TAXONOMIC RELATIONSHIPS IN THE GENUS EXOBASIDIUM (BASIDIOMYCETES) BASED ON RIBOSOMAL DNA ANALYSIS

Morphological criteria, host plant and type of infection are tradition ally used to differentiate species of the parasitic basidiomycetous ge nus Exobasidium, of which most species are restricted to host plants o f the Ericaceae. Strains isolated from host species of the genera Rhod odendron, Azalea and Vaccinium were investigated by DNA homology and R FLP analysis of the 26S rRNA gene in order to check host specificity a nd the traditionally used species concept in the genus. Part of the 26 S rRNA gene from 29 strains was amplified by polymerase chain reaction (PCR) and digested with five restriction enzymes. The results of DNA- DNA hybridization experiments and RFLP analysis correlate with data fr om DNA composition (molar content of guanine and cytosine). Strains as signed to one species by these data share an identical RFLP pattern. A ll Exobasidium species analysed are restricted to host species of a si ngle genus. Exobasidium vaccinii is found to parasitize at least three different species of Vaccinium. Within strains isolated from Rhododen dron ferrugineum and Rh, hirsutum at least two species can be distingu ished, both formerly regarded as Exobasidium rhododendri. Each of the other Exobasidium species investigated is restricted to one single hos t species, respectively.