Clubroot ‘race profiling’ can help boost resistance in canola

By Jeff Melchior

Racial profiling is not a term most people would want to be associated with. But with clubroot it’s different; it means the ability to select a canola variety that not only resists clubroot in general, but specific ″races″ of the disease of canola and other brassica plants.

AAFC researcher Fengqun Yu, right, and a research team member inspect an infected plant at Saskatoon’s research and development centre. Photo: AAFC

When it happens, thank an AAFC research team in Saskatoon that has developed canola breeding lines that are highly resistant to almost all known clubroot races in Canada.

″This could revolutionize the race differentiation for the clubroot pathogen,″ said an AAFC release.


″This is important because it will provide crop breeders and growers with information they can use when developing or growing cultivars with increased clubroot resistance.″

In the context of clubroot and other crop diseases, a ″race″ is a unique population in which all individuals carry the same combination of avirulent genes.

Profiling race structure in crop diseases isn’t new, said team leader Fengqun Yu. In fact it was developed 10 years ago to characterize the blackleg pathogen, another disease of canola.

Greenhouse-grown canola plant with two introduced clubroot resistance genes shows promise for the future, says researcher Fengqun Yu. photo: AAFC

″We are able to determine the race structure of the blackleg pathogen,″ said Yu. ″Our research wanted to catch up to the concept that’s widely used for blackleg.″

Basically, the researchers infect a canola gene to test its resistance to a given ″race″ of clubroot. It’s similar to another research method in which the clubroot pathogen is broken down into pathotypes.

This technology is somewhat different, said Yu. The team already has the clubroot-resistant line; the goal is to test how effective it is when tested against a range of clubroot races.

″Through race profiling we can predict the effectiveness of a resistant gene in a cultivar. So for example, the frequency of an avirulent gene in the clubroot pathogen is 50 per cent. That means that the corresponding resistance gene in the canola cultivar is an effective rate of 50 per cent,″ she said.  

But this is just the tip of the iceberg. The team has been working on clubroot resistance since 2011 and recently developed a new mapping-by-sequencing method and a ″pipeline″ for gene identification that accelerates the development of genetic resources.

This has set the stage for the identification of more than 20 clubroot-resistant genes and markers, including the first such gene in black mustard and the first major resistant gene in Brassica oleracea, a plant species that includes cabbage, broccoli, cauliflower, kale, Brussels sprouts and other leafy green vegetables.

They have also developed molecular markers linked to each of these genes for use in molecular breeding as well as canola and mustard germplasms for resistance to clubroot that can be used by breeders.

Molecular breeding is genetic manipulation at the DNA molecular level intended to improve characteristics of interest in a plant or animal.

Finally, researchers found that when it comes to clubroot resistance in canola, two genes are better than one. This means two genes acting in unison could manifest broad spectrum resistance to Canada’s clubroot pathogens. And it seems to work through a mathematical mystery, said Yu.

″To give a simple example, with Gene 1 the clubroot infection rate is about 50 per cent. With Gene 2, the infection rate is 40 per cent. Neither gene is resistant to clubroot at all. But if we combine Gene 1 and Gene 2 together, we got 100 per cent resistance,″ said Yu.

″So you might say in simple terms that one plus one equals more than two.″

Yu can’t overemphasize the importance of ongoing clubroot resistance in canola and other brassicas. Clubroot is one of the most serious diseases of brassicas because its spores can remain in the soil for up to 20 years.

According to the Alberta government, clubroot galls tie up soil nutrients so they can’t get to the plant. Severely infected canola also prevents transportation of water to the above-ground plant.

Clubroot rose to prominence on the Prairies about 20 years ago when canola acreage started to grow in central Alberta. Since then, it spread across the Prairies along with producers’ choice to grow canola, one of the most highly valued crops in western Canada.

Much like colds and flus in humans, clubroot spreads largely through contact. Producers’ sole initial defence included diligent crop rotations and equipment disinfection. 2009 saw the registration of the first clubroot-resistant canola cultivar in Canada.

Some of the genes identified by the Saskatoon team have been used by crop breeding companies for the second generation of clubroot resistance cultivars. Most of Yu’s recent work has focused on the third generation of clubroot resistance.

But it’s highly unlikely to end there. As with pests treated with chemical crop protection products, clubroot will continue to adapt to resistant cultivars.

″The pathogen population always evolves. There’s always something new,″ she said.

It will probably take a few years for Yu and company’s technology to be incorporated in new, ready-to-plant varieties with more diverse clubroot resistance genes, but she doesn’t think it will take too long.

″The breeding companies are very actively trying to bring new cultivars to the market in the canola industry. To my understanding, I think there are at least two sources of (clubroot) resistance on the market already with more coming, and they’re coming with diversity.″