Compatibility and Population Studies of Three Species of Tremella

Three species of Tremella are examined to document their mating compatibility system, confirm their identity as biological species, and define their population structures in terms of mating type allele frequency and distribution. Confirmation of intersterility was made by pairing A1 and A2 isolates of each of the three presumptive species in all possible combinations. No detectable reaction could be observed when interspecific haploid yeast cells were paired; all isolates intermingled but remained in a budding yeast phase. Isolates of the same species produced either clamped, dikaryotic mycelium or conjugation tubes whenever pairings involved unlike A alleles. Allele frequencies at the B locus were determined from sample populations for each species. Alleles were recovered in statistically equal frequencies from T. globospora and T. indecorata, but significant departure from uniform allele frequency was observed in T. moriformis.T. moriformis was isolated from ornamental tree species in Davis, California, and was not found outside the city. B allele diversity is significantly lower in this species than in other species of the genus. Due to the low allele diversity, an introduction of the fungus to the Davis area may have contained most of the alleles of the parental population. B allele frequency is not uniform and selective pressures over and above those associated with self-incompatibility may be responsible for this observed non-uniformity.