SELF-FERTILITY AND UNIDIRECTIONAL MATING-TYPE SWITCHING IN CERATOCYSTIS-COERULESCENS, A FILAMENTOUS ASCOMYCETE

Individual perithecia from selfings of most Ceratocystis species produ ce both self-fertile and self-sterile progeny, apparently due to uni-d irectional mating-type switching. In C. coerulescens, male-only mutant s of otherwise hermaphroditic and self-fertile strains were self-steri le and were used in crossings to demonstrate that this species has two mating-types. Only MAT-2 strains are capable of selfing, and half of the progeny from a MAT-2 selfing are MAT-1. Male-only, MAT-2 mutants a re self-sterile and cross only with MAT-1 strains. Similarly, self-fer tile strains generally cross with only MAT-1 strains. MAT-1 strains on ly cross with MAT-2 strains and never self. It is hypothesized that th e switch in mating-type during selfing is associated with a deletion o f the MAT-2 gene.