Peculiarities of hybrid formation and copulation activity in the yeast Pachysolen tannophilus

The copulation activity and hybrid formation efficiency have been studied in the xylose-assimilating yeast Pachysolen tannophilus. It was shown that the presence of 2% D-glucose, 0.5% yeast extract, and 2% agarose in the growth medium provided for the highest frequencies of hybrid formation. Atypical hybrid cultures similar in morphophysiological characteristics to native haploid strains of P. tannophilus were revealed in the course of hybridization. The genesis mechanism of such culture and the reasons for the restricted applicability of hybridological analysis to genetic studies of P. tannophilus are discussed.