Effect of Mycelial Preparations ofTrichodermaandGliocladiumon Populations ofRhizoctonia solaniand the Incidence of Damping-Off

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Abstract
Mycelial preparations of 8 of 14 isolates of Trichoderma spp. [T. viride, T. havzianum, T. hamatum] and Gliocladium virens reduced survival of R. solani at least 50% in pathogen-infested beet seed in soil and infested with sand/cornmeal inoculum of the pathogen. All isolates reduced saprophytic growth of R. solani from infested beet seed into soil. Isolates of T. hamatum and G. virens were more effective than those of T. harzianum and T. viride. Population densities of all isolates increased 104-106-fold during 3 wk of incubation after mycelial preparations were added to soil. Conidial preparation of isolates, added to soil in amounts equal to propagules in mycelial preparations, did not reduce survival of R. solani or its growth through the soil. Mycelial preparations, but not conidia, of most isolates of Trichoderma spp. and G. virens prevented damping-off of cotton, sugar beet and radish seedlings in the greenhouse. There was no correlation between population density of antagonists and pathogen survival of damping-off. There was a highly significant negative correlation between stand in all 3 crops and pathogen survival in soil.