I Chet, J Katan

An isolate of Trichoderma harzianum capable of lysing mycelia of Sclerotium rolfsii and Rhizoctonia solani was isolated from a soil naturally infested with those pathogens. In culture, T. harzianum grew better than S. rolfsii and invaded its mycelium under growth conditions adverse to the pathogen; eg, high pentachloronitrobenzene concentrations, high pH levels, or low temperatures. Under greenhouse conditions, incorporation of the wheat-bran inoculum preparation of T. harzianum in pathogen-infested soil significantly reduced bean diseases caused by S. rolfsii, R. solani, or both, but its biocontrol capacity was inversely correlated with temperature. The wheat bran preparation of T. harzianum increased growth of bean plants in a noninfested soil and it controlled S. rolfsii more efficiently than a conidial suspension of the same antagonist. An uninoculated wheat bran preparation increased disease incidence. In naturally infested soils, wheat bran preparations of T. harzianum inoculum significantly decreased diseases caused by S. rolfsii or R. solani in three field experiments with beans, cotton, or tomatoes, and they significantly increased the yield of beans.