HOMOTHALLISM AND HETEROTHALLISM IN SORDARIA-BREVICOLLIS

Sordaria brevicollis is a filamentous ascomycete previously considered to be exclusively heterothallic. Here we show that S. brevicollis can exhibit homothallism, and describe the genetic and environmental fact ors favouring the process. Both mating types can produce perithecia in unmated cultures, but only in the uncrossed perithecia of mtA are asc ospores formed (in < 30% of the fruitbodies). In most cases, only one or two asci are produced in any uncrossed mtA perithecium, although as many as 13 have been observed. The ascospores show no segregation for mating type; all are mtA. Heterokaryon analysis established that meio sis and recombination occurred during ascospore production in both hom othallic and heterothallic development. Homothallic fruiting is inhibi ted both by crossing with the opposite mating type, and by light.