COCHLIOBOLUS SATIVUS: IV. DRUG-RESISTANT, COLOR, AND NUTRITIONALLY EXACTING MUTANTS

Auxotrophic mutants of Cochliobolus sativus were obtained from survivors of ultraviolet radiation by a modified total-isolation technique. Five or six hyphal tip isolations made from each survivor were tested for nutritional deficiencies. Although 0.48% of the survivors yielded auxotrophs, only about one-third of the hyphal tip isolations from these survivors were auxotrophic. Apparently, mutation in a multinucleate propagule resulted in a heterokaryotic culture and only some of the isolations from a culture were homokaryotic for the mutation. Some of the mutants were morphologically distinct from their parent and one, a methionineless strain, had white spores. Results indicated that recurrent requirements for growth occurred at different mutational sites.A strain resistant to the antibiotic anisomycin appeared as a spontaneous mutation. This strain grew at 1500 and its spores germinated at 1750 p.p.m.; wild-type isolates grew only at 75 and their spores germinated at 100 p.p.m. of the drug. The resistant mutant was pathogenic to wheat seedlings.