Genetic Evidence for Hybridization in an Interspecific Cross in the Genus Sordaria

Abstract

SUMMARY: When the two heterothallic species Sordaria heterothallis and S. thermophila are crossed, two types of viable ascospores are recovered. The first, the mature black ascospore, is produced with a mature eight-spored ascus formed from an intraspecific fusion of nuclei of the same mating type. The second, the non-pigmented germinable ascospore, is produced by the interspecific fusion of nuclei of opposite mating types within an ascus in which all other ascospores are aborted. The non-pigmented ascospore is the product of the mixed genomes of the two species. It is a recombinant spore from which either species may be obtained by the partial substitution of its genome through successive backcrosses. Its inability to develop pigmentation, the irregular growth patterns of some of the strains which it produces and their inability to react in complementation tests, appear to be the result of a lack of affinity between the two species.