Clubroot Pathotype Evaluation and Monitoring

Term: 3 years, beginning 2024
Status: Ongoing
Researcher(s): Stephen Strelkov, U of A
SaskCanola Investment: $90,562.50
Total Project Cost: $362,250
Funding Partners: WGRF, ACPC

Objective

1. Tracking clubroot occurrence, severity and spread. 

2. Generation of P. brassicae field isolates from infected roots. 

3. Monitoring pathotype composition and virulence shifts, including identification of resistance-breaking pathotypes and their prevalence. 

4. Providing recommendations to the Clubroot Steering Committee and other stakeholders regarding pathotypes of particular concern and emerging issue 

Project Description

Since 2013, clubroot has been diagnosed in at least 3,894 individual fields across Alberta, with dozens of cases also reported in Saskatchewan and Manitoba. The management of clubroot is challenging, as P. brassicae produces large numbers of long-lived resting spores that can cause severe yield losses in susceptible hosts. Genetic resistance is the most effective tool for disease control, but the emergence of new pathotypes that can ‘break’ or overcome host resistance indicates that this tool is at serious risk. Forty-three pathotypes of P. brassicae have now been identified in Canada, 25 of which are virulent on at least some clubroot-resistant canola varieties. Rapid shifts in the virulence of the pathogen, combined with the continued emergence and spread of resistance-breaking pathotypes, indicate a need for proactive disease management and resistance-breeding efforts. 

To be effective, such efforts must be based on up-to-date knowledge of the occurrence, spread and pathotype composition of western Canadian P. brassicae populations. This knowledge is particularly important given the rapid shifts that have been observed with respect to clubroot pathotype composition over the past decade. Prior to the release of the first clubroot-resistant canola varieties, pathotype 3H (as it is now known) was predominant in most P. brassicae-infested fields. However, within a few years of the introduction of the resistance trait, 3H had largely been replaced by the ‘resistance-breaking’ pathotypes 3A and 3D. Consequently, breeders and companies had to develop canola hybrids carrying novel sources of resistance that could control these pathotypes, which in turn may be driving further diversification in pathogen virulence. Indeed, the emergence of other pathotypes such as the resistance-breaking 9E underscores the need for continued clubroot surveillance. This surveillance includes not only the tracking of disease occurrence, severity and spread, but also generation of P. brassicae collections for pathotype identification and detection of virulence shifts, as well as practical recommendations regarding the trends and pathotypes of greatest concern. This project will allow these activities to continue and provide the information and pathogen material necessary for effective resistance breeding and clubroot management in the coming years.