VIEW ARTICLE

Disease Control and Pest Management

Physiological and Biocontrol Characteristics of Stable Mutants of Trichoderma viride Resistant to MBC Fungicides. G. C. Papavizas, Plant pathologist, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705; J. A. Lewis, soil scientist, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705. Phytopathology 73:407-411. Accepted for publication 8 September 1982. 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, 1983. DOI: 10.1094/Phyto-73-407.

Aqueous suspensions of conidia of Trichoderma viride wild strain T-1 were placed on V-8 juice agar and exposed to ultraviolet (UV) radiation for 80 min. The 10 colonies (biotypes) that survived the irradiation tolerated high concentrations (up to 100 μg of active ingredient per milliliter) of benomyl, thiabendazole, and thiophanate-methyl, as indicated by growth in fungicide-amended potato-dextrose broth and conidial germination tests on benomyl-amended V-8 juice agar. The UV-induced biotypes differed from T-1 in appearance, sporulation habit, and ability to grow in a liquid medium at various pH values. The wild strain and all biotypes grew and sporulated better in a synthetic medium adjusted to pH 3.5 and 4.5 than at higher pH values. In dual cultures with eight soilborne plant-pathogenic fungi, biotypes R3 and R4 inhibited growth of five of the eight pathogens tested. Two biotypes (R1 and R2) inhibited growth of Fusarium oxysporum f. sp. melonis only. The wild strain and the remaining biotypes did not produce any zones of inhibition against the eight pathogens tested. Several UV-induced biotypes (R4 and R6) were more effective than the wild strain T-1 in suppressing damping-off (Pythium ultimum) of peas when their conidia were applied as seed treatments. Two UV-induced biotypes (R5 and R6) significantly suppressed the level of damping-off and blight on beans (Sclerotium rolfsii) compared to the level of the control, and suppression by the two biotypes was significantly better than that by the wild strain.