Research Nate som267

1981

Benomyl Stimulates Ectomycorrhizal Development by Pisolithus

Tinctorius on Shortleaf Pine Grown in Containers’

William H. Pawuk, and James P. Barnett

SUMMARY

Container-grown shortleaf pine (Pinus echinata

Mill.) seedlings inoculated with Pisolithus tinctorius

and drenched with benomyl formed more mycorrhizal roots than undrenched seedlings. Seedlings were

drenched (2.5, 5, and 10 mg ai in 15 ml of water

per individual) prior to sowing and at either 2-, 4-,

or 8-week intervals. Pisolithus formed best at the

highest benomyl level, 10 mg every 2 weeks. Benomyl application increased seedling diameter, height,

and weight. Highest benomyl dosages produced the

largest seedlings.

Addltlonal keywords: Pinus echinata, containerized seedlings, seedling size and weight, growing

medium.

INTRODUCTION

A recent study (Pawuk et al. 1980) evaluated the

effects of several fungicides on mycorrhizal formation by Pisolithus tinctorius [( Pers.) Coker and Couch]

on container-grown longleaf pine (Pinus palustris

Mill.) in milled pine bark. Benomyl 50 WP, methyl

1-(butylcarbamoyl)-2-benzimidazole carbamate, apl Mention of trade names is for information only and does not

constitute endorsement by the USDA Forest Service.

plied at 5 mg ai per seedling every 4 weeks, significantly increased mycorrhizal formation over the

control. Modifications of dosage levels and drenching

schedules might theoretically identify treatments

to further enhance mycorrhizal development.

Although the original study was done using a pine

bark medium, peat-vermiculite mixes are more commonly used in container culture (Tinus and McDonald

1979). Pisolithus develops well in a peat-vermiculite

medium (Marx and Barnett 1974, Ruehle and Marx

1977) but the effect of benomyl on mycorrhizal development is untested in this medium.

This experiment was initiated to test the effect of

benomyl in stimulating mycorrhizal development on

shortleaf pine (Pinus echinata Mill.) in a peat-vermiculite medium and to identify effective drench rates

and schedules.

METHODS

This study was designed as a randomized complete-block design with four replications. Stratified

seeds of shortleaf pine were sown into SpencerLemaire Rootrainers (164 cm* per cavity). Cavities

contained equal parts of peat and vermiculite with

vegetative inoculum of Pisolithus tinctorius (Isolate

138) prepared according to Marx and Bryan (1975)

added at 1 to 8 parts of medium. Seedlings were

thinned to one per cavity 3 weeks after sowing and

extra seedlings were then transplanted to containers

Southern Forest Experiment Station/T-l0210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, Eastern Oklahoma, Tennessee, Eastern Texas.

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having germination failures. Sixteen seedlings were

grown for each treatment replication.

Total treatment combinations consisted of three

dosage levels and three time intervals (nine treatment combinations) and an untreated control. Seedlings were drenched with 2.5, 5.0, and 10.0 mg of

benomyl per seedling before sowing and at either 2-,

4-, or 8-week intervals. Seedlings receiving no benomyl were grown as a control. All were fertilized at

3-week intervals after transplanting with a 2500 ppm

solution of N-P-K fertilizer (20-19-18) which was

applied to saturation.

Ten seedlings were randomly selected from each

treatment-replication and the percentage of Pisolithus-infected short roots was estimated for each

seedling 18 weeks after sowing. At that time, seedling diameter, height, and average dry weights were

also determined.

Data were analyzed by ANOV. Mean separation of

major effects was made using single degree of freedom tests while mean separation of minor effects

was made with Duncan’s multiple range tests. The

0.05 level was used to evaluate statistical significance

throughout the study.

RESULTS

Mycorrhizal Development. - Pisolithus tinctorius

formed mycorrhizae in all treatments. Control seedlings, with 8 percent, had least infection. Seedlings

drenched with high rates of benomyl and seedlings

receiving frequent drenchings generally formed the

most mycorrhizae (table 1). However, a dosage rate

x drench frequency interaction was present (table 2).

Seedlings drenched with 10 mg every 8 weeks did

not form more mycorrhizae than seedlings drenched

with 2.5 or 5.0 mg every 2 weeks. Furthermore,

no difference occurred between the 5- and lo-mg

rate at the 4-week drench. At 5 mg, more mycorrhizae formed at the 4-week schedule than at the 2-week

schedule, and mycorrhizal development did not differ

for the 4- and 8-week drenches at 2.5 mg.

During the study, seedlings received 5,10,20,40,

or 80 mg benomyl depending on drench schedule

and dosage rate. With one exception (table 3), mycorrhizal development increased with increased

amounts of benomyl. Regression analysis compared

total amount of benomyl applied (X) to mycorrhizal

development (Y). The calculated F equals 39.99,

r* equals 0.54, and Y equals 21.35 + 0.34X with percent mycorrhizal development expressed in transformed arc sine values.

Table 1 .-Mycorrhlzal development by Pisoiithus tinctorius end

growth of shortleef pine seedllngs drenched with

benomyl (me/n effects table)

Benomyl

dosage rate

mglseedllng

2.5

5.0

10.0

p.t. Diameter Height Dry weight

% infection mm cm mg

17.67’ 2.06 a2 13.54 a 462 b

24.00 2.04 a 13.26 a 476 b

36.67 2.12 a 13.60 a 506 a

Drench frequency

wk

2 34.33’

4 27.00

S 17.00

2.19a 14.44 a 531 a

2.06 b 13.92 a 402 b

1.96 b 12.24 b 435 c

Control 8.00 1.94 11.90 406

‘The dosage rate x drench frequency interaction was significant.

See table 2 for mean separation.

2Means followed by the same letter within columns are not significantly different at the 0.05 Level.

Seedling Growth. -Diameter and height, not influenced by dosage rate, were affected by drench

frequency. Although actual differences were small,

less than 0.2 mm, seedlings drenched every 2 weeks

had larger diameters than those drenched at 4 or 8

weeks (table 1). Differences between 4 and 8 weeks

were not significant. Height growth, consistent between the seedlings in the 2- or 4-week treatments,

was 16 percent taller than in seedlings drenched

every 8 weeks.

Seedling dry weights were affected by both dosage rate and drench frequency. Seedlings drenched

with 10 mg benomyl were heavier than those drenched

with 2.5 or 5 mg. Differences were not significant

Table 2.-Mycorrhizal development by Pisolithus tinctorius as

affected by benomyl dosage and drench frequency

(interaction table)’

Drench frequency

2.5

Dosage rate (mg)

5.0 10.0

wk -----------%infectjon ___________

2 25c 24~ 54a

4 16~ 31 b 34 b

0 128 17d 22c

‘Means followed by the same letter are not significantly different

at the 0.05 level.

William H. Pawuk was Research Plant Pathologist (now with Tongass NF, Petersburg, Alaska), James P. Barnett is Principal Siiviculturist,

Southern Forest Experiment Station, Forest Service-USDA, Pineville, La. 71360.

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between the 2.5 and 5-mg treatments. Dry weights

also significantly increased with increased drench

frequency. Increasing frequency of application from

8-to P-week intervals increased seedling dry weights

by 22 percent.

Table 3.-Mycorrhizal development by Pisolithus tinctorius on

shortleaf pine seedlings as influenced by total amount

of benomyl applied

Benomyl stimulated both mycorrhizal formation

and seedling growth. The growth response is probably due to control of soil fungi that reduce seedling

growth or to effect of increased mycorrhizal development on benomyl-treated seedlings. In all cases,

benomyl-treated seedlings were increasingly Iargot

when fungicide concentrations increased.

Dosage Number

rate drenches’

Total

benomyl

Mycorrhizal

development

mg

10 8

10 4

5 4

2.5 S

10 2

5 8

5 2

2.5 4

2.5 2

0 0

mg

8 0

2

2 0

2 0

4 0

10

IO

5

0

percent

5 4

3 4

31

25

2 2

2 4

17

18

12

8

‘Seedlings drenched every 2 weeks = 8,4 weeks = 4, and 8

weeks = 2.

DISCUSSION

This study supports previous findings (Pawuk et

al. 1980) that /? tirtctorius forms more mycorrhizae

with southern pine seedlings when benomyl is present in the soil or potting media than when it is

absent. A possible explanation is that benomyl inhibits the growth of antagonistic soil fungi. Soil fungi

such as Trichoderma and Pennicillium, antagonistic

to many fungi, are inhibited by low concentrations of

benomyl (Edgington et al. 1971).

Pisolithus appears to have a high tolerance to

benomyl and develops best when benomyl concentrations are high. Root pathogens such as Fusarium are common in container media growing

southern pine seedlings (Pawuk 1978, Pawuk and

Barnett 1974). Fusarium reduces root development

and growth and may kill seedlings. Healthy seedlings,

free of Fusarium, have vigorous root systems and

provide more sites for ectomycorrhizal infection.

Edgington, L. V., K. L. Khew, and G. L. Barron.

1971. Fungitoxic spectrum of benzimidazole compounds. Phytopathology 61: 42-44.

Marx, Donald H., and James P. Barnett.

1974. Mycorrhizae and containerized forest tree

seedlings. In: Proc. North Am. Containerized

Forest Tree Seedling Symp., Great Plains Agric.

Count. Publ. 68:85-92.

Marx, Donald H., and W. C. Bryan.

1975. Growth and ectomycorrhizal development

of loblolly pine seedlings in fumigated soil infested with the fungal symbiont Pisolithus tinctorius. Forest Sci. 21:245-254.

Pawuk, William H.

1978. Damping-off of container-grown longleaf

pine seedlings by seedborne Fusaria. Plant

Disease Reporter 62:82-84.

Pawuk, W. H., and J. P. Barnett.

1974. Root rot and damping-off of container grown

southern pine seedlings. In: Proc. North Am.

Containerized Forest Tree Seedling Symp.,

Great Plains Agric. Count. Publ. 68:173-l 76.

Pawuk, William H., John L. Ruehle, and Donald H.

Marx.

1980. Fungicide drenches affect ectomycorrhizal

development of container-grown Pinuspalustris

seedlings. Canadian J. For. Res. 10:61-64.

Ruehle, J. L., and D. H. Marx.

1977. Developing ectomycorrhizae on containerized pine seedlings. U.S. Dep. Agric. For. Serv.

Res. Note SE-242, 8 p. Southeast. For. Exp.

Stn., Asheville, N.C.

Tinus, Richard W., and Stephen E. McDonald.

1979. How to grow tree seedlings in containers in

greenhouses. U.S. Dep. Agric. For. Serv. Gem

Tech. Rep. RM-80, 256 p. Rocky Mt. For. and

Range Exp. Stn., Fort Collins, Colo.

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