Indentification of New Clubroot Resistant Locus in Chinese Cabbage (Brassica rapa L.) Against Plasmodiophora brassicae Pathotypes of Korea

Clubroot disease, which is caused by the soil-borne plant pathogen Plasmodiophora brassicae Woronin, is the most serious disease in cultivated Brassica species such as Brassica rapa, B. oleracea and B. napus. P. brassicae causes abnormal cell enlargement and cell division of infected roots that produces characteristic deforming galls. Thus this disease causes substantial reductions in crop quality and yield. Many mapping studies for CR loci have been reported in Brassica to date, and at least eight CR loci such as Crr1, Crr2, Crr3, Crr4, CRa, CRb, CRc, and CRk have been identified in B. rapa. In Japan, four pathotypic groups (group 1 to group 4) were identified from the collected field isolates. Recently, a B. rapa cultivar named ‘Akimeki’ has been developed which is resistant against all four pathotype groups. In Korean field, very similar pathotypic groups against each of the four Japanese pathotypes have been identified. The four Korean pathotypes are: wild type, mutant type 1, mutant type 2 and mutant type 3. The Japanese cultivar ‘Akimeki’ showed resistance against wild type, mutant type 1 and mutant type 2 pathotypes of Korea. But notably the ‘Akimeki’ cultivar was found susceptible against the mutant type 3. The results indicated that the pathotype mutant groups between Japan and Korea differ in CR locus. We believe that the CR locus present in Korean mutant type 3 might be a new locus that has not been reported before. Therefore we have planned to map the probable unknown locus present mutant type 3. To achieve this objective we have crossed resistant and susceptible lines of mutant type 3, produced F₁ generation and subsequently the F₂ generation. The F₂ generation is being sequenced by RAD-seq. and the data to be used to construct a genetic map of the predicted new locus present in mutant type 3. (213003-04-3-SB110, 213003-04-3-SB420)