Buchwaldt: Development of Sclerotinia Resistant Brassica Napus Lines and Molecular Markers for Marker-Assisted Breeding

Date: April 2013
Term: 3 years
Status: Completed
Researcher(s): Dwayne Hegedus, Lone Buchwaldt and Isobel Parkin, Agriculture and Agri-Food Canada, Saskatoon
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a

Project Summary

Sclerotinia stem rot is one of the major diseases affecting canola production. New varieties of Brassica napus canola with improved levels of sclerotinia resistance are required as part of an integrated management strategy. A breakthrough in sclerotinia resistance screening has enabled researchers at Agriculture and Agri-Food Canada to identify new resistant germplasm, develop molecular markers and identify additional B. napus defense genes. The project results will help researchers generate the genetic information and breeding tools needed for successful development of sclerotinia resistant cultivars.

Sclerotinia stem rot is one of the major diseases affecting canola production. Successful management of sclerotinia disease can be difficult to achieve given the lack of resistant crop cultivars, and limited impact of cultural practices on disease risk. New varieties of Brassica napus canola with improved levels of sclerotinia resistance are required as part of an integrated management strategy. A breakthrough in sclerotinia resistance screening has enabled identification of new resistant germplasm, development of molecular markers and identification of B. napus defense genes.

Researchers at Agriculture and Agri-Food Canada (AAFC) in Saskatoon, Saskatchewan initiated a three-year study in 2010 to identify new sources of sclerotinia stem rot resistance in B. napus accessions from the Plant Gene Resources Centre of Canada. They also wanted to identify molecular markers/genes associated with resistance that could be used for developing stem rot resistant canola varieties. This project has extended and built upon the resources and information developed through several previous research projects undertaken between 2005 and 2009.

Previous projects identified several sources of resistance among B. napus germplasm accessions from Pakistan, South Korea, Japan, China and a few countries in Europe. In the current project, several B. napus lines were genotyped with molecular markers. The results combined with sclerotinia severity data in an association analysis showed markers associated with resistance. The results also showed that lines from South Korea, Japan and some lines from China and Pakistan share similar resistance markers, while different markers were associated with resistance in European lines. The identification of more candidate defense genes and more precise genome mapping of sclerotinia resistance is underway.

Researchers also wanted to determine whether the newly identified B. napus lines would hold up against S. sclerotiorum isolates representative of the population in western Canada. New isolates were collected in a survey of 149 infected fields in 2010 across the three Prairie Provinces and characterized for their genomic relatedness and pathogenicity on selected resistant B. napus germplasm accessions. The survey revealed a high genetic variability determined by the molecular fingerprint of 127 isolates grouped into 17 sub-populations. One isolate representing each of the 17 sub-populations was selected for pathogenicity testing. Replicated trials of the 17 isolates on five partially resistant lines is in progress.

The simultaneous discovery of resistant B. napus lines, the availability of molecular markers, and high-through put genomics platforms is making the progress in the area of sclerotinia resistance breeding possible. Using marker-assisted breeding can achieve a higher level of resistance to stem rot in B. napus through combining these resistance genes in advanced breeding lines. Future research will utilize resistance in lines from South Korea, Japan and Pakistan and continue to clarify the function of single defence genes underlying the complex trait of sclerotinia resistance. The project results will help researchers generate the genetic information and breeding tools needed for successful development of sclerotinia resistant cultivars.

Figure 1. A Brassica napus line with high level of partial resistance to sclerotinia stem rot compared to a highly susceptible line. Plants were inoculating by attaching mycelium of the pathogen to the main stem. All germplasm lines and mapping populations were screened in a semi-field disease nursery at Agriculture and Agri-Food Canada’s research farm in Saskatoon. Source: Lone Buchwaldt, AAFC.

Scientific Publications

Gyawali S, Hegedus DD, Parkin IAP, Poon J, Higgins E, Horner K, Bekkaoui D, Coutu C and Buchwaldt L (2013) Genetic diversity and population structure in a world collection of Brassica napus accessions with emphasis on those from South Korea, Japan and Pakistan. Crop Science 53: 1537-1545.

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