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Disease Control and Pest Management

Evaluation of New Biotypes of Trichoderma harzianum for Tolerance to Benomyl and Enhanced Biocontrol Capabilities. G. C. Papavizas, Plant pathologist, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Beltsville, MD 20705; J. A. Lewis(2), and T. H. Abd-El Moity(3). (2)(3)Soil scientist, and plant pathologist, respectively, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Beltsville, MD 20705, (3)Permanent address: Plant Pathology Institute, Agricultural Research Center, Ministry of Agriculture, Giza, Egypt. Phytopathology 72:126-132. Accepted for publication 14 May 1981. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1982. DOI: 10.1094/Phyto-72-126.

Aqueous suspensions of conidia of Trichoderma harzianum wild strain WT-6 were placed on V-8 juice agar and exposed to ultraviolet (UV) radiation for 100 min. Conidia of WT-6 from surviving colonies of the first irradiation were allowed to germinate on the agar before a second exposure to UV for 100 min. The irradiated plates were incubated at 25 C under fluorescent light, and the resulting colonies of T. harzianum were isolated and grown on the medium. Conidia from the colonies that survived the second irradiation were placed on agar and UV-irradiated for 100 min. Of 36 colonies that survived the three irradiations, 19 colonies from the third series tolerated high concentration of benomyl (100500 mg/ml) as indicated by growth in solid and liquid media and conidial germination tests on benomyl-amended agar. The UV-induced biotypes differed considerably from WT-6 in appearance, growth habit, fungitoxic metabolite production against a given assay pathogen (Sclerotium cepivorum), and ability to survive in soil. Certain UV-induced biotypes that were also tolerant to benomyl suppressed the saprophytic activity of Rhizoctonia solani in soil more effectively than did the wild strain. Several UV-induced biotypes were consistently more effective than the wild strain WT-6 in suppressing damping-off (Pythium ultimum) of peas, damping-off (R. solani) of cotton and radish, and white rot (S. cepivorum) of onion.