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

Abstract

In Chinese cabbage (Brassica rapa), the clubroot resistance (CR) gene CRb is effective against Plasmodiophora brassicae isolate No. 14, which is classified as pathotype group 3. Although markers linked to CRb have been reported, an accurate position in the genome and the gene structure are unknown. To determine the genomic location and estimate the structure of CRb, we developed 28 markers (average distance, 20.4 kb) around CRb and constructed a high-density partial map. The precise position of CRb was determined by using a population of 2,032 F2 plants generated by selfing B. rapa ‘CR Shinki.’ We determined that CRb is located in the 140-kb genomic region between markers KB59N07 and B1005 and found candidate resistance genes. Among other CR genes on chromosome R3, a genotype of CRa closest marker clearly matched those of CRb and Crr3 did not confer resistance to isolate No. 14. Based on the genotypes of 11 markers developed near CRb and resistance to isolate No. 14, 82 of 108 cultivars showed a strong correlation between genotypes and phenotypes. The results of this study will be useful for isolating CRb and breeding cultivars with resistance to pathotype group 3 by introducing CRb into susceptible cultivars through marker-assisted selection.

Mapping of the clubroot disease resistance in spring Brassica napus canola introgressed from European winter canola cv. ‘Mendel’

“…2. Also, linkage analysis integrated 11 markers reported by Kato et al (2013) which co-segregated with the resistance derived from 'Mendel' with the one co-segregating marker reported by Ueno et al (2012). Thus, all 12 co-segregating markers mapped to the A3 chromosome (Fig.…”

“…The genomic DNA of the parents and the bulks were screened with 370 (212 A ? 158 C) Brassica SSR markers obtained from Agriculture and AgriFood Canada (AAFC) through a material transfer agreement, one RAPD marker (Diederichsen et al 2006), two SSR markers flanking the CR locus of A3 and two markers from C3 linkage groups of Werner et al (2008), and 72 published markers reported to be linked to the nine published CR loci: the CRa (Matsumoto et al 1998Hayashida et al 2008;Ueno et al 2012), CRb (Piao et al 2004, Zhang et al 2014, CRb Kato (Kato et al 2012(Kato et al , 2013, CRk and Crr3 (Hirai et al 2004;Saito et al 2006) on A3, CRc on A2 Matsumoto et al 2012), Crr1, Crr2 and Crr4 on A8, A1 and A6, respectively (Suwabe et al 2003. For convenience of reference to the molecular markers and discussion, the locus reported by Kato et al (2012Kato et al ( , 2013 will be referred hereafter as CRb Kato .…”

“…In the case of the 37 DNA markers reported to be linked to the CRb Kato locus (Kato et al 2012(Kato et al , 2013 and screened by bulk segregant analysis, 15 markers detected polymorphism between the parents, 17 gave monomorphic bands while five failed to amplify the genomic DNA. About a quarter (26.7 %) of the polymorphic markers (KBrH129J08R, KB69N08, KB69N07 and KBrH059N21F) tested on the 200 lines of the two DH populations were not strongly associated with clubroot resistance; recombination frequency was in the range of 9.0-24.5 %.…”

“…Therefore, these donor sources have been used in many breeding programs to develop clubroot resistant cultivars of B. napus rutabaga (Gowers 1982;Bradshaw et al 1997) and winter canola (Diederichsen and Sacristán 1996;Frauen 1999). To date five major loci, viz., CRk , Crr3 (Hirai et al 2004;Saito et al 2006), CRb (Piao et al 2004;Zhang et al 2014), CRa (Matsumoto et al 1998Hayashida et al 2008;Ueno et al 2012) and CRb Kato (Kato et al 2012(Kato et al , 2013 conferring resistance to clubroot disease have been mapped onto the A3 chromosome of B. rapa. Additional four clubroot resistance loci were mapped to four other chromosomes, such as, CRc to the chromosome A2 Matsumoto et al 2012), Crr1 to A8, Crr2 to A1, and Crr4 to A6 (Suwabe et al 2003 (Rahman et al 2011).…”

Genome resequencing and comparative variome analysis in a Brassica rapa and Brassica oleracea collection

“…Further studies reported the phenomenon of sub-genome dominance among the three sub-genomes in Brassica s 8,9 , and found that the biased distribution of small RNA-targeted TEs plays an important role in this phenomenon 11,12 . Furthermore, the release of the genome sequences has also contributed to the mapping, cloning and functional studies of agronomic genes in Brassica crops, such as two clubroot resistance genes 13,14 , two blackleg resistance genes 15,16 , as well as two key genes regulating the time of flowering 17–19 . The availability of these reference genomes also made it possible to build variome datasets by resequencing populations of B. rapa and B. oleracea , to investigate domestication of the diverse morphotypes.…”