VIEW ARTICLE

Ecology and Epidemiology

Factors Affecting Germinability and Susceptibility to Attack of Sclerotia of Sclerotium rolfsii by Trichoderma harzianum in Field Soil. Y. Henis, Professor, Department of Plant Pathology and Microbiology, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O.B. 12, Rehovot 76100, Israel; G. C. Papavizas, plant pathologist, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705. Phytopathology 73:1469-1474. Accepted for publication 4 May 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-73-1469.

Fresh, soil-produced, and PDA-produced sclerotia of Sclerotium rolfsii were exposed to drying, washing, NaClO (1% solution), metham-sodium, and heat shock treatments. The treated sclerotia were immersed in spore suspensions of Trichoderma harzianum (WT-6) and incubated on field soil and on potato-dextrose agar (PDA) supplemented with 10 μg of 8-hydroxyquinoline (PDA-8HQ) per milliliter. Sclerotia were examined for ability to germinate on PDA-8HQ, the ability of WT-6 to sporulate on their surface, and for their eventual degradation. Naturally or artificially produced fresh sclerotia neither germinated nor were they attacked by WT-6 in field soil. Exposure of sclerotia to a relative humidity of ≤30% (≤7.12 mm Hg) for 24- 48 hr, to ≥100 μg of metham-sodium per gram of soil for 1- 4 hr, and to localized heat treatment of 90 C for 15 sec, triggered their germination in field soil and increased their susceptibility to degradation by WT-6. Germination of the pretreated sclerotia in soil was mainly of the eruptive type except following NaClO treatment. An additive effect of metham-sodium pretreatment and WT-6 inoculation was demonstrated with 80- 1,000 μg of fumigant per gram of soil for 1- 4 hr or with 20 μg/g for 16 hr in field soil. Treatment of sclerotia with metham-sodium before inoculation with T. harzianum (WT-6) resulted in an increase in sporulation of WT-6 on the sclerotia and an increase of susceptibility of sclerotia to degradation by the antagonist. This treatment also resulted in a lag phase longer than that of untreated sclerotia germinated on an agar medium.