Blackleg pathogens studied to rate canola resistant cultivars

EDMONTON — Farmers can no longer rely just on cultivar resistance to combat blackleg, says Ralph Lange of Alberta Innovates Technology Futures.

Incidence of blackleg started to increase rapidly in Alberta in 2011 when 80 to 90 percent of the canola in a field near Irma showed symptoms of the disease.

“We don’t see hundreds of fields like this, but every year, I’d say there’s dozens, so blackleg is coming back,” Lange said during his April 6 presentation at Murray Hartman’s Science O-Rama in Edmonton.

Lange is working to develop resistant groups of canola cultivars to help producers better manage the blackleg resistant genes that are currently available.

Canola varieties are already assigned resistance ratings for blackleg in Canada, but Lange would like to implement a system similar to what is in Australia.

That country places blackleg resistant cultivars into groups with similar genetic resistance to the disease so that producers can rotate different kinds of blackleg resistance in their fields.

“Those resistance groups ultimately are based on the resistance genes of the canola variety,” he said.

“You’re throwing different genes at the pathogen population that doesn’t know about the mode of attack, and you’re preventing the resistance to genes.”

Lange is attempting to determine if a similar system would work in Canada by growing multiple canola varieties in a lab and exposing them to blackleg pathogens in canola straw he collected from multiple locations.

“That way, we could expose a bunch of varieties to a bunch of crop residues, and based on this information, see if we could make resistance groups,” he said.

“So it’s a feasibility study to see if we could group Canadian cultivars.”

Lange said his work has shown that the concept has potential in Canada, but the pattern of the blackleg pathogen is different in Australia then in Canada.

Blackleg in the sexual stage makes pseudothecia, which is visible on stubble in Canada but not as common in other parts of the world, including Australia.

“The infections we were getting were maybe five to 10 percent of the plants. When we look at the stubble, we do see some ascospores in there. I think it’s realistic about what happens in Canadian fields, but it’s unlike the Australian system,” he said.

“I think we are getting a lot lower inoculant pressure.”

Lange is concerned that the level of blackleg inoculant may not have been uniform in his study because it collected crop residues from the field.

“So how do we tell that the results we are seeing are due to pathogen change or due to the genetics on either side or simply due to simply disease pressure?” he said.

Lange is planning a second study with procedures that ensure uniform disease pressure to validate the results of the first study.

Researchers must first understand the variability in the blackleg pathogen types found on the Prairies before they can effectively group canola cultivars.

Lange said researchers already know quite a bit about blackleg pathogen genotypes in Canada.

To learn more, Lange and his research group sent blackleg samples to Agriculture Canada’s lab in Saskatoon, which genotyped the isolates into nine virulence genes and then developed a system that placed pathotypes into groups.

The study did find variability in the pathogen types across the Prairies.

“The Alberta isolates, for the most part, fall into the B group, but some in group C also, which is a little bit different than results that are coming out of different parts of the country,” Lange said.

“When we look at individual fields, they tend to have a maximum of two different pathotypes. In other words, there is not a whole lot of pathogenic variability within the province, less than we might have thought.”

He said relatively low pathogenic variability in prairie blackleg is good news, but it will make it harder to create a resistance group scheme.

Lange also hopes to include adult stage resistances to group canola cultivars.

He is currently testing adult stage canola cultivar resistances by poking leaves to simulate wind-created wounds, spraying a spore mixture on the plants and then growing the canola plants in greenhouses under heavy disease pressure.

He said he would have more results within a couple months.

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