A NOVEL CLUBROOT RESISTANCE LOCUS IN Brassica rapa L.

¹ Faculty of Agriculture, Kyoto Prefectural University, Kita-Inayazuma, Seika, Kyoto, 619-0244 Japan

² National Institute of Vegetables and Tea Science (NIVTS), Ano, Mie 514-2392, Japan

³ Nagano Vegetable & Ornamental Crops Experiment Station, Matsushiro, Nagano 381-1211, Japan

⁴ Kyoto Prefectural Institute of Agricultural Biotechnology, Kita-Inayazuma, Seika, Kyoto, 619-0244, Japan

Clubroot disease caused by an obligate pathogen, Plasmodiophora brassicae, is a serious problem in Brassica crop production. To elucidate clubroot-resistance (CR) locus of CR turnip, "Milan White", an inbred CR turnip (Brassica rapa syn. campestris) line, N-WMR-3, was crossed with a clubroot-susceptible doubled haploid line, A9709. A segregating F3 population was obtained by single-seed descent of F2 plants and used for a genetic analysis. Disease incidence of the F3 population was scored using Ano-01 isolate as pathogen in a greenhouse at 30 C. Segregation of CR in the F3 population suggest that the CR is controlled by a major gene. Two RAPD markers were obtained as candidates of linkage markers by a bulked segregant analysis. They were then cloned and sequenced. The specific primer pairs amplified the polymorphic bands, and the bands were named OPC11-1S and OPC11-2S, respectively. The specific primer pair for OPC11-1S amplified a clear dominant band, while the primer pair for OPC11-2S resulted in co-dominant bands. Frequency distributions and statistical analyses indicate the presence of a major dominant CR gene linked to these two markers. The present markers for CR were independent of the previously found two CR loci, Crr1 andCrr2 (Suwabe et al. 2003). Genotypic distribution and statistical analyses did not show any evidence of CR alleles on Crr1 andCrr2 loci in N-WMR-3. The present study clearly demonstrates that Brassica rapa has at least three CR loci. Therefore, the new CR locus was named Crr3. The present locus may be useful in breeding CR Chinese cabbage cultivars.