Race-specific reaction of resistance to black rot in Brassica oleracea

Several black rot-resistant varieties of Brassica oleracea showed a race-specific hypersensitive response (HR) to inoculation with Xanthomonas campestris pv. campestris isolates of different races. In progenies of cabbage line PI436606, Portuguese kale ISA454 and Chinese kale SR1 the HR to race 1 of the pathogen was controlled by a dominant gene named R1, when a recessive gene r5 was responsible for the HR to race 5. Genes with a similar race-specific reaction were assumed on the basis of gene-for-gene interaction in black rot-resistant Japanese cabbage cultivars and double haploid lines obtained from them. Homology of gene r5 in cabbage lines PI436606, Fujiwase 01 and kale ISA454 was postulated in crosses between those lines or their progenies. In a cross between SR1 and PI436606, interaction between resistance to race 1 and non-specific resistance localized in the stem vascular system was found. On the basis of pedigree information and homology of resistance genes in the cultivars of East-Asian cabbage and Portuguese kales, the probable origin of race-specific resistance to black rot of cole crops was suggested to be in heading Mediterranean kale. Some evidence was found for a gene conferring resistance to race 4 in B. oleracea.