The Genetics of Sexual Incompatibility in the Indian Paint Fungus, Echinodontium Tinctorium
Basidiocarps of Echinodontium tinctorium were collected from three widely separated localities in Idaho and Arizona. Freezing basidiospore prints at -20 C for ten weeks stimulated germination. The role of low temperatures in breaking spore dormancy is discussed relative to environmental adaptation. Single-spore isolates of a single basidiocarp from each location were paired separately in all possible combinations. Four mating types were identified from each basidiocarp in Idaho. Four types of macroscopic interactions were observed in pairings between sympatric isolates. Basidiospores and cells of hyphae derived from basidiospores were monokaryotic (uninucleate), lacked clamp connections, and appeared haploid. Heterokaryotic hyphae derived from compatible matings were dikaryotic, exhibited clamp connections, and resembled generative contextual hyphae of basidiocarps. Complete intercompatibility between allopatric isolates demonstrated that the incompatibility factors were multiallelic. The fungus apparently does not fruit in culture, although mating results and cytological data indicate that it is heterothallic with a bifactorial (tetrapolar) mating system in which sexual incompatibility is controlled by multiple alleles at two loci on separate chromosomes.