Isolation and Biocontrol Potential ofTrichoderma hamatumfrom Soil Naturally Suppressive toRhizoctonia solani

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Abstract
A soil naturally suppressive to R. solani was collected from Colombia, South America. Suppressiveness was confirmed in the laboratory by comparing its conducive index (0.2) to that of a conducive Fort Collins clay loam (0.85). R. solani propagules repeatedly were added to both soils and the resultant disease incidence on radishes grown in the suppressive soil was lower (P = 0.01) than in comparable inoculations in the conducive Fort Collins clay loam. The Colombian soil contained 108 propagules of fungi/g of which 8 .times. 105 propagules/g was T. hamatum. When conidia of this fungus were placed in Fort Collins clay loam at 106 propagules/g, the soil became suppressive to R. solani. T. hamatum attacked the mycelium of R. solani when the 2 microorganisms were grown in 2-membered culture. It also produced the cell wall degrading enzymes .beta.-(1-3) glucanase and chitinase, but there was no detectable antibiotic activity in vitro when T. hamatum was added to conducive Fort Collins clay loam at 106 conidia/g soil. It became suppressive to R. solani not only on radishes but on beans as well. Such treatment also induced suppressiveness to Pythium spp. attacking peas, and Sclerotium rolfsii in beans.