Detection of plasmodiophora brassicae by PCR in naturally infested soils

A nested polymerase chain reaction (PCR) method was developed for detection of DNA from Plasmodiophora brassicae in naturally infested field soil samp les. The target sequences 389 bp and 507 bp were amplified from Swedish pop ulations of P. brassicae. The protocols described enabled detection of DNA in various soil classes with an inoculum level of P. brassicae correspondin g to a disease severity index (DSI) higher than 21 in a greenhouse bioassay . Three sequenced Swedish P. brassicae isolates had identical sequence in t he 18S/ITS 1 region, but differed by a few nucleotides from an isolate sequ enced in the UK. The results indicate that the primers used are general for P. brassicae, and consequently the nested PCR assay has a potential to be developed as a routine diagnostic test.