Factors Affecting Germinability and Susceptibility to Attack of Sclerotia ofSclerotium rolfsiibyTrichoderma harzianumin Field Soil

Publisher Website
Google Scholar
Abstract
Fresh, soil-produced and PDA[potato dextrose agar]-produced sclerotia of S. rolfsii were exposed to drying, washing, NaClO (1% solution), metham-sodium, and heat shock treatments. The treated sclerotia were immersed in spore suspensions of T. harzianum (WT-6) and incubated on field soil and on PDA supplemented with 10 .mu.g of 8-hydroxyquinoline (PDA-8HQ)/ml. 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 .ltoreq. 30% (.ltoreq. 7.12 mm Hg) for 24-48 h, to .gtoreq. 100 .mu.g of metham-sodium/g of soil for 1-4 h, and to localized heat treatment of 90.degree. C for 15 s, 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 80-1000 .mu.g of fumigant/g of soil for 1-4 h or with 20 .mu.g/g for 16 h in field soil. Treatment of sclerotia with metham-sodium before inoculation with 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.