Yu: Developing near-isogenic Brassica napus lines for differentiating pathotypes of Plasmodiophora brassicae
Date: February 2018
Term: 4 years
Status: Completed
Researcher(s): Fengqun Yu, Gary Peng, Bruce Gossen, Sally Vail, Agriculture and Agri-Food Canada, Saskatoon SK, Stephen Strelkov, University of Alberta, and Sheau-Fang Hwang, Alberta Agriculture and Rural Development
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: WGRF, ADF
Project Summary
Researchers initiated a four-year project in 2014 to develop a set of differential lines of spring type Brassica napus with single genes for identification of races of Plasmodiophora brassicae and for durable resistance to clubroot. Overall the project has resulted in two B. napus lines carrying Rcr1 and Rcr2 respectively and breeding lines carrying each of several other identified resistance genes, some of which have been distributed to canola seed companies. Canola breeders in the companies are incorporating the genes into their commercial cultivars for control of clubroot. Under a new project, more homozygous B. napus clubroot resistant lines from these materials are expected to be developed and clubroot pathogen races in western Canada to be determined.
Clubroot disease, caused by Plasmodiophora brassicae, poses a serious threat to canola production in western Canada. Several research groups have classified P. brassicae into various pathotypes based on differential reactions on Brassica cultivars. However, most of the differential cultivars used by the researchers are non-canola crops that belong to vegetable or fodder Brassicas. Ideally, a set of near-isogenic spring canola lines containing single clubroot resistance genes should be developed, and could be used for monitoring changes in the pathogen populations in canola fields.
Researchers with Agriculture and Agri-Food Canada in Saskatchewan and collaborators in Alberta, initiated a four-year project in 2014 to develop a set of differential lines of spring type B. napus with single genes for identification of races of P. brassicae and for durable resistance to clubroot. Additional objectives were to identify pathogen isolates and to validate DNA markers, which can be used to identify resistance genes in B. napus cultivars.
Previously, genetic mapping had identified 10 genes for clubroot resistance that occur in Brassica rapa, as well as in B. napus “Mendel”. Interspecific crosses and specific crosses were performed between canola line DH16516 and the respective B. rapa resistant donors containing Rcr1, Rcr2, Crr1 to Crr4, CRa, CRb, CRc and CRk and a B. napus cultivar containing clubroot resistance gene RcrM. Successive backcrosses were carried out using DH16516 as the recurrent parent. Molecular marker assisted selection was performed on each generation. Plants were tested with two Canadian pathotypes of P. brassicae (3 and 5X). B. napus lines containing Rcr1 or Rcr2 were successfully developed and are available to plant breeders. Plants containing the rest of CR genes in subsequent backcrosses were developed. Microspore culture is being performed for developing homozygous lines carrying the rest of the CR genes.
Researchers obtained a total of 33 strains of P. brassicae aggressive to Canadian resistant cultivars, 25 strains from University of Alberta, and four each from Bayer Crop Science and Crop Production Services. They are in the process of receiving more strains that can overcome the Canadian resistant cultivars from Alberta and strains collected from Saskatchewan. For this project, more than 1000 plants were tested for resistance to four stains of P. brassicae, pathotype 3, 5X-LG1, 5X-LG2 and 5X-LG3. Most of the donor lines were resistant to the four strains. It is likely that they carry more than one gene.
Analysis of SNP markers associated with CR genes in Brassica diploid species including B. rapa has been intensively carried out in the AAFC lab and used to validate SNP markers for this project. Up to date, SNP markers associated with Rcr1, Rcr2, CRa, CRb, CRk, RcrM and Crr3 on chromosome A03, Crr1 on A08, Crr2 on A01, and CRc on A02 were validated.
Overall the project has resulted in two B. napus lines carrying Rcr1 and Rcr2 respectively and breeding lines carrying each of several other identified resistance genes, some of which have been distributed to canola seed companies. Canola breeders in the companies are incorporating the genes into their commercial cultivars for control of clubroot. SNP markers linked to most of the clubroot resistance genes were validated. Under a new project, these materials and the continuation of performing backcrosses and marker assisted selection for B. napus lines containing each of single genes, will be obtained and races of the clubroot pathogen collected in western Canada in recent years will be determined.
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