SEQUENCES OF RIBOSOMAL GENES AND INTERNAL TRANSCRIBED SPACERS MOVE 3 PLANT-PARASITIC FUNGI, EREMOTHECIUM-ASHBYI, ASHBYA-GOSSYPII, AND NEMATOSPORA-CORYLI, TOWARDS SACCHAROMYCES-CEREVISIAE

Phylogenetic relationships between two species from the genera Sacchar omyces (S, cerevisiae, S. kluyveri) and Kluyveromyces (K. aestuarii, K . marxianus), a plant parasitic dimorphic yeast (Nematospora coryli), and two phytopathogenic filamentous fungi (Ashbya gossypii, Eremotheci um ashbyi) were investigated by comparing partial nucleotide sequences of ribosomal DNA (rDNA). The three types of sequenced regions evolve with different speed and allow the analysis at distinct taxonomic leve ls: conserved regions (18S rDNA, small ribosomal subunit), variable re gions (25S rDNA, large ribosomal subunit), and highly variable regions ITS1 and ITS2 (internal transcribed spacers). Segments homologous to positions 619 to 1035 and 1205 to 1617 of the 18S rDNA and positions 4 70 to 890 and 1535 to 1984 of the 25S rDNA of S. cerevisiae were seque nced. The maximal resolving power of rDNA sequence analysis is provide d by including the rapidly evolving ITS1 and ITS2 regions. In the phyl ogenetic sequence analysis of all regions by the genera Kluyveromyces and Saccharomyces cluster together with two filamentous pathogens on c otton, A. gossypii and E. ashby, as well as the plant pathogenic yeast N. coryli. The molecular evidence from ribosomal sequences suggests t hat morphology and ornamentation of ascospores, the persistence of asc us walls as well as mycelium formation should not be used as different iating characters in yeast taxonomy, especially in family delimitation . Our sequence data support the inclusion of plant pathogenic, predomi nantly filamentous genera like Ashbya or Eremothecium or dimorphic gen era like Nematospora with falcate ascospores within a new family of th e Saccharomycetaceae. Similarly, the saprophytic genus Kluyveromyces w ith reniform ascospores and deliquescent ascus walls unequivocally bel ongs to the family of Saccharomycetaceae.