EFFECT OF NUTRITION ON GROWTH AND CHLAMYDOSPORE FORMATION IN BROWN AND GRAY CULTURES OF THIELAVIOPSIS BASICOLA

Physiological differences between brown and gray wild type cultures of Thielaviopsis basicola were sought in order to develop selective media for use in mutational studies, and as a basis for pathogenicity and ecological studies. The gray wild type was more thiamine-deficient, yielded less mycelium, and grew more slowly than the brown on all media tested regardless of composition and thiamine content. In liquid media both types were more thiamine-deficient on sucrose than on glucose, but the reverse was true on agar media. The gray type was inhibited more than the brown by malachite and methyl green. A two-layered thiamine-deficient agar medium, and one containing dyes, was selective for the brown type. Gray and brown types grew better on thiamine-deficient water agar and soil extract agar than on thiamine-deficient agar media containing 20 gm/l. of sugar and 1 gm./l. of nitrogen compounds. On thiamine-deficient media, distortion and extrusion of the contents of endoconidia and hyphae were more common with the gray wild type than the brown.Endoconidia, but not chlamydospores, were formed in varying amounts on all thiamine-deficient media. The addition of thiamine resulted in the abundant production of chlamydospores and greatly increased growth. Chlamydospore production was also influenced by the source of nitrogen. Certain amino acids were more inhibitory to chlamydospore formation by the brown than gray type and vice versa. Asparagine, for example, blocked chlamydospore formation by the brown but not the gray type, even though growth and endoconidial production were abundant. Mutants capable of overcoming this blockage were readily produced in culture.