Seed: Understanding clubroot resistance and the classification system

August 30, 2017 - Issue 23

Clubroot resistant (CR) canola varieties are key tools used to delay clubroot establishment and manage clubroot disease on the farm. However, to prevent rapid genetic shifts in clubroot populations and subsequent loss of effective resistance in CR varieties, this valuable resource must be used judiciously in an integrated management approach, which includes practicing a diverse crop rotation with at least two years between canola crops, effectively managing weeds, sanitizing equipment and minimizing soil movement.

Clubroot galls. Credit: Brittany Hennig


Resistance classifications

Clubroot resistance in a variety should be substantiated through standard testing procedures outlined in the Western Canada Canola/Rapeseed Recommending Committee (WCC/RRC) guidelines and protocols. Varieties are compared to the susceptible check variety for clubroot infection and are assigned either resistant (R), intermediate (I) or susceptible (S) ratings.

Clubroot pathotypes

A base resistance (R) label requires that the variety is resistant to the predominant clubroot strains or pathotypes in Western Canada. Additional ratings can be appended to the base ‘R’ label to describe resistance to specific uncommon or new pathotypes.

No CR varieties, including new ones with multiple resistance genes, are resistant to all of the clubroot pathotypes detected in Western Canada to date. As clubroot populations in infested fields become more diverse over time, and more CR resistance genes are bred into canola varieties, the usefulness of rotating CR varieties with different resistance will increase. Currently there are no tests commercially available for growers to distinguish or detect new virulent strains in their infested fields.

Careful scouting to detect early infestations to alert growers and deploy resistant varieties is of utmost importance. Waiting to use ‘R’ varieties until significant infestations have developed will create high soil spore loads and increase the probability for pathogen shifts which can rapidly defeat variety resistance.

Visit clubroot.ca to learn more. Scroll through the manage clubroot section to see a list of current clubroot resistant varieties.

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