United States

Department of

Agriculture

Forest Service

Resistance of Loblolly

Pine Sources to Fusiform Rust

in Field Progeny Tests

Southeastern Forest

Experiment Station

Research Paper

SE-268

H.R. Powers, Jr.

E.G. Kuhlman
October 1987

Southeastern Forest Experiment Station

P.O. Box 2680

Asheville, North Carolina 28802
Resistance of Loblolly

Pine Sources to Fusiform Rust

in Field Progeny Tests

H.R. Powers, Jr., and E.G. Kuhlman

Research Plant Pathologists

Forestry Sciences Laboratory

Athens, Georgia

ABSTRACT

Three field progeny tests in Greene County,

Georgia, of 28 loblolly pine seed sources with possible resistance to fusiform rust indicated that all

sources had moderate to high resistance after 10 to 14

years in the field. Susceptible check sources had 86

and 78 percent rust infection after 13 and 14 years,

while the various seed sources had infection percentages ranging from 1 to 57. In one test, field infection of rust-free seedlings surviving the concentrated

basidiospore spray (CBS) inoculation system had a

correlation coefficient of r=0.85 with the original

CBS infection results. Generally, the CBS system correctly classified resistant and susceptible sources;

however, seven sources with field resistance were

classed as susceptible in the CBS system. Therefore,

field progeny tests will continue to play an important

role in evaluating rust-resistant pine sources.

Keywords: Pinus taeda, Cronartium quercuum, disease

resistance, artificial inoculation.

The identification and selec,tion of

loblolly (Pinus taeda L.) and slash (g.

elliottii Engelm. var. elliottii) pines

with genetically controlled resistance

quercuum (Berk.) Miyabe ex Shirai f. sp.

to fusiform rust, caused by Cronartium -~

fusiforme, has been underway for more

than 25 years (Barber 1961; Jewe:Ll and

Mallett 1967; Wells and Wakeley :1966).

Several methods have been used to identify sources of resistance. In the

Southwide Seed Source Study (Wel:Ls and

Wakeley 1966), mass collections of lob1011~ pine seeds from some geographic

areas were more resistant to fusiform

rust than collections from other areas.

Others observed performance of progeny

of rust-free phenotypes in field tests

or in artificial exposures to the rust

fungus (Dinus and Griggs 1975; Jewel1

and Mallett 1967; Powers 1980; Zobel and

others 1971). A major breakthrough was

the development of the concentrated

basidiospore spray (CBS) system, a

standardized artificial inoculation

system that made it possible to evaluate

hundreds of pine families (Matthews and

Rowan 1972). Miller and Powers (1983)

showed that results with the CBS system

correlate closely with,field test results for loblolly pine. Testing by the

CBS system is provided at the Resistance

Screening Center, maintained near Asheville, NC, by the Southern Region of the

Forest Service, U.S. Department of Agriculture. Forestry organizations across

the South routinely send seedlots to the

Center for evaluation of fusiform-rust

resistance.

In this paper, we describe three

tests involving seedlings from 24 halfsib families, 1 full-sib family, and 3

bulk collections of loblolly pine that

were outplanted in Greene County,

Georgia, to determine their relative

field susceptibility to fusiform rust.

All seed sources were originally

selected because field or greenhouse

test results indicated at least some

rust resistance. In one of the studies,

rust-free survivors of CBS inoculations

were outplanted, whereas in the other

two studies seedlings were not inoculated prior to outplanting. Field

performance of each family was compared

with its susceptibility as estimated by

the CBS system.
Methods

The three field tests were established in Greene County on land owned

by the Georgia Kraft Corporation. Two

plantings were contiguous and the third

was less than 1.6 km away. Sites were

clearcut and roller-chopped prior to

planting. Seedlings were all planted

at a 1.8- x 3.0-m spacing.

Test 1. Progeny of 11 half-sib

families and one geographic seed source

were inoculated with basidiospores in 10

early tests of the CBS system. Only

seedlings without galls after 1 year in

a greenhouse were selected for outplanting. Seedlings from the 13th source, the

susceptible check, were not subjected to

artificial inoculation prior to planting

in the field. However, in the 10 prior

CBS inoculations, 75 percent of seedlings of the susceptible source got

galls. Seedlings were hand-planted in

March 1973. There were eight replications with each replication containing

one lo-tree row of each family. Families were randomly assigned to rows

within replications in a randomized

block design. In November 1981 at age

9, galled trees and numbers of galls per

tree were tallied for each family. In

March 1987 at age 14, branch and stem

galls and d.b.h. were recorded.

Test 2. Six sources of uninoculated

seedlings were hand-planted in November

1973. Four sources are half-sib families and two are bulk collections. Each

of 12 replications consisted of an lltree row of each of the 6 sources. At

age 8 (1X31), numbers of galls per tree

were tallied for each family. At age 13

(1987). the presence of branch and stem

galls and d.b.h. were recorded for each

tree.

Test 3. Uninoculated seedlings from

18 sources were hand-planted in March

1977 in four replications, each containing one 20-seedling row of each

source. Seventeen sources are half-sib

progeny. while one source is Georgia

Kraft Corporation's improved loblolly

pine, which was used as a commercial

check. At age 10 (1987), the presence

of stem and branch galls and d.b.h. of

each tree were recorded.

Data for each test were analyzed

separately. Prior to statistical analysis, percentages of trees with rust

were transformed to arc sine values.

Analysis of variance (ANOVA) and

Duncan's multiple range tests were

carried out on both percentage and

transformed data.

Results

Overall tree survival was 92 percent

at age 14 in test 1 and 88 percent at

age 13 in test 2. Test 3 was on a

poorer site, and survival averaged 74

percent at age 10. The ANOVA indicated

that both incidence of rust galls and

d.b.h. values varied significantly by

family and seed source in each of the

three tests. There was an interaction

between diameter and replications in

tests 2 and 3, but there was no interaction of rust and replications in any

test.

Test 1. The incidence of rust galls

after 14 years ranged from 78 percent on

the susceptible checks to 1 percent on

trees in family SML-9 (table 1). All

pine seed sources had significantly less

rust than the susceptible check source.

These results verified those from the

CBS inoculations, which indicated that

all 12 sources were more resistant than

the susceptible check source. The

correlation coefficient between field

infection on these families at age 14

and the CBS inoculation results was

r=o.85. Families with high percentages

of trees infected also had high numbers

of galls per infected tree at age 9

years and high incidences of stem galls

at age 14.

There was no relationship between

diameter growth and rust susceptibility. Some of the largest average

d.b.h.'s occurred in both the most

susceptible and the most resistant seed

sources. Similarly, seed sources with

small average d.b.h. were found at both

ends of the susceptible-resistant

spectrum.

Test 2. The amount of rust infection

was similar to that in test 1. Infection at age 13 ranged from 3 percent in

2
family SML-9 to 86 percent in the susceptible check source (table 2). The

correlation coefficient between field

infection on these families and the CBS

inoculation results on other seedlings

of the same families was r=O.88 at age

13.

Test 3. There were no families with

very high levels of rust infection as

was the case in tests 1 and 2. One

reason was that a commercial con,trol

(Georgia Kraft improved loblolly) was

included in place of a susceptible

check. The commercial check was found

to be less susceptible to rust than we

had anticipated. The highest incidence

of rust (55 percent) occurred in family

601 (table 3). However, four half-sib

families that were planted in both tests

1 and 3 had very similar percentages of

galls: 31 and 38 percent for 4625-3, 28

and 32 percent for 10-5, 27 and 29

percent for 11-20, and 12 and 13 percent

for 10-6 in tests 1 and 3, respectively.

The correlation between the field results for this test and the CBS inoculation results on the same families (r=

0.48) was not as good as in the two

other tests.

Discussion

Of 28 possibly resistant sources of

loblolly pine planted in the three tests

in Greene County, all showed moderate to

high resistance to fusiform rust after

10 to 14 years in the field. Several of

these sources (10-5, 11-20, 7-56, 15-42)

have been shown to have field resistance

when planted on other sites in the

Southeastern United States (Miller and

Powers 1983; Powers and Kraus 1983;

Zobel and others 1971). Rust-free

survivors of CBS inoculations from six

families (SML-9, 10-6, 11-9, 11-20,

10-5, and 29R) used in test 1 were also

planted in a seedling seed orchard in

Baldwin County, Georgia (Powers and

Kraus 1983). All six families demonstrated good resistance on both sites.

After 5 years in the seedling seed

orchard, progeny of SML-9 had only 2

percent infection, whereas those of 29R

had 48 percent infection (Powers and

Kraus 1983). The 0.85 correlation

coefficient between field and greenhouse

results in test 1 indicates that survivors of highly resistant families will

have higher field resistance than those

from moderately resistant families.

Since the 28 resistant sources come from

a variety of geographic locations and

tree improvement programs, they should

have sufficient variation in mechanisms

of resistance to provide a broad genetic

base of resistance for use in diverse

plantings.

The CBS system is routinely used to

evaluate the relative rust resistance of

progeny from phenotypically resistant

parent trees, and our evaluations are

based on galls formed on seedlings 9

months after inoculation. The disease

ratio (DR) is computed as the percentage

of seedlings with galls in a test family

divided by the percentage of seedlings

with galls in the susceptible control

seedlot. In our studies, a test family

with a DR < 0.70 is considered resistant; those-with a DR > 0.70 are considered susceptible. On the basis of DR

L 0.70, 21 of the 28 resistant families

were properly identified as resistant by

the CBS system. However, three families

(SML-20 DR 0.79, 1495-18 DR 0.71, and

7-56 DR 0.82) were not identified as

resistant in the CBS inoculation tests.

In these instances, field performance

was definitely superior to the artificial inoculation test results. Since

the CBS system is not only a rigorous

test but also a conservative one, such

families can be misclassified. Families

with intermediate levels of resistance

in the field, such as SML-20 with 50

percent rust are often difficult to

classify by the CBS system. Family

1495-18, which was quite resistant in

the field, had a DR of 0.71 and narrowly

missed the resistant classification.

Family 7-56 also performed better in

a field planting in Houston County,

Georgia, and in test 3 than in the CBS

inoculation (Miller and Powers 1983).

In addition, Zobel and others (1971)

reported that progeny of this family had

good field resistance in seven progeny

tests. More research is needed to

determine why families like SML-20,

1495-18, and 7-56 are more resistant in

the field than in CBS tests. Progress

3
is being made in enhancing the CBS system by identifying symptoms that are

better correlated with field resistance

(Walkinshaw and others 1980).

The correlation (r=o.85) of CBS

greenhouse test results to the field

results in test 1 was very good. There

were still strong differences in resistance between families even though a portion of the susceptible population of

each family had been eliminated by the

CBS inoculation test. These results

show that CBS survivors of the most

resistant families are superior in

resistance to those from families with

moderate resistance. Exposing seedlings

to the rust by the CBS or other inoculation procedures and outplanting only

rust-free survivors eliminates many of

the most susceptible trees in a family

(Dinus and Griggs 1975; Powers 1980;

Powers and Kraus 1983; Schmidtling and

Walkinshaw 1985). Powers and Kraus

(1983) reported a correlation of r=o.76

between infection in the CBS system and

subsequent infection of rust-free survivors. Schmidtling and Walkinshaw

(1985) reported r2=18 percent (r=0.42)

for the regression equation of field

infection to inoculation test results.

Correlations between field infection and

inoculation test results tend to be high

when there is a wide range in susceptibility of the test families and low when

the families are similar in response to

rust.

In the present work, some families

with relatively low percentages of trees

infected, such as 11-16 (19 percent) had

a high number of rust galls on the trees

that did become infected. In contrast,

some families such as 1590-6, had a much

higher percentage of trees infected (57

percent) but only about half as many

galls per infected tree. The reason

for this result is unknown, but the

increase in galls per infected tree and

stem galls between studies 1 and 2 for

sources L.P. and 29R suggests that some

very susceptible individuals were

eliminated by using survivors of CBS

inoculation.

Diameter growth was fair on these

relatively poor sites. Granite outcroppings and gulleys in the study area

contribute to the poor-site quality.

The significant replication effect in

tests 2 and 3 was caused by the poor

sites. Some of the most resistant

sources (Hitchiti Hybrid, 7R, and 10R)

have slow growth rates that make them

less desirable silviculturally. However, most resistant sources had good

growth rates. Their growth is encourging and indicates that using these

families in rust-resistance programs

will not result in reductions in yield.

Acknowledgment

We thank the Georgia Kraft

Corporation for its assistance in

providing land for planting sites.
Table 1. --Relative susceptibilities to fusiform rust of progeny from 13 loblolly

pine sources (test 1) in a 1973 field planting of rust-free survivors in Greene

County, Georgia, and in CBS system seedling inoculations

Field plantinga

Pine b

source

Galls/ Trees with Trees with Diameter CBS disease

infected rust galls stem galls a t ratioC

tree at a t a t breast

age 9 age 14 age 14 height

Number --------Percent------- -cm

SML-9

Hitchiti hybrid

10-6

11-g

11-16

L.P.

11-20

10-5

4625-3

29R

1582-11

1590-6

Susceptible check

0.0

2.0

1.2

1.8

7.1 ;:‘6

z-g312

2.1

3.7

5.6

5

1 Ad

AB

1 2 ABC

1 4 ABCDE

1 9 BCD

26 CDEF

2 7 CDEF

28 CDEF

31 DEF

EF

;i F

G

H

1

0 Ad

AB

4 ABC

4 ABC

1 0 ABCDE

1 0 ABCD

1 3 CDE

1 6 DEF

20 DEF

1 2 BCDE

20 EF

F

G

15.2 BCDd

13.4 A

16.2 CDE

16.8 E

16.5 DE

16.9 E

14.7 B

16.3 CDE

16.8 E

14.6 B

16.3 CDE

15.1 BC

16.9 E

0.40

.36

938

.47

-36

.48

.37

.46

.51

.54

.52

.51

1.00

apercentages and d.b.h. based on 8 replications with 10 trees/source/

replication.

b

Susceptible check and Livingston Parish (L.P.) were bulk seed collections.

All others were half-sib progeny of the parent clone indicated. Susceptible

check seedlings were not first exposed to CBS inoculations and were not rustfree survivors.

'Disease ratio = Percentage of trees galled in test family/percentage of trees

galled in susceptible check.

d Within columns, numbers followed by the same letter are not significantly

different according to Duncan's multiple range test, P- -< 0.05.
Table 2. --Relative susceptibilities to fusiform rust of progeny from six loblolly

pine sources (test 2) in a planting established in 1973 in Greene County, Georgia,

and in CBS system inoculations

Field plantinga

Pine b Galls/

source infected Trees with Trees with Diameter

tree at rust galls stem galls a t

CBS disgase

ratio

a t a t at breast

age 8 we 13 age 13 height

Number --------Percent------ cm

SML-9 0 3 Ad 0 Ad 13.7 Ad 0.40

L.P. 2.9 2 1 B 6~ 14.9 c .48

1495-18

::;

2 6 B 7A 14.7 c .71

SML-20 ;:: C 27 B 15.0 c .79

29R 4.6 c 27 B 13.8 AB .,I59

Susceptible check 5.9 8 6 D 49 c 14.5 BC 1.00

aNburn ers based on 12 replications with 11 trees/source/replication.

b

Susceptible check and Livingston Parish (L.P.) were bulk seed collections. All

other sources were half-sib progeny of the parent clone indicated.

'Disease ratio = Percentage of trees galled in test family/percentage of trees

galled in susceptible check.

d

Within columns, numbers followed by the same letter are not significantly

different according to Duncan's multiple range test (p > 0.05).

6
Table 3. --Relative susceptibilities to fusiform rust of progeny from 18 loblolly

pine sources (test 3) in a lo-year-old planting established in Greene County,

Georgia

Pine

source

Trees Diameter at CBS disease

with rust abreast heighta ratio b

B-5-4

10R

10-6

BA l-2

7R

15-42

40R

48~

11-20

29R x 10-5

10-5

3906-21

7-56

4625-3

Georgia Kraft Improved

BA 2

3505-16

601

_Percent

cd

ii iB

13 ABC

1 6 BCD

2 1 BCDE

22 BCDE

26 BCDE

28 CDE

29 CDEF

29 CDEF

$

DEF

DEF

DEF

38 DEF

Z?

DEF

DEF

4.1 EF

55 F

-cm

9.3 ABCDd

8.7 A B

10.5 CDE

9.6 ABCDE

8.2 A

10.9

9.9 BCD:

9.3 ABCD

9.0 ABC

9.7 BCDE

10.4 CDE

9.4 ABCDE

10.6

9.9 BCE

9.6 ABCDE

10.0 BCDE

9.4 ABCDE

8.5 A B

--

0.51

.52

.85

.83

.61

.65

.74

:Z

.49

.67

.82

.68

26

.82

.82

aNburn ers based on 4 replications with 20 trees/source/replication.

b

Disease ratio = Percentage of trees galled in test family/percentage of trees

galled in susceptible check.

'Analysis of variance and Duncan's multiple range test were done on transformed data.

d

Numbers within columns followed by the same letter are not significantly different

according to Duncan's multiple range test, P- -< 0.05.
Literature Cited

Barber, John C. 1961. Growth, crown form, and fusiform

rust resistance in open-pollinated slash pine

progenies. pp. 97-104. In: Proceedings of the 6th

southern conference on forest tree improvement;

1.961 June 7-8; Gainesville, Fl.

Dinus, Ronald J.; Griggs, Margene M. 1975. Rust-free

slash pines surviving artificial inoculation

potentially useful for resistance breeding. Forest

Science 21:275-277.

Jewell, F.F.; Mallett, S.L. 1967. Testing slash pine

for rust resistance. Forest Science 13:413-418.

Matthews, Fred R.; Rowan, S.J. 1972. An improved

method for large-scale inoculations of pine and oak

with Cronartium fusiforme. Plant Disease Reporter

56:931-934.

Miller, T.; Powers, H.R., Jr. 1983. Fusiform rust

resistance in loblolly pine: artifical inoculation

vs. field performance. Plant Disease 67:33-34.

Powers, H.R., Jr. 1980. The use of survivors of

artificial inoculation tests in developing fusiform

rust resistant seed orchards. Phytopathologia

Mediterranea lV:l7-20.

Powers, H.R., Jr.; Kraus, J.F. 1983. Developing

fusiform rust-resistant loblolly and slash pines.

Plant Disease 67:187-189.

Schmidtling, R.C.; Walkinshaw, C.H. 1985. Fusiform

rust infection of loblolly pines that survived

resistance screening and of their progeny. Plant

Disease 69:491-493.

Walkinshaw, C.H.; Dell, T.R.; Hubbard, S.D. 1980.

Predicting field performance of slash pine families

from inoculated greenhouse seedlings. Res. Pap.

SO-160. New Orleans, LA: U.S. Department of

Agriculture, Forest Service, Southern Forest

Experiment Station. 6 pp.

Wells, Osborn 0.; Wakeley, Philip C. 1966. Geographic

variation in survival, growth, and fusiform-rust

infection of planted loblolly pine. Forest Science

Monograph 11. 40 pp.

Zobel, Bruce; Blair, Roger; Zoerb. Marvin. 1971. Using

research data--disease resistance. Journal of

Forestry 69:486-489.
l- -------------------------------l- ------------------------------- 1

i I I

I Powers. H-R., Jr.; Kuhlman, E.G. I Powers, H-R., Jr.; Kuhlman, E.G. I

I I

f

Resistance of loblolly pine sources to fusiform rust I Resistance of lobiolly pine sources to fusiform rust

I

I

in field progeny tests. Res. Pap. SE-268. Asheville, in field progeny tests. l?es. Pap. 5X-268. Ashetiille, I

I NC: U.S. Department of Agriculture, Forest Service, I NC: U.S. Department of Agriculture, Forest Service, I

I Southeastern Forest Experiment Station; 1987. 8 pp.

f

f

Southeastern Forest Experiment Station; 1987. 8 pp.

I

I

Results of concentrated basidiospore spray (CBS) inocuI

Results of concentrated basidiospore spray (CBS) inocu- 1

I

lations correlated well with field infection. Generally, lations correlated well with field infection.

I

Generally, I

I the CBS system correctly classified resistant and susI

ceptible sources, but it classed seven sources with field

resistance as susceptible. I

the CBS system correctly classified resistant and sus- I

ceptible sources, but it classed seven sources with field I

I

resistance as susceptible. I

I I

I

I

KEYWORDS: Pinus taeda, Cronartium quercuum, disease

I

KEYWORDS: Pinus taeda, Cronartium quercuum, disease I

I

resistance, artificial inoculation. resistance, artificial inoculation.

I

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l- -------------------- -------- L --_--------------------------- i
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