U.S. Department of Agriculture

Forest Service Research Note S E -318 September 1982

Fusiform Rust Infection of Loblolly and Slash Pines After

Artificial Inoculation and Natural Exposure in Plantations

by Earl R. Sluder and H. R. Powers, Jr.'

Abstract.--Seedlings from progenies of slash and loblolly -_------

pines were divided into two groups. One group was exposed

to the fusiform rust fungus in greenhouse inoculations by

the concentrated basidiospore spray system and the other

was exposed to natural infection in field progeny tests.

Within families, correlations between percentages of seedlings infected after field and artificial exposure were 0.6

to 0.8 for three slash pine plantations and 0.4 to 0.6 for

six loblolly pine plantations. Most progenies were highly

susceptible to infection, particularly under artificial

conditions. Greenhouse inoculations usually identified

highly resistant progenies but not those with small amounts

of resistance.

Keywords: Cronartium guercuum f. sp, fusiforme Pinus -__---_--- ---------y -----

elliottii Pinus taeda -_-------3 ----- -----.

With the rapid growth in plantation developed by Matthews and Rowan, called

forestry in the South has come a dras- the concentrated basidiospore spray

tic increase in losses caused by the (CBS) system, rapidly screens large

southern fusiform rust fungus (Cronartium quercuum (Berk.) Miyabe ex Shirai

f. sp. fusiforme) in plantings of slash

(Pinus elliottii Engelm. var. elliottii) and loblolly taeda L.) pines (p.

(Czabator 1971; Powers and others 1975;

Schmidt and others 1974; Sluder 1977).

Pine parents that bear rust-resistant

progeny are badly needed, but such

trees are rare.

To identify resistant trees, techniques for inoculating seedlings have

been developed (Jewel1 1960; Snow 1968;

Matthews and Rowan 1972). The method

1

Sluder is a Research Forester, Macon, Georgia; Powers is a Supervisory

Research Plant Pathologist, Athens,

Georgia.

numbers of seedlings from selected

trees for resistance to fusiform rust.

Trays of seedlings from the selected

trees are sprayed with controlled

volumes of a water suspension of basidiospores of known concentration, incubated in a moist chamber at 70' F, then

placed in a greenhouse. The percentages of seedlings with galls are recorded 6 months later for slash pine or

9 months later for loblolly pine. From

120 to 200 seedlings of each progeny

are inoculated, and at least one standard susceptible check lot is included

in each run. Under the conditions of

the test, progenies are consistently

ranked as resistant, intermediate, or

susceptible (Powers 1974), but the relationships between CBS ranking and

Southeastern Forest Experiment Station-Asheville, North Carolina
field resistance have not been adequately studied. This paper describes

a study of such relationships for

several groups of slash and loblolly

pine progeny in plantations in central

and west-central Georgia.

MATERIALS AND METHODS

This study on the application of the

CBS screening method was done cooperatively by the Tree Improvement Project

at Macon, Georgia, and the Diseases of

Southern Pines Project at Athens,

Georgia. Nine plantations established

between 1961 and 1974 were studied

(table 1). Progenies were from controlled pollinations of clones of loblolly and slash pines in a seed

orchard. Three plantations (57,

122-123, and 76) contained progenies

from pollinations with a mix of pollen

from several male parents; the other

six plantations contained single-cross

progenies.

Table l.--Study materials, test

The field design of the plantations

was randomized blocks with plot sizes

of 5, 16, or 25 trees and 4 to 10 replications. In individual plantations,

from 15 to 140 trees per progeny were

scored for rust symptoms (table 1).

Most trees were 5 to 6 years old when

scored, but those in one plantation

were 3 years old.

Seeds in excess of needs for establishing the plantations were labeled

and stored in a freezer. These stored

seeds were used in CBS inoculation

tests. However, not enough stored

seeds were available for two of the

plantations, numbers 57 (slash) and 76

(loblolly). In order to approximate

these progenies, which were from a pollen mix used on the female parents, we

collected wind-pollinated seeds from

the female parents in the seed orchard.

These progenies should closely approximate those in the field.

In the field, there was no replication of progeny sets over time, but

areas, and conditions for artificial

inoculations and field tests in Georgia

Field test Greenhouse test

Plantation

Age Inoculum Number

Year scored Trees/ density Seedlings/ of

Number County planted (years) progeny (M/ml) progeny progenies

SLASH PINE

57 Bleckley 1961 5 140 50 72 16a

78 Houston 1965 5 40 13 125 28

122-123 Bleckley 1972 3 70 13 125 17b

LOBLOLLY PINE

76 Bleckley 1965 5 120 75 110 14a

95 Putnam 1967 5 15 75 100 14

96 Troup 1967 5 15 75 100 14

104 Putnam 1969 6 40 75 115 9

105 Heard 1969 6 40 75 115 9

131 Houston 1974 5 60 50 160 43

a

For artificial inoculations, these progenies were approximately reconstituted by collecting wind-pollinated seeds from the appropriate clones in the

seed orchard.

b

These progenies were distributed in two adjacent plantations, with some

progenies common to both. The data were adjusted for combined analysis.

2
there was some replication over location. The 14 progenies in plantations

95 and 96 were the same. Also, the

nine in plantations 104 and 105 were

the same (table 1).

Seedlings were artificially inoculated at age 6 weeks with basidiospores

from a central Georgia source of 5.

quercuum f. sp. fusiforme. The inoculum densities used are listed in table

1. The number of seedlings screened

per progeny varied from 72 to 160 for

the different plantations (table 1).

Susceptible checks were used. Disease

ratio (DR)--percentage of test lot

infected divided by percentage of

susceptible check lot infected--was

calculated for all the progenies except

those in loblolly plantation 131.

Linear regressions and correlation

coefficients were computed for each

plantation to determine the relationship between field infection percentages and CBS screening DR (CBS

screening infection percentages for

progenies in plantation 131).

RESULTS AND DISCUSSION

Figure 1 shows data points and regression lines for one slash and one

loblolly pine plantation. In these and

PLANTATION 96 (LOBLOCLY,

t

in other plantations, progenies with

relatively low DR in greenhouse tests

had relatively low infection rates in

the field. Thus, the greenhouse tests

were reliable for identifying progenies

with large amounts of resistance. Most

of the progenies of both species were

highly susceptible to infection, particularly when artificially inoculated.

That is to be expected, since the

parents of these progenies were not intensively selected for resistance to

fusiform rust. Despite the high overall levels of susceptibility, significant correlations between natural and

artificial infection results were found

for all three slash pine plantations

and for three of the six loblolly pine

plantations (table 2). Similar studies

using other inoculation techniques have

been done on slash pine with results

similar to our slash pine results

(Dinus 1969; Goddard and Schmidt 1971).

The relationship between CBS and

field results was very similar for

progenies in paired plantations 95 and

96 and for progenies in paired plantations 104 and 105. Average field infection levels in plantations 95 and 96

differed by only 3 percentage points;

in plantations 104 and 105, however,

the difference was 22 percentage points

PLANTATION 57 (SLASH,

100

0

4 0 2 0 4 O S 0.8 1.0 12 1 4

INOCULATION DISEASE RATIO INOCULATION DISEASE RATIO

Figure 1. --Data points and correlation coefficients for one slash and one

loblolly pine plantation, showing the relationship between inoculation

disease ratio, a measure of infection based on a susceptible check lot,

and field infection percentage.
(table 2). This consistency in correlation between CBS and field results

for progenies planted in different locations is encouraging, particularly

for plantations 104 and 105, which

differed so much in average infection

levels.

CBS inoculation is done under controlled conditions, but conditions in

the field vary greatly over time and

space. Sources of field variation

include inoculum level, genetic makeup

or virulence of the fungus (Powers

1980; Powers and others 1977), temperature and moisture, and the coincidence

of optimum conditions for infection

with inoculum levels. If progenies

being tested ranked differently under

different field conditions, the accuracy of CBS screening for predicting

field performance will be impaired.

There is evidence that loblolly pine

progenies may not rank the same with

CBS screening at different inoculum

densities (Matthews and others 1978).

In the present study, the few progenies

with field resistance were accurately

identified by CBS screening. In fact,

the method appears to be conservative

in picking out field resistant progenies in that only the very best are

identified. The rating of almost all

tested progenies as susceptible is

discouraging in large-scale screenings

however. Perhaps refinements in the

screening method (Walkinshaw and others

1980) could increase its ability to

detect progenies with a moderate level

of field resistance. Also, as resistance genes accumulate in breeding populations, a greater range in resistance

likely will develop, making the screening method more effective.

Table 2. --Average disease ratio (DR) for slash and loblolly

pines in greenhouse inoculations, average percentage of

seedlings infected in plantations, and correlation between

greenhouse and field results

Plantation Correlation

Plantation Greenhouse mean % coefficient

number mean DR infection (r)

SLASH PINE

57 1.03

78 1.21

122-123 1.22

69 0.84**

97 .68**

62 .62**

LOBLOLLY PINE

76 1.07 92 .51NS

95 1.03 46 .56*

96 1.03 43 .63*

104 1.04 55 .50NS

105 1.04 77 .42NS

131 76(%) 82 .42**

* Significant at the 0.05 level.

** Significant at the 0.01 level.

NS = Not significant.
LITERATURE CITED

Czabator, Felix J. Fusiform rust of

southern pines - a critical review.

Res. Pap. SO-65. New Orleans, LA:

U.S. Department of Agriculture,

Forest Service, Southern Forest

Experiment Station; 1971. 39 p.

Dinus, Ronald J. Testing slash pine

for rust resistance in artificial and

natural conditions. In: Proceedings

of the tenth southern conference on

forest tree improvement; 1969 June

17-19; Houston, TX; Publ. 30. Macon,

GA: Southern Forest Tree Improvement

Committee, Eastern Tree Seed Laboratory; 1969: 98-106.

Goddard, R. E.; Schmidt, R. A. Early

identification of fusiform rust resistant slash pine families through

controlled inoculation. In: Proceedings: eleventh conference on southern

forest tree improvement; 1971 June

15-16; Atlanta, GA; Publ. 33. Macon,

GA: Southern Forest Tree Improvement

Committee, Eastern Tree Seed Laboratory; 1971: 31-36.

Jewell, F. F. Inoculation of slash

pine seedlings with Cronartium fusiforme. Phytopathology 50(l): 48-51;

1960.

Matthews, F. R.; Miller, T.; Dwinell,

L. D. Inoculum density; its effect

on infection by Cronartium fusiforme

on seedlings of slash and loblolly

pine. Plant Dis. Rep. 62: 105-108;

1978.

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

improved method for large-scale inoculations of pine and oak with

Cronartium fusiforme. Plant Dis.

Rep. 56: 931-934; 1972.

Powers, Harry R., Jr. Breakthrough in

testing for fusiform rust resistance.

For. Farmer 33(4): 7-8; 1974.

Powers, H. R., Jr. Pathogenic variation among single-aeciospore isolates

of Cronartium quercuum f. sp. fusiforme. For. Sci. 26: 280-282; 1980.

Powers, H. R., Jr.; McClure, J. P.;

Knight, H. A.; Dutrow, G. F. Fusiform rust: forest survey incidence

data and financial impact in the

South. Res. Pap. SE-127. Asheville,

NC: U.S. Department of Agriculture,

Forest Service, Southeastern Forest

Experiment Station; 1975. 16 p.

Powers, H. R., Jr.; Matthews, F. R.;

Dwinell, L. D. Evaluation of pathogenic variability of Cronartium fusiforme on loblolly pine in the

Southern USA. Phytopathology 67:

1403-1407; 1977.

Schmidt, R. A.; Goodard, R. E.; Hollis,

C. A. Incidence and distribution of

fusiform rust in slash pine plantations in Florida and Georgia. Tech.

Bull. 763. Gainesville, FL: Univ. of

Florida Institute of Food and Agricultural Science; 1974. 21 p.

Sluder, Earl R. Fusiform rust in lob1011~ and slash pine plantations on

high-hazard sites in Georgia. Res.

Pap. SE-160. Asheville, NC: U.S.

Department of Agriculture, Forest

Service, Southeastern Forest Experiment Station; 1977. 10 p.

Snow, G. A. Time required for infection of pine by Cronartium fusiforme

and effect of field and laboratory

exposure after inoculation. Phytopathology 58: 1547-1550; 1968.

Walkinshaw, C. H.; Dell, T. R.;

Hubbard, S. D. 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; 1980. 6 p.


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