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Survival of Trichoderma harzianum in Soil and in Pea and Bean Rhizospheres. G. C. Papavizas, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Beltsville, MD 20705; Phytopathology 72:121-125. Accepted for publication 17 February 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-72-121.

A semiselective medium was developed for the direct isolation of Trichoderma harzianum and other Trichoderma spp. from soil, and for the quantitative estimation of its inoculum density in soil. The selective agar medium contained per liter: V-8 juice, 200 ml; glucose, 1 g; agar, 20 g; and water, 800 ml. The agar was autoclaved separately in 0.5 L of water and added to the V-8 juice after autoclaving. The medium, which was designated as TME, contained the following antimicrobial agents (μg/ml): neomycin sulfate, bacitracin, penicillin G, and chloroneb, 100 each; nystatin, 20; chlortetracycline HCl, 25; sodium propionate, 500; and penta-chloronitrobenzene, 100. For benomyl-tolerant biotypes, the TME medium was supplemented with 10 μg/ml of benomyl. Conidia of T. harzianum that were added to soil without nutrient-supplying amendments survived for at least 130 days, but the duration and the percent survival depended on the isolate used. T. harzianum did not survive well in the rhizosphere of bean and pea seedlings when seed was coated with conidia of the fungus. It also did not increase in the rhizosphere of pea seedlings from conidia applied directly to soil 1 day before planting. Infusion of pea seed with the fungicide metalaxyl before coating it with conidia of T. harzianum improved survival of conidia in the rhizosphere compared with the survival in the rhizosphere from seed that received conidia only.

Additional keywords: biological control.