Identificaiton of a clubroot resistance locus conferring resistance to a <i>Plasmodiophora brassicae</i> classified into pathotype group 3 in Chinese cabbage (<i>Brassica rapa</i> L.)

Abstract

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 F1 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 F2 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.

Fine mapping of the clubroot resistance gene <i>CRb</i> and development of a useful selectable marker in <i>Brassica rapa</i>

“…Although we mapped CRb between simple sequence repeat (SSR) markers KBrH059N21F and KBrH129J18R using the CR F 1 cultivar ‘Akiriso’ and ‘CR Shinki’ (Kato et al 2012), there was a discrepancy between the results of Piao et al (2004) and ours in the position of marker TCR05 and the CRb locus. To resolve this discrepancy and develop useful markers closely linked to CRb , fine mapping of CRb is needed.…”

“…An F 2 population ( n = 2,032) obtained by selfing ‘CR Shinki’ was used for fine mapping analysis. To examine the positional relationship between CRa and CRb , we also used another 172 F 2 plants of ‘CR Shinki’ from our previous study (Kato et al 2012), the total number of F 2 plants used in combined analysis was 2,204.…”

“…We previously demonstrated that SSR markers, KBrH059N21F, KBrH129J18R and KBrB091M11R developed from bacterial artificial chromosome (BAC) end sequences in BrGSP were located around CRb (Kato et al 2012). We developed more SSR markers based on four full BAC sequences (KBrH059N21, KBrH129J18, KBrB091M11 and KBrH069E08).…”

“…We have identified Crr1 , Crr2 and Crr4 from CR turnip ‘Siloga’ (Suwabe et al 2003) and a line with Crr1 , Crr2 and Crr4 showed resistance to isolates of pathotype groups 1, 2 and 4, but not group 3 (unpublished). Recently, we demonstrated that CRb could confer resistance to an isolate in pathotype group 3 and could compensate for the race specificity of Crr1 and Crr2 (Kato et al 2012). CRb , which is derived from the European fodder turnip ‘Gelria R’ (Diederichsen et al 2009, Hirai 2006), was originally identified on B. rapa chromosome R3 through genetic analysis using a resistant doubled haploid line derived from B. rapa ‘CR Shinki’ (Piao et al 2004, 2009), and this locus functions as a strong dominant gene (Kato et al 2012).…”

“…Recently, we demonstrated that CRb could confer resistance to an isolate in pathotype group 3 and could compensate for the race specificity of Crr1 and Crr2 (Kato et al 2012). CRb , which is derived from the European fodder turnip ‘Gelria R’ (Diederichsen et al 2009, Hirai 2006), was originally identified on B. rapa chromosome R3 through genetic analysis using a resistant doubled haploid line derived from B. rapa ‘CR Shinki’ (Piao et al 2004, 2009), and this locus functions as a strong dominant gene (Kato et al 2012). CRa , CRc and CRk were examined using six isolates by Matsumoto et al (2012): CRa showed resistance to M85, which falls between groups 3 and 4, but CRc did not.…”