Molecular Marker Analysis And Mapping Of Clubroot Resistance Genes In Brassica Rapa L.ssp.pekinensis

Chinese cabbage, which originated in China, is widely cultivated all around the country and isone of China’s most important vegetables. In recent years, clubroot disease in Chinese cabbage hasbeen developing fast and its infected area is ever-increasing. Now the disease has been found in allChinese cabbage main producing areas and it brings huge yield loss and quality deterioration toChinese cabbage production, thus it has become one of the most urgent diseases in China. Breeding ofresistant Chinese cabbage cultivars is the most effective approach to control the disease. The breedingprocedure could be accelerated by exploring tightly linked molecular markers to clubroot resistancegene and using marker-assisted selection.Five F₂populations were generated by self-pollination of5different F₁resistant hybrids. Bothfield and artificial inoculation tests were conducted to evaluate the resistance of five F₂populations.Based on BSA （Bulk Segregant Analysis） method and InDel techniques, several linked markers wereobtained and clubroot resistance genes were preliminary mapped. The detailed results are as follows:1. Five F₂populations were generated by self-pollination of5different F₁resistant hybrids. Fieldtests were conducted on population A00645-4and A00647-3, while artificial tests were conducted onthe other three populations, A10823-4, A10820-2and A00637-1. All the five populations showedphenotypic segregation and the segregation ratios all fitted to the3（resistant）:1（susceptible） ratio basedon the action of a single dominant allele. It indicated that the clubroot resistance in these materialsmight be mainly controlled by a single dominant gene, respectively.2. BSA method was used to screen molecular markers, thereby finding linked markers toclubroot resistance genes in population A00637-1, A00645-4and A10823-4. In population A00637-1,one STS marker and4InDel markers were found linked to the clubroot resistance gene, among whichthe nearest two are STS marker TCR05-R and InDel marker BrID90039with genetic distance of0.7cMand1.7cM, respectively. In population A00645-4,9InDel markers are found linked to the resistancegene. The flanking markers BrID90269and BrID11683closely linked to the resistance gene werelocated on each side, at genetic distances of2.0and2.5cM, respectively. In population A10823-4,five InDel markers were found linked to the resistance gene, which were also linked to the previouslocus in population A00645-4. The genetic distances of flanking markers to this locus were3.8cMand3.9cM, respectively.3. In F₂population A00645-4and A10823-4, the resistance genes were both mapped in aninterval of around1450kb on Scaffold10which is on chromosome A8of Brassica rapa.According to the genomic information of Brassica rapa and resistance gene annotation in thegenome,6resistance genes are predicted existing in a cluster in this interval. In populationA00637-1, the resistance gene was mapped on chromosome A3of Brassica rapa, nearby Scaffold13in detail. The InDel makers which are tightly linked to clubroot resistance gene obtained in this researchcould be used for marker-assisted selection in the breeding of clubroot-resistant Chinese cabbage.Meanwhile, the results also lay the foundation for fine mapping and clone of clubroot resistance genes.