Genetics and molecular mapping of resistance to Plasmodiophora brassicae pathotypes 2, 3, 5, 6, and 8 in rutabaga (Brassica napus var. napobrassica).

Clubroot disease, caused by Plasmodiophora brassicae, is a threat to the production of Brassica crops including oilseed B. napus. In Canada, several pathotypes of this pathogen, such as pathotypes 2, 3, 5, 6, and 8, were identified, and resistance to these pathotypes was found in a rutabaga (B. napus var. napobrassica) genotype. In this paper, we report the genetic basis and molecular mapping of this resistance by use of F ₂ , backcross (BC ₁ ), and doubled haploid (DH) populations generated from crossing of this rutabaga line to a susceptible spring B. napus canola line. The F ₁ , F ₂ , and BC ₁ populations were evaluated for resistance to pathotype 3, and the DH population was evaluated for resistance to pathotypes 2, 3, 5, 6, and 8. A 3:1 segregation in F ₂ and a 1:1 segregation in BC ₁ were found for resistance to pathotype 3, and a 1:1 segregation was found in the DH population for resistance to all pathotypes. Molecular mapping by using the DH population identified a genomic region on chromosome A8 carrying resistance to all five pathotypes. This suggests that a single gene or a cluster of genes, located in this genomic region, is involved in the control of resistance to these pathotypes.