Abstract
Clubroot disease cased by an obligate parasite, Plasmodiophora brassicae, is one of the most serious diseases of Brassica vegetables worldwide. A number of clubroot resistant (CR) Chinese cabbages (Brassica rapa) have been bred using European turnips as resistant sources. However, the breakdown of the resistance caused by variation in the pathogenicity of P.brassicae has been observed in various areas of Japan. Because inoculation test used for the classical breeding of the CR cultivars is time-consuming and laborious, DNA makers linked to two CR loci (Crr1 and Crr2) were developed. We demonstrated that the CR markers were useful for the selection of highly resistant plants from the backcrossed population. Nucleotide sequences of the CR markers showed homology to sequences of Arabidopsis chromosome 4, suggesting a synteny between Chinese cabbage and Arabidopsis. We could develop DNA markers tightly linked to the CR genes based on genomic information of Arabidopsis.
