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Appl. Environ. Microbiol., May 1996, 1550-1557, Vol 62, No. 5
CM Craft and EB Nelson
Composts prepared from a variety of feedstocks were tested for their
ability to suppress seedling and root diseases of creeping bentgrass caused
by Pythium graminicola. Among the most suppressive materials in laboratory
experiments were different batches of a brewery sludge compost and a
biosolids compost from Endicott, N.Y. Batches of these composts that were
initially not suppressive to Pythium damping-off became more suppressive
with increasing compost age. Leaf, yard waste, food, and spent mushroom
composts as well as certain biosolids, cow manure, chicken-cow manure, and
leaf-chicken manure composts were not suppressive to Pythium damping-off.
In some cases, turkey litter, chicken manure, chicken-leaf, and food waste
composts were inhibitory to creeping bentgrass seed germination in
laboratory experiments. Microbial populations varied among all of the
composts tested. Bacterial populations were high in all composts except the
turkey litter compost, in which populations were 1,000- to 10,000-fold
lower than in the other composts tested. Among the highest populations of
heterotrophic fungi and antibiotic-producing actinomycetes were those found
in all batches of the brewery sludge compost, whereas the lowest
populations were found in turkey litter, chicken manure, and food waste
composts. Heat treatment of suppressive composts reduced populations of
bacteria, fungi, and actinomycetes in all composts tested. Disease
suppressiveness was also reduced or eliminated in heated composts. Amending
heated composts with small amounts of nonheated compost restored
suppressive properties and partially restored microbial populations to
wild-type levels. A strong negative relationship between compost microbial
activity (as measured by the hydrolysis of fluorescein diacetate) and
Pythium damping-off severity was observed. When composts were applied to
creeping bentgrass in field experiments, a significant level of
suppressiveness was evident with some composts when disease pressure was
high (i.e., disease ratings high in uninoculated plots). A 1991 batch of
turkey litter compost and the 1990 batch of Endicott biosolids were
consistently suppressive to foliar symptoms of Pythium root rot on creeping
bentgrass. This study indicates that suppression of Pythium diseases of
creeping bentgrass in batches of brewery sludge and Endicott biosolids
composts, and possibly in other suppressive composts examined in less
detail in this study, is related directly to the microbial activities in
the composts. On the other hand, the mechanisms of Pythium suppression in
turkey litter and perhaps other poultry-based composts is not related
directly to the compost microbial activity. Although turkey litter showed a
lack of suppressiveness in laboratory bioassays and low microbial
populations and activity, it resulted in a significant and consistent level
of suppressiveness in field experiments. Therefore, the microbiological
properties of Pythium-suppressive composts may differ substantially, and
measurements of microbial populations and activity may not be predictive of
the level of disease suppression in all composts.
Copyright © 1996, American Society for Microbiology
Microbial Properties of Composts That Suppress Damping-Off and Root Rot of Creeping Bentgrass Caused by Pythium graminicola
Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14853
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