Characterisation of Polymyxa species by restriction analysis of PCR-amplified ribosomal DNA

A molecular method is described to aid identification of the obligate parasite Polymyxa and discriminate between species (P. betae and P. graminis) and isolates. DNA was extracted from zoospores, resting spores and roots infected with P. betae and P. graminis and compared with that from negative control plants that were not inoculated with Polymyxa but were grown at the same time under the same conditions. The ribosomal internal transcribed spacers and 5.8S rDNAs were amplified by the polymerase chain reaction and digested with restriction enzymes to detect molecular differences between the species and isolates. There were differences between P. betae and P. graminis and two subgroups within P. graminis but so far this has not been correlated with any other biological property.