Mutation in Thanatephorus Cucumeris

Abstract

Fertile, homothallic, homokaryotic cultures selected from the progeny of two field isolates were used to study the occurrence and significance of mutants in Thanatephoru8 cucumeris (Frank) Donk. Mutations in the crucifer stem· attacking isolate occurred spontaneously and were also induced by ultraviolet irradiation. Six of the mutants showing stability in culture were compared with one another and with their parent culture. The mutants differed in cultural appearance, growth rate, general morphology, mean number of nuclei per cell, and pathogenicity to crucifer stems, but none could be induced to fruit. Comparison of their pathogenic reactions on radish stems suggests that a series of steps, each controlled by a different genetic factor, is involved in the invasion of stems by the fungus. In the other isolate, which was non.pathogenic, no mutants were detected.