A contribution to the species definition in the genus Exobasidium (Basidiomycetes)

The G + C content of the DNA from 25 strains of various species of the parasitic Exobasidia (Basidiomycetes) ranges from 39.1 to 68.1 mol%. They can be ordered into ten distinct groups. Exobasidium vaccinii (65.8-68.1 mol% G + C) lives on various Vaccinium species causing mostly local infections. E. splendidum (48.0-51.7 mol% G + C) was found on the same Vaccinium species and also on Arctostaphylos uva-ursi. E. vaccinii-uliginosi (43.7-47.7 mol% G + C) found on Vaccinium uliginosum did not fit into any other group and therefore represents a distinct species. Systemic infections on both Vaccinium myrtillus and V. vitis-idaea are caused by E. myrtilli (39.1-39.9 mol% G + C). On Rhododendron species two different groups of Exobasidia have been found with G 4- C mol% of about 47.5 and 55.8. E. japonicum on Azalea indica is characterized by 40.3 mol% G + C, which could not be found in other Exobasidia attacking Rhododendron species. From Andromeda polifolia two Exobasidia with different G + C contents (43.7 and 52.8 mol% G + C) could be isolated. The G + C content in E. vexans, which parasitizes on members of the Theaceae, is 53.2 mol%. The wide range of G 4- C values in Exobasidium, very unusual within one genus, renders the G + C content of DNA a very useful tool for taxonomic studies.