In Chinese cabbage (
Brassica rapa), the clubroot resistance (CR) genes
Crr1 and
Crr2 are effective against the mild
Plasmodiophora brassicae isolate Ano-01 and the more virulent isolate Wakayama-01, but not against isolate No. 14, classified into pathotype group 3. ‘Akiriso’, a clubroot-resistant F
1 cultivar, showed resistance to isolate No. 14. To increase the durability of resistance, we attempted to identify the CR locus in ‘Akiriso’. CR in ‘Akiriso’ segregated as a single dominant gene and was linked to several molecular markers that were also linked to
CRb, a CR locus from cultivar ‘CR Shinki’. We developed additional markers around
CRb and constructed partial genetic maps of this region in ‘Akiriso’ and ‘CR Shinki’. The positions and order of markers in the genetic maps of the two cultivars were very similar. The segregation ratios for resistance to isolate No. 14 in F
2 populations derived from each of the two cultivars were also very similar. These results suggest that the CR locus in ‘Akiriso’ is
CRb or a tightly linked locus. The newly developed markers in this study were more closely linked to
CRb than previously reported markers and will be useful for marker-assisted selection of
CRb in Chinese cabbage breeding.
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