Six pathogenic races of Plasmodiophora brassicae Wor. in New Zealand

In addition to the pathogenic races A and B described previously, four more races of Plasmodiophora brassicae Wor., designated C, D, E, and F, have been identified. Races C and D, together with race B, were isolated from one collection of N.Z. Clubroot Resistant rape ( Brassica napus L. ssp. rapifera (Metzg.) Sinsk.) grown at Lincoln after sub‐culturing on three differential hosts. Race C severely infected N.Z. Wilhelmsburger swede ( Brassica napus L. ssp. rapifera (Metzg.) Sinsk.), but not Clubroot Resistant rape or N.Z. Purple Resistant turnip ( Brassica campestris L. ssp. rapifera (Metzg.) Sinsk.). Race D severely infected Purple Resistant turnip, but not Clubroot Resistant rape or Wilhelmsburger swede. Race E was isolated from Clubroot Resistant rape grown at Winton. It severely infected both Clubroot Resistant rape and Wilhelmsburger swede and moderately infected Purple Resistant turnip. Race F was isolated from N.Z. Broad‐leaf Essex rape grown at Ohakune. It severely infected Giant Chou Moellier ( Brassica oleracea L. ssp. acephala .). There was no evidence of synergism or antagonism between races B, C, and D. Race E was the only race that caused a high level of infection on N.Z. Wye swede in two out of three experiments.