The influence of nutrients on development, resting hyphae and aleuriospore induction of Thielaviopsis basicola

Abstract

Two isolates of Thielaviopsis basicola, one from tobacco and one from cotton, were grown in crude host root extracts at varied dilutions. Aspects of hyphal morphology including hyphal diameter, hyphal length, and degree of branching were positively correlated with the level of available nutrients under these conditions. Atypical hyphal forms were produced by T. basicola under conditions of nutrient stress, and these forms were similar to two cultural mutants previously reported. Secondary chlamydospores also were observed under nutrient stress conditions. Hyphal segments that possessed cytological and morphological features analogous to endoconidia and aleuriospores of T. basicola were observed during later stages of culture development under nutrient conditions favorable for growth and reproduction. These structures were termed “resting hyphae” because T. basicola grew from them upon restoration of nutrients when other regions of hyphae were no longer viable. Natural and simulated depletion of nutrients in the culture environment following a period of vegetative growth induced aleuriospore production. Development of aleuriospores under these culture conditions demonstrated that T. basicola is able to produce a substantial number of reproductive structures from nutrient reserves held within the existing thallus.

Key Words:

• Chalara elegans
• chlamydospore
• hemibiotroph