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

Several black rot-resistant varieties of Brassica oleracea showed a race-sp ecific hypersensitive response (HR) to inoculation with Xanthomonas campest ris pv. campestris isolates of different races. In progenies of cabbage lin e 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-spe cific reaction were assumed on the basis of gene-for-gene interaction in bl ack rot-resistant Japanese cabbage cultivars and double haploid lines obtai ned from them. Homology of gene r5 in cabbage lines PI436606, Fujiwase 01 a nd kale ISA454 was postulated in crosses between those lines or their proge nies. In a cross between SR1 and PI436606, interaction between resistance t o 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 prob able origin of race-specific resistance to black rot of cole crops was sugg ested to be in heading Mediterranean kale. Some evidence was found for a ge ne conferring resistance to race 4 in B. oleracea.