Comparison of resistance of cauliflower and kohlrabi to clubroot

Obligate biotroph soil borne pathogen Plasmodiophora brassicae Wor. causing clubroot disease is one of the most serious diseases of cruciferous crops worldwide. Cauliflower and kohlrabi are important and favourite Brassica vegetables for consumers. The growing in a soil infested by P. brassicae leads to economically significant loses in yield. The most effective production is to grow resistant cultivars. In this experiment, 7,079 plants of 50 cultivars of cauliflower (Brassica oleracea L. var. botrytis L.) and 4,486 plants of 30 cultivars of kohlrabi (Brassica oleracea L. var. gongylodes L.) from a germplasm collection maintained by Crop Research Institute in Olomouc, Czech Republic, were tested for resistance to clubroot disease under controlled conditions of plant growth chamber. Tolerance of these two crops was compared and statistically evaluated by PCA and parallel coordinate plot. Kohlrabi showed higher tolerance by average disease index (DI) 73.07. Average DI of cauliflower was 77.21. Kohlrabi showed a higher average percentage of resistant plants with no visible swelling or very light swelling (22.86%) than cauliflower (16.33%). The obtained results can be used by breeders as initial sources of resistance to clubroot.