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Penetration of Sclerotia of Sclerotium rolfsii by Trichoderma spp.. Y. Henis, Professor, Department of Plant Pathology and Microbiology, Faculty of Agriculture, Hebrew University, P.O.B. 12, Rehovot 76100, Israel; P. B. Adams(2), J. A. Lewis(3), and G. C. Papavizas(4). (2)(4)Plant pathologists, Soilborne Diseases Laboratory, Plant Protection Institute, U.S. Department of Agriculture, Beltsville, MD 20705; (3)Soil scientist, Soilborne Diseases Laboratory, Plant Protection Institute, U.S. Department of Agriculture, Beltsville, MD 20705. Phytopathology 73:1043-1046. Accepted for publication 16 February 1983. 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-73-1043.

Penetration of sclerotia of Sclerotium rolfsii by Trichoderma isolates was followed by a direct and an indirect approach. Sclerotia were immersed in an aqueous suspension of Trichoderma conidia (1.5 x 107/ml) and incubated on water agar or on soil. Periodically, sclerotial samples were surface sterilized with 1% sodium hypochlorite solution for 2 min, washed, and plated out on a selective medium for Trichoderma and on a medium that allowed germination of sclerotia only. When the sclerotia were preincubated on either agar or soil, Trichoderma isolates differed in their ability to penetrate the sclerotia. Penetrated sclerotia that showed different stages of degradation were fixed, sectioned, stained, and examined with a light microscope. Hyphae of Trichoderma penetrated the rind and cortex, lysed the medullar tissue, produced chlamydospores inside and conidia outside the sclerotia, and finally underwent autolysis. Degraded sclerotia became dark in color, soft, and empty, and disintegrated under slight pressure. Sclerotia that were allowed to be penetrated on agar without being degraded and that were further incubated in soil, retained their firmness and were not degraded by the penetrating antagonist. Penetration capacity is an important but not the only property required for Trichoderma isolates to be efficient biocontrol agents.