THE INFLUENCE OF NUTRIENTS ON DEVELOPMENT, RESTING HYPHAE AND ALEURIOSPORE INDUCTION OF THIELAVIOPSIS-BASICOLA

Two isolates of Thielaviopsis basicola, one from tobacco and one from cotton, were grown in crude host root extracts at varied dilutions. As pects of hyphal morphology including hyphal diameter, hyphal length, a nd degree of branching were positively correlated with the level of av ailable nutrients under these conditions. Atypical hyphal forms were p roduced by ?: basicola under conditions of nutrient stress, and these forms were similar to two cultural mutants previously reported. Second ary chlamydospores also were ob served under nutrient stress condition s. Hyphal segments that possessed cytological and morphological featur es analogous to endoconidia and aleuriospores of T. basicola were obse rved during later stages of culture development under nutrient conditi ons favorable for growth and reproduction. These structures were terme d ''resting hyphae'' because T. basicola grew from them upon restorati on of nutrients when other regions of hyphae were no longer viable. Na tural and simulated depletion of nutrients in the culture environment following a period of vegetative growth induced aleuriospore productio n. Development of aleuriospores under these culture conditions demonst rated that ?: basicola is able to produce a substantial number of repr oductive structures from nutrient reserves held within the existing th allus.