Scbarpf, Robert F.; Kinloch, Bohun B.; Jenkinson, James L. 1992. One seed source of 

Jeffrey pine shows resistance to dwarf mistletoe. Res. Paper PSW-RP-207. Berkeley, 

CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 

8 P. 

Four seed sources of Jeffrey pine (Pinus jefleyi) were selected for testing through 

controlled inoculation for resistance to dwarf mistletoe (Arceuthobiurn campylopodum). The 

pines were 7 years old and part of a progeny test planting established by the USDA Forest 

Service's Institute of Forest Genetics, Placewille, California. One of the seed sources 

{Foresthill) was considered from previous studies to be highly resistant. It was also found to 

be resistant in this study. Test trees were inoculatedin 1980 and 1981 with about 13,500 seeds 

of dwarf mistletoe. A high proportion of the seeds were lost before germination, but branches 

covered with bird-proof and insect-proof mesh lost significantly fewer seeds. Mean percentage infection based on remaining seeds was significantly lower on trees from the Foresthill 

seed source than any of the other sources. Similarly, mean percentage of trees infected was 

significantly lower for the Foresthill source than for the three others. Development of the 

endophytic system, as indicated by length of branch sweIling, and mistletoe shoot development were not significantly different among the seed sources. However, significantly fewer 

brooms developed on the Foresthill trees than on trees from two of the other sources. 

Retrieval Terms: resistance, Pinus jeflreyyi, Arceuthobium campylopodum, parasitic plants, 

conifer diseases 

The Authors: 

ROBERT F. SCHARPF, a supervisory research plant pathologist, is in charge of the 

Station's Forest Disease Research Unit, in Berkeley, Calif. BOHUN B. KlNLOCH and -. 

JAMES L. JENKINSON are ~u~ervisojresearch geneticist and plant physiologist, respectively, in the Forest Genetics Research Unit, in Berkeley. 

Acknowledgments: 

We thank several current and former Forest Service employees for their assistance in field 

inoculation and data collection: Gayle Dupper, Anne Delfino Mix, Bill Moyer, Peter Ono, 

Carline Trummer, Detlev Vogler, and John Wallack. We also thank Dave Azuma and Alice 

Ratcliff fortheir help in statistical analyses, and John R. Parmeter, Jr., FrankHawksworth, and 

Arthur McCain for technically reviewing the manuscript. 

Cover: Young Jeffrey pines were inoculatedin fall 1980 with seeds of westerndwarfmistletoe 

to rest for resistance (bottom). Freshlv collected seeds were olaced on branches at the base of 

a needle fascicle or a needle scale. Red paint marks the site of a seed (top). 

Publisher: 

Pacific Southwest Research Station 

P.O. Box 245, Berkeley, California 94701 

January 1992 

* U.S. G.P.O.: 1992-687-563 

In Brief. . . 

Scharpf, Robert F.; Kinloch, Bohun B.; Jenkinson, James L. 

1992. One seed source of Jeffrey pine shows resistance to 

dwarf mistletoe. Res, Paper PSW-RP-207. Berkeley, CA: 

Pacific Southwest Research Station, Forest Service, U.S. 

Department of Agriculture; 8 p. 

Retrieval Terms: resistance, Pinw jeflreyi, Arceuthobiurn 

campylopodum, parasitic plants, conifer diseases 

Four seed sources of Jeffrey pine (Pinus jeffreyi) were 

selected for testing through controlled inoculation for resistance to dwarf mistletoe (Arceuthobium campylopodum). The 

pines were 7 years old and part of a progeny test planting 

established by the USDA Forest Service's Institute of Forest 

Genetics, Placerville, California. One seed source growing 

near Foresthill, California, 3800 ft elevation (1 160 m) on the 

west slope of the northern Sierra Nevada, was considered from 

previous studies to be highly resistant. Three other less resistant sources tested were from (1) South Lake Tahoe, east side 

of the Sierra Nevada, 6400 ft (1950 m) elevation, (2) High 

Meadows, South Carson Range, east side of the Sierra Nevada, 

Alpine County, 8200 ft (2500 m) elevation, and (3) Laguna 

Mountain, east of San Diego, Cleveland National Forest, 5500 

ft (1675 m) elevation. The test plantings were near Camino, a 

few miles from the Institute of Forest Genetics. Five blocks of 

trees (10 trees per block) from each source were selected at 

random for testing, except that all 25 trees from the Laguna 

Mountain source were used. 

Branches were inoculated in 1980 and 1981 with freshly 

collected dwarf mistletoe seeds. In 1980, 9000 seeds were 

placed on branches at the base of needle fascicles on the test 

trees, and in 198 1, an additional 4500 inoculations were made. 

In 1980 most of the seeds were lost before infection could 

occur. In 1981 some of the branches were covered with bird 

proof mesh bags and some were covered with insect-proof 

mesh bags to prevent seed depredation. Seed loss from 

branches, number of trees infected, number of infections per 

tree, branch swelling, shoot production, and broom development were recorded for 5 years. 

A high proportion of the seeds were lost before germination and infection, but branches covered with bird-proof or 

insect-proof mesh lost significantly fewer seeds than uncovered branches. Percentage of trees infected was significantly 

lower on the average for the Foresthill source than for any of 

the other sources. Also, percentage infection based on the 

remaining seeds on branches was significantly lower for the 

Foresthill source than for any of the ochers. Differences in 

average percentage of trees infected and average number of 

infections per tree were not found among the other sources. 

Development of the endophytic system, as indicated by 

length of branch swelling, and the production of mistletoe 

shoots were not significantly different among the seed sources. 

However, significantly fewer brooms developed on the 

Foresthill trees than on trees from other sources. 

Results of the study show that a source of Jeffrey pine 

from near Foresthill appears to contain a higher proportion of 

trees resistant to dwarf mistletoe than do other seed sources 

tested, and that resistance is not expressed in terms of growth 

rate or shoot production of the parasite. 

At Mt. Danaher, the sources were planted in 10-tree plots 

randomly located throughout the plantation. Within a source 

plot, seedlings of the 10 families were randomly located in two 

rows of 5 trees spaced 10 feet (3.0 m) apart. For our tests, five 

10-tree plots were selected at random for each source. The trees 

in each plot were flagged and tagged for inoculation. 

At Fruitridge, several sources were randomly located in 

closely spaced row plots. In 198 1, all except the Laguna Mountain source was removed. Twenty-five of the Laguna Mountain 

trees remained, and were used for inoculation. 

For inoculations, fresh seeds of dwarf mistletoe (A. 

campylopodurn) were obtained in the fall of 1980 and 1981 from 

naturally infected Jeffrey pines in the Lake Tahoe Basin, El 

Dorado County. Seeds were collected and stored for use as 

described by Scharpf and Parmeter (1962). We inoculated test 

trees within one month of seed collection by placing moistened 

seeds on branches at inoculation sites marked by a small dab of 

red paint. An inoculation site was the portion of a branch at the 

base of a needle fascicle or at the base of a scale leaf Cfig. I). Only 

portions of branches with green tissue and undeveloped bark 

were inoculated. 

In general, only a small proportion of the initial number of 

seeds that land on hosts causes infection. Some seeds are lost 

before reaching an infection site on a branch, and some are lost 

before germination and infection can occur. The proportion of 

dwarf mistletoe seeds that remain on branches after they have 

reached the site of infection has been recorded as low in most 

instances (Roth 1959; Scharpf and Parmeter 1967b, 1982; 

Wicker 1967). Therefore, a large number of inoculations were 

made to adjust for the low proportion of seeds expected to 

remain on branches. 

In 1980, about 9,000 inoculations were made on 150 trees 

in the Mt. Danaher Twenty seeds were placed on 

each of three tagged branches selected at random on each test 

tree. An analysis of variance was used to determine significant 

differences in seed loss among the three sources tested. No 

inoculations were in the Fruitridge plantation in 1980. 

In 1981, the same 150 trees were inoculated again at Mt. 

Danaher. This time, 10 seeds were used on each of three 

different branches for a total of 4500 inoculations. One branch 

on each tree was enclosed in an "insect-proof' mesh bag, one 

was enclosed in a "bird-proof' mesh bag, and one was left 

exposed as before (jig. 2). Insect- and bird-proof bags were 

used in this test because the 1980 inoculations showed that 

heavy seed loss occurred before seeds could germinate and 

infect the host. We attributed this loss to either predation by 

insects or birds or both. 

Figure I-A moist seed of dwarf mistletoe placed on a branch at the base of a needle fascicle. 

USDA Forest Service Res. Paper PSW-RP-207. 1992. 

Tukey t-test showed that there was a significantly higher percentage of seed loss, on the average, from uncovered branches 

than from branches covered with a bird-proof or an insect-proof 

bagfig. 4). On the other hand, there was no significant difference in the average loss of seeds between branches covered by 

bird-proof bags and insect-proof bags. Both birds and insects 

were excluded from the insect-proof bags, but seed predation 

by insects was not prevented by the bird-proof bags. 

Therefore, for uncovered seeds inoculated on branches in 

both 1980 and 198 1, usually fewer than 20 percent remained on 

branches and were potentially able to germinate and infect the 

host. For seeds covered by bags, about 30 to 50 percent remained on branches. 

.'; r 6 P' . ;:Pi ,.,.I 

8 111 ::: 1

1' 1 

::j,:; 

.+ 

Infection 

: 

A Tukey t-test showed that the percentage of the trees 

infected by dwarf mistletoe differed significantly between the 

Foresthill and other sources (table I). In 1980, half of the High 

Meadows trees, 24 percent of the South Lake Tahoe trees, and 

8 percent of the Foresthill trees were infected after 5 years. In 

198 1, nearly half of the High Meadows, South Lake Tahoe, and 

Laguna Mountain trees-were infected in contrast to 20 percent 

infection of the Foresthill, trees. Therefore, in evaluating resistance to dwarf mistletoe based on the proportion of trees inTable 1-Dwarf mistletoe seed retention and infection of Jeffrey pine 

inoculated in1980 and 1981 

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Jeffrey pine Trees infected 1 seed sources1 in 1985 

Fall 1980: 

High Meadows 

South Lake Tahoe 

Foresthill 

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'Fifty trees per source were inoculated, except for 25 trees from Laguna 

Mountain. 

21noculation totaled 3000 seeds per source in 1980, and 1500 seeds per source 

in 1981, except for 720 for the Laguna Mountain source. 

Seeds on branches 

the spring after 

inoculation2 

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

50 12.7 21.8 

24 8.7 14.5 

8 6.0 4.4 

Fall 1981: 

High Meadows 

South Lake Tahoe 

Foresthill 

Laguna Mt. 

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High Mdws. S. Lake Tahoe Foresthill Laguna Mt. 

Infections in 

1985-1986 from 

seeds on branches 

46 34.6 10.0 

44 28.2 7.8 

20 26.2 3.3 

48 41.3 9.1 

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Figure 4--Insect- and bird-proof mesh bags improved retention of seeds on branches of Jeffrey pines for 

5 months after inoculation in 1981. 

USDA Forest Service Res. Paper PSW-RP-207.1992. 

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However, there was wide variation in length among infections 

even within sources and among infections on the same tree. It 

appears that root development of he parasite, as indicated by 

branch swelling, is probably influenced more by branch vigor or 

other host conditions not related to resistance. 

It is well known that dwarf mistletoe-infected branches 

that develop into witches' brooms constitute an energy sink 

that, over time, weakens a tree and reduces growth 

(Hawksworth 1961). As shown below, a fairly high proportion 

of the branch infections were stimulating broom development 

Ifis. 5): Using a binomial proportion to determine the mean 

differences in broom formation, we determined that the 

Foresthill source was producing significantly fewer broorns 

than the South Lake Tahoe and Laguna Mountain sources, but 

not fewer than the High Meadows source. 

Seed source 

High Meadows 

South Lake Tahoe 

Foresthill 

Laguna Mountain 

Mistletoe 

infections 

in 1985 

No. 

96 

42 

13 

22 

Infections 

forming brooms 

in 1985 

Pct 

26 

36 

23 

45 

Broom development did not appear restricted to certain 

trees within the sources, but occurred on several trees from 

different parents and sources. For example, the three brooms 

that occurred on the resistant, Foresthill source occurred as 

single brooms on each of three different trees from different 

parents. Similarly, the 15 brooms on the Lake Tahoe source 

occurred on trees from eight different parents. Brooms developed on trees from seven parents from the High Meadows 

source, and 9 of the 18 infected trees from the Laguna Mountain source bore infections that developed into brooms. Because broom development is a function of branch growth, it is 

possible that additional brooms will develop over time from 

existing infected branches on trees of all seed sources. It remains to be seen whether brooms increase in number or enlarge 

at the same or at different rates on trees from the different seed 

sources. 

Shoot and Fruit Development 

No marked differences were noted in the development of 

dwarf mistletoe shoots among the sources tested. At least some 

plants on some trees from all sources were showing early signs 

of shoot development within 2 years after inoculation (fig. 6). 

By the third year after inoculation, most of the young plants 

bore either developing shoots ox buds pushing through the bark 

on the swollen portion of branch tissue. Some infections remained latent within branches and did not appear until three or 

more years after inoculation, however. A major complication 

arose in attempting to follow the development of shoot and 

fruit production of the dwarf mistletoe plants. In summer 1984, 

Figure 6--Localized branch swelling and the presence of small buds of 

the parasite are the first symptoms and signs of infection by dwarf 

mistfetoe. Note that the dwarf mistletoe seed is often still present when 

symptoms appear. 

a plague of grasshoppers ate nearly all the shoots, flowers, and 

fruit on the test plants, thereby precluding any long-term study 

on shoot and fruit development (Scharpf and Koerber 1985). 

However, by 1987, some shoot regrowth had taken place, and a 

comparison could be made of growth among plants on trees 

from the different seed sources (table 3). For all seed sources, 

most plants were observed with 10 or more well-developed 

shoots. Some plants bore fewer than 10 shoots, and few were 

observed with no shoots or only buds. As a result, no marked 

differences in shoot development among seed sources were 

apparent in the years after shoot removal by grasshoppers. 

Infections on the resistant, Foresthi11 source trees appeared to 

develop as many shoots as did infections on trees from the 

other sources, and presumably will be able to produce fruit and 

reproduce equally as effectively. 

USDA Forest Service Res. Paper PSW-W-207. 1992. 

References 

Hawkswonh, Frank G. 1961. Dwarfmistletoe of ponderosa pine in the 

Southwest. Tech. Bull. 1246. Washington, DC: U.S. Department of Agriculture; 112 p. 

Hawksworth, Frank G.; Edminster, Carleton B. 1981. Carlos Bates' dwarf 

mistletoe resistant ponderosa pines: A postscript after half a century. 

Res. Note RM-412. Fort Collins, CO: Rocky Mountain Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture; 4 p. 

Hawksworth, Frank G.; Wiens, Delbert. 1972. Biology and classification of 

dwarf mistletoes (Arceuthobium). Agric. Handbook 401. Washington, 

DC: Forest Service, U.S. Department of Agriculture; 234 p. 

Roth, Lewis F. 1953. Pine dwarf mistletoe on the Pringle Falls Experimental Forest. Res. Note 91. Portland, OR: Pacific Northwest Forest and 

Range Experiment Station, Forest Service, U.S. Department of Agriculture; 3 p. 

Roth, Lewis F. 1959. Natural emplacement of dwarf mistletoe seed on 

ponderosa pine. Forest Science 5: 365-369. 

Roth, Lewis F. 1966. Foliar habit of ponderosa pine as a heritable basis for 

resistance to dwarf mistletoe. In: Gerhard, H. D., and others, eds. Breeding pest resistant trees. Oxford: Pergamon Press; 221-228. 

Roth, Lewis F. 1974a. Resistance of ponderosa pine to dwarf mistletoe. 

Silvae Genetica 23(4): 116-120. 

Roth, Lewis F. 1974b. Juvenile susceptibility of ponderosa pine to dwarf 

mistletoe. Phytopathology 64(5): 689-692. 

Scharpf, Robert F. 1962. Growth rate of the endophytic system of the dwarf 

mistletoe on Digger pine. Res. Note 193. Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture; 5 p. 

Scharpf, Robert F. 1984. Host resistance to dwarf mistletoes. In: 

Hawksworth, Frank G.; Scharpf, Robea F., tech. coords. Biology of dwarf 

mistIetoes: proceedings of the symposium; 1984 August 8, Fort Collins, 

CO. Gen. Tech. Rep. RM- 11 1. Fort Collins, CO: Rocky Mountain Forest 

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Schqf, Robea F. 1987. Resistance of Jeffrey pine to dwarf mistletoe. In: 

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Scharpf, Robert F.; Koerber, Thomas W. 1985. Destruction of shoots, flowers 

and fruit of dwarf mistletoe by grasshoppers in California. Canadian 

Journal of Forest Research 16: 166-168. 

Scharpf, Robert F.; Parmeter, J. R., Jr. 1962. The collection, storage and 

germination of seeds of a dwarfmistletoe. Journal of Forestry 

60(8): 551 -552. 

Scharpf, Robert F.; Parmeter, 5. R., Jr. 1967a. Spread of dwarfmistletoe into 

Jeffrey pine plantation-trees infected after 22 years. Res. Note PSW141. Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture; 6 p. 

Scharpf, Robert F.; Parmeter, J. R., Jr. 1967b. The biology and pathology of 

dwarfmistletoe (Arceuthobium campylopodum f. abietinum) parasitizing true firs (Abies spp.) in California. Tech. Bull. 1362. Washington, 

DC: Forest Service, U.S. Department of Agriculture; 42 p. 

Schqf, Robert F.; Parmeter, J. R., Jr. 1982. Population dynamics of dwarf 

mistletoe on young true firs in the central Sierra Nevada, California. 

Res. Paper PSW-161. Berkeley, CA: Pacific Southwest Forest and Range 

Experiment Station, Forest Service, U.S. Department of Agriculture; 9 p. 

Wagener, Willis W. 1965. Dwarfmistletoe removal and reinvasion in Jeffrey and ponderosa pine, northeastern California. Res. Note PSW-73. 

Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, 

Forest Service, U.S. Department of Agriculture; 8 p. 

USDA Forest Service Res. Paper PSW-RP-207. 1992. 

Printed on Recycled Paper 

Research Paper 

PSW-RP-207