Analysis of ribosomal DNA sequences of Polymyxa species and related fungi and the development of genus- and species-specific PCR primers

A region of about 800 bp of ribosomal DNA has been sequenced in 10 isolates of Polymyxa and one isolate each of Plasmodiophora brassicae and the chytrid Olpidium brassicae. This region consists of about 330 bp at the 3' end of the 18S gene, the 5.8S DNA and the two internal transcribed spacers. A shorter region was also sequenced from one isolate each of Spongospora subterranea and a Ligniera sp. The results supported the earlier division of P. graminis into three subgroups and the recognition of P. betae as a distinct species. In phylogenetic analyses, the Ligniera and Spongospora isolates grouped with the other plasmodiophorids and the Olpidium isolate with the Mycota. The plasmodiophorids appeared as a distinct group and were not closely related to any other eukaryotes (including a range of fungi and protozoa). The DNA sequences were used to design primers for specific amplification of either Polymyxa or P. graminis DNA.