2 for explanation of the 

format below. 

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Siblings of P. ponderosa 

Figure 6-23—Distribution and analyses of the monoterpenes in 

the progeny of P. ponderosa AS-A95 x WP-3298; see caption of figure 6-2 for explanation of the format below. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 339
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

grown in the same conditions (table 6-6). Thus, the progeny of both sets, Trees 

AS-A95 x WP-3352 and AS-A95 x WP-3298, showed the strong effect of the 

distance between parents. This was not the case for the progeny of Trees ASA95 x AS-3139, where the two parents were near to each other. Though based 

on only nine trees, the frequency distributions showed considerable range in 

α-pinene, ß-pinene, and limonene (fig. 6-24). No modal analyses were made of 

the distributions. 

Though there were only nine trees, two of them were ultra-high limonene— 

clearly evident on the frequency distribution (fig. 6-24). This was unusual 

because there was only one such value in the progeny of Trees AS-A95 x WP3298, a much larger family. Tree WP-3298 was growing in the same locality as 

Tree WP-3352. Thus, the factor of the distance between parent trees has more to 

it than has been proposed. It could easily be that the aggregate of factors such 

as stress, juvenile effect, etc., could either accentuate or dampen the effect of the 

distance between parents. Or, the occurrence of the two ultra-high limonene 

trees in the progeny of Trees AS-A95 x WP-3352 could simply be an expression 

of the large natural variation that was found throughout the breeding study. 

Progeny of P. ponderosa AS-A95 x AS-3194 

Tree AS-3194 was a 12-inch-diameter tree growing near Adin Summit with

good growth and form. It was classed as near-high limonene. 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-A95 female 1 19 21 0 15 45 

AS-3194 male 1 7 6 33 13 39 

F-1 progeny 27 13 24 23 2 36 

Thus, this was a cross of a high limonene tree and a near-high limonene 

tree, growing near each other, with differing amounts of α-pinene, ß-pinene, 

and 3-carene (table 6-6). The few container and container/plantation trees were 

not included in subsequent analyses. 

The analysis of the frequency distributions showed that the number of 

modes actually found by the analysis equalled or exceeded the number 

expected from the assignment of alleles to the parents (fig. 6-25). Mode 

proportions were not very close to the expected. The proportions for α-pinene 

were apparently skewed by the one unusual measurement of more than 60 

percent. Without this one measurement, the proportions were quite close to 

50:50. By combining modes to get the expected two, proportions for ß-pinene 

were 40:60. The zero mode for myrcene is quite unusual because there is almost 

always a measurable amount of it in all trees. 

Both ultra-high and high limonene progeny were produced by these nearby 

parents, both near-high limonene (fig. 6-3). This could be a real advantage in a 

breeding program because near-high trees were much more common in natural 

stands than high limonene trees. This was another case in which the proximity 

of the two parents resulted in a higher level of limonene. 

Tree AS-3194 was used as a male with five females (Trees AS-3139, AS-A95, 

AS-5789, AS-3187, IFG-4B63), and, though it was assigned a (0-1) set of alleles 

for limonene on the basis of 39 percent, there were indications that a (1-1) might 

be an equally suitable choice. There was considerable similarity in average 

limonene and in the characteristics of the frequency distributions of sets of 

progeny when Tree AS-3194 was the male. However, the limonene of the 

progeny never reached the average of progeny of crosses of two high limonene 

340 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
Smith Monoterpene Composition of Populations of 4- to 11-Year-Old Full Chapter 6 

Siblings of P. ponderosa 

Figure 6-24—Frequency distribution of 

the amount of the noted monoterpenes in the progeny of P. ponderosa ASA95 x WP-3352; each dot is measurement of one tree; [▲] is average of set. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 341 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Figure 6-25—Distribution and analyses of the monoterpenes in the progeny of P. ponderosa AS-A95 x AS-3194; see 

caption of figure 6-2 for explanation of the format below. 

342 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000 
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Siblings of P. ponderosa 

parents, probably because Tree AS-3194 had an allele for 3-carene, but 

individual progeny could be classed as ultra-high limonene (fig. 6-3). Using 

Tree AS-3194 as a female would have been very helpful. 

Progeny of P. ponderosa AS-A95 x AS-5 789 

Tree AS-5789, another near-high limonene tree, differed markedly from the 

previous male tree, AS-3194, in all major components except limonene (table 6-1). 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-A95 female 1 19 21 0 15 45 

AS-5789 male 1 23 10 0 29 37 

F-1 progeny 33 37 28 0 8 27 

These differences, between Trees AS-3194 and AS-5789 as pollen source, 

were generally reflected in average composition (table 6-6) and in the frequency 

distribution of individual components (fig. 6-26). The comparative average 

compositions of the five major components for progeny of Trees AS-A95 x AS5789 vs. AS-A95 x AS-3194 were α-pinene, 37 vs. 13 percent; ß-pinene, 28 vs. 24 

percent; 3-carene, 0 vs. 23 percent; myrcene, 8 vs. 2 percent; limonene, 27 vs. 36 

percent. Container and container/plantation trees were not included in the 

analyses because their compositions were quite different from those of the 

nursery-grown trees. 

The analysis of the frequency distributions showed that the number of 

modes actually found by the analysis equalled or exceeded the number 

expected from the assignment of alleles to the parents (fig. 6-26). Mode 

proportions were fairly close to the expected. Proportions of 50:50 were 

expected for myrcene and were achieved. As in previous families with Tree AS5789 as male or female, there were two clearly separated modes for myrcene 

with about equal proportions; this supports the assignment of a (0-1) set of 

alleles. If the two low modes for ß-pinene were combined to get the expected 

two modes, the resulting proportions were 47:53. The proportions for α-pinene 

of 13:43:44 were considered moderately good in the presence of the several 

modifying factors and of the small sample. 

Again, ultra-high limonene progeny were produced by high and near-high 

limonene parents, though not commonly (fig. 6-3); high limonene trees were common. 

Progeny of P. ponderosa AS-A9S x BL-6074 

Tree BL-6074 was high in limonene with low α-pinene and ß-pinene (table 6-1). 

Normalized percent compositions of parents and progeny were as follows: 

Tree and type Number α-pinene ß-pinene 3-carene myrcene limonene 

AS-A95 female 1 19 21 0 15 45 

AS-6074 male 1 7 11 0 27 57 

F-1 progeny 7 21 42 3 2 30 

There were only seven trees in the family, and this was considered too few 

for interpretation of frequency distribution, but it was apparent that there were 

large ranges in the amounts of α-pinene, ß-pinene, 3-carene, and limonene 

(table 6-6) (fig. 6-27). 

There was one ultra-high limonene tree among the seven progeny 

(not tabled). 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-177. 2000 343 
Chapter 6 Monoterpene Composition of Populations of 4- to 11-Year-Old Full Smith 

Siblings of P. ponderosa 

Figure 6-26—Distribution and analyses of the monoterpenes 

in the progeny of P. ponderosa AS-A95 x AS-5789; see caption 

of figure 6-2 for explanation of the format below. 

344 USDA Forest Service Gen. Tech. Rep. PSW-GTR-177.2000