STUDIES IN HETEROBASIDIOMYCETES .36. A COMPARISON OF 5S RIBOSOMAL-RNA NUCLEOTIDE-SEQUENCES FROM SMUT FUNGI

The 5S rRNA nucleotide sequences from 7 smut fungi, Ustilago hordei, U. longissima, U. maydis, U. scabiosae, Farysia thuemenii, Ginanniella primulicola and Sphacelotheca spp., as well as from Rhodosporidium malvinellum were determined and compared with sequences from other basidiomycetous fungi. The 5S rRNA nucleotide sequences of these fungi show striking differences, indicating that the smut fungi are not a coherent group. Smuts parasitizing members of the Caryophyllaceae, Dipsacaceae and Polygonaceae fit with cluster 1 of Walker and Doolittle''s classification of basidiomycetous 5S rRNAs, while U. hordei, U. longissima and G. primulicola are more closely related to Tilletia controversa and other fungi of their cluster 3. U. maydis and F. thuemenii represent 2 new clusters, each near the U. hordei group. The 5S rRNA from R. mvalvinellum differs so much from that of R. toruloides that it does not fit the same cluster. Those smut fungi of our study, which parasitize dicots, cannot be kept in the order Ustilaginales any longer, but will have to be placed together with R. toruloides in a separate group. Taxonomic consequences should not be based on a single characteristic; they will be discussed in a comprehensive, separate study.