SYSTEMATICS OF THE ASCOMYCETOUS YEASTS ASSESSED FROM RIBOSOMAL-RNA SEQUENCE DIVERGENCE

Extent of divergence in partial nucleotide sequences from large and small subunit ribosomal RNAs was used to estimate genetic relationships among ascomycetous yeasts and yeastlike fungi. The comparisons showed four phylogenetically distinct groups comprised of the following taxa: Group 1. The budding yeasts Saccharomyces, Saccharomycopsis, Debaryomyces, Metschnikowia, Saturnospora, and Lipomyces, and the yeastlike genera Ascoidea, Cephaloascus, Dipodascus, Dipodascopsis, and Galactomyces; Group 2. Eremascus, Emericella and Ceratocystis; Group 3. Taphrina and Protomyces; Group 4. Schizosaccharomyces. Because of the genetic relationships indicated by sequence analysis, Group 1 taxa are retained in the order Endomycetales, and Schizosaccharomyces is retained in the Schizosaccharomycetales Prillinger et al. ex Kurtzman.