Restriction Fragment Length Polymorphism Markers to Characterize Plasmodiophora brassicae Single-spore Isolates with Different Virulence Patterns

Plasmodiophora brassicae-speci®c clones were used to establish restriction fragment length polymorphism (RFLP) markers for four single-spore isolates of P. brassicae, which were originally selected from the ®eld isolate `eʹ and could be distinguished by infection tests with a small di€erential Arabidopsis thaliana set. The poor yield of DNA from the obligate biotrophic parasite was overcome by extracting DNA from young diseased roots of Brassica rapa. This mixture of host and parasite DNA was employed for RFLP and ®ngerprint studies utilizing selected P. brassicae-speci®c clones as hybridization probes