Objective  Pathogenicity of various strains of Plasmodiophora brassicae on Brassica napus cultivars was investigated.

  Method  Four different P. brassicaes strains were collected from the counties of Xixiang, Nanzheng, Mian, and Taibai in Shaanxi, and the disease-resistance of 15 varieties of B. napus toward them by inoculating in the roots determined in an indoor test.

  Result  The pathogenicity of the various strains were significantly different.The P. brassicaes collected from Mian county was the strongest among all, while from Nanzheng county the weakest. The disease-resistance of the 15 rapeseed varieties differed significantly as well. The 5 significantly more resistant varieties, 62R, Huashuang 5R, 1628A×genkang, 171R, and 172R, were not native Shaanxi cultivars. The cluster analysis classified them as disease-resistant toward the clubroot disease and the 10 local germplasms disease-sensitive.

  Conclusion  Physiological differences existed among the strains of P. brassicaes from the 4 regions in Shaanxi. The 5 identified clubroot disease-resistant rapeseed cultivars would be promising candidates for breeding new varieties for cultivation in the province.