The phylogenetic relationships of the Q9-equipped, hat-shaped ascospore-forming species of the genus Yamadazyma Billon-Grand (Saccharomycetaceae) based on the partial sequences of 18S and 26S ribosomal RNAs.

Sixteen strains of the sixteen species, including the type species, Y. philogaea (CBS 6696, type strain), of the genus Yamadazyma were examined for their partial base sequences of 18S and 26S rRNAs. The genus Yamadazyma Billon-Grand was found to have a heterogeneous nature phylogenetically. In the partial base sequences in positions 1451-1618 (168 bases) of 18S rRNA, the number of base differences was 4-0 within the genus except for Y. spartinae, Y. inositovora, Y. ohmeri, and Y. besseyi. The base differences numbered 6-1, 11-8, and 8-4 with D. hansenii, P. membranaefaciens, and S. cerevisiae, respectively. In the partial base sequences in positions 1611-1835 (225 bases) of 26S rRNA, the number of base differences was 14-0 within the genus. The base differences numbered 19-0, 31-24, and 25-17 with D. hansenii, P. membranaefaciens, and S. cerevisiae, respectively. In the partial base sequences in positions 493-622 (130 bases) of 26S rRNA, the percent similarities were 73-93. The percent similarities were 77-90, 64-71, and 68-79 with D. hansenii, P. membranaefaciens, and S. cerevisiae, respectively. Yamadazyma inositovora, Y. spartinae, and Y. ohmeri were not closely related phylogenetically. Yamadazyma besseyi (Q-7) was separate phylogenetically from the species mentioned above of the genera Yamadazyma, Debaryomyces, Pichia, and Saccharomyces (base differences, 13-7 and 62-17; percent similarities, 48-63). The discussion was made phylogenetically and taxonomically, especially on transferring Y. besseyi to a separate taxon.