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

Clubroot disease caused by the soil-borne pathogen Plasmodiophora brassicae Woronin is a major threat to the production of Brassica crops worldwide. The European winter canola cv. 'Mendel' shows resistance to many P. brassicae isolates including pathotypes 3, 5, 6 and 8 that are prevalent in Canada. To introgress clubroot resistance (CR) into Canadian spring Brassica napus canola, crosses between Canadian spring and European winter B. napus canola cv. 'Mendel' were made and several resistant lines were developed through pedigree breeding. Two of the resistant lines were further crossed with the clubroot susceptible spring canola line A07-26NR to produce two doubled haploid (DH) populations from nine F-1 plants. Segregation for resistance followed a 1:1 ratio for resistant and susceptible phenotypes suggesting that a single Mendelian gene is involved in the control of resistance to P. brassicae single spore isolate SACAN-ss1 (pathotype 3) in the DH population where the 'favourable allele' for resistance is derived from the cv. 'Mendel'. Genetic and physical mapping study positioned five previously described CR loci (CRk, Crr3, CRb, CRa and CRb (Kato) ) on the B. rapa chromosome A3, and identified twelve markers (1.5-2.0 % recombination) from the genomic region that houses the CRa and CRb (Kato) loci to be associated with the resistance derived from 'Mendel'. The identified markers can be used in breeding as well as pyramiding of multiple clubroot resistance genes.