Identification of three novel QTL for resistance to highly aggressive Canadian strains of Plasmodiophora brassicae in rutabaga cultivar ECD10

<i>Plasmodiophora brassicae</i>, the causal pathogen of clubroot, has emerged as a significant threat to the production of Canada's most important oilseed crop canola. The <i>B. napus</i> rutabaga cultivar 'Wilhelmsburger' (ECD10) has shown a high resistance level to Canadian <i>P. brassicae</i> strains. This study utilized genotyping-by-sequencing (GBS) to identify single-nucleotide polymorphism (SNP) markers for mapping QTL related to resistance to 11 P<i>. brassicae</i> strains in a BC₁/BC₁S₁ population. The short reads from the GBS were assembled to the Chinese canola cultivar 'ZS11' reference genome. A genetic map spanning 1,812.6 cM was developed using 1,049 non-redundant SNPs identified from 92 BC₁ plants. Three quantitative trait loci (QTL) were identified: <i>Rcr13</i> on chromosome A02, <i>Rcr11</i> on A08, and <i>Rcr_C03-4^ECD10</i> on C03. <i>Rcr13</i> was related to resistance to four strains (2B, 8J, 5L, and 5X), explaining 14.2% to 81.7% of the phenotypic variation explained (PVE). <i>Rcr11</i> was associated with resistance to eight strains (3A, 2B, 5C, 3D, 8E, 5G, 3O, and 8P), explaining 20.2% to 83.2% of the PVE. <i>Rcr_C03-4^ECD10</i> was linked to resistance against strain 5C, explaining 21.5% of the PVE. Thirteen genes that encode proteins related to disease resistance were found as candidate genes for three QTL. The syntenic regions of the QTL were also examined with the reference genomes of the <i>B. rapa</i> `Chiifu', <i>B. oleracea</i> `D134' and eight different <i>Brassica napus</i> 'Darmor', `Gangan', `No2127', `Quinta', `Shengli', `Tapidor', `Westar', and `Zheyou7'. Differential reactions of the <i>B. napus</i> line carrying <i>Rcr11</i> or <i>Rcr13</i> with those carrying the previously identified CR genes <i>Rcr3</i> and <i>Rcr9</i> or <i>Rcr8</i> were found with the purified <i>P. brassicae</i> isolates. This is the first report of rutabaga-derived QTL effective against Canadian pathotypes that overcome 'Mendel' resistance.