The susceptibility of Brassica oleracea cultivars to Plasmodiophora brassicae (clubroot)

An evaluation of 404 Brassica oleracea cultivars for susceptibility to Plasmodiophora brassicae (clubroot) at one field site in northern Scotland over the four years 1979-82 is reported. The population of P. brassicae at this site possessed a high degree of virulence to B. oleracea as determined by seedling tests in a glasshouse environment, using the European Clubroot Differential series. No statistically significant differences in susceptibility were consistently identified between cultivars when tested under field conditions. Data over years and over crops were analysed by the residual maximum likelihood technique. Differences between cultivars were small compared with cultivar x year interactions. No obvious differences were identified in susceptibility between the crop types Brussels sprout, cabbage, calabrese and cauliflower. Disease levels as analysed over all field trials increased markedly in years three and four of this experiment compared with the first two years.