Characterization of a Single-Spore Isolate Population of Plasmodiophora brassicae Resulting from a Single Club

The single-spore isolates e3 and e6 of Plasmodiophora brassicae with different virulence patterns were distinguished by restriction fragment length polymorphisms in fingerprint-like patterns and by electrophoretic karyotypes using repetitive fragments as hybridization probes. These molecular tools were used to characterize a set of isolates originated from an infected root, which was inoculated with a mixture of the two singlespore isolates (e3 and e6). Spores harvested from mixed-infected roots were used to establish 53 new single- spore isolates. All these single-spore isolates revealed parental patterns according to their molecular fingerprints and their virulence pattern. No sexual recombination could be detected with repetitive molecular probes. However, one isolate (M36ES49) showed the same fingerprint pattern and virulence pattern but different sizes of small chromosomes than the parental type e6 , which is taken as an indication of chromosome rearrangement during the infection cycle