Clubroot is breaking down canola variety resistance and proving to be a worthy adversary in Alberta.
Spores from the clubroot type identified last year as 5X have now been found in 16 fields, some of them hundreds of kilometres apart.
“I think geographically it’s surprisingly distributed over a larger region than maybe anticipated,” said Canola Council of Canada agronomy specialist Dan Orchard.
The soil-borne disease has been gradually spreading on the Prairies, where it has potential to drastically reduce canola yields.
Researchers speculate that the apparent spread of the 5X strain is a matter of percentage. A certain number of spores of various clubroot types are in the soil. Resistant canola varieties withstand some types but not others, creating selection pressure.
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The Alberta Canola Producers Commission issued a news release about resistance breakdown last week, raising alarms about suspicions of multiple virulent types of clubroot.
“The news release came out a little bit on the scary side,” said Orchard.
“In a way, it’s kind of a good news story to learn that our industry can react so quickly to something. Kind of a good and bad story combined.”
Clubroot’s ability to surmount resistance in canola is not a surprise, nor does it indicate that “the end is near,” said Bruce Harrison, director of research and development with Crop Production Services Canada.
Last week, his company announced promising new varieties showing resistance to clubroot pathotype 5X, as well as pathotypes 2, 3, 5, 6 and 8.
“We’ve been working on it for awhile, probably as long as anyone else, but we’ve taken a bit of a different approach,” said Harrison.
“We looked at it as, first of all that there were very few known disease resistant sources for clubroot, so rather than rushing out and moving ahead with just a single dominant gene, we decided that we’d take the strategy to start stacking genes as soon as we had those sources available and that we would hopefully create a more durable disease resistant hybrid as a result of that.”
Canola varieties resistant to clubroot have relied on one dominant gene. That is assumed to have contributed to the disease’s relatively swift ability to overcome resistance.
Harrison said the new canola varieties have yet to be field tested, and in fact will be tested against 5X in pots rather than fields at this stage.
Crop Production Services is partnering with University of Alberta and Agriculture Canada researchers on variety development and testing.
“As we get further down the path here with germplasm development and as we understand more about the genetics that we’ve got … I think it allows us to … ensure we are bringing along the right genes, whether that be a collection of blackleg resistance genes in combination with clubroot, or whatever,” he said.
“We will achieve more durable and more robust clubroot resistance by stacking genes, but second of all, we would also say that it doesn’t matter if you’ve got the best clubroot (resistance) in the world if you don’t have really solid blackleg resistance. It’s really part of a platform that we’re developing.”
Orchard said Crop Production Services’ news about potential new genetics was welcome.
“It is encouraging because obviously we know now that there’s companies behind the scenes very aggressively working at this,” he said.
Harrison was also measured in his response.
“We don’t feel as though we’ve arrived,” he said.
“Its more that we’re viewing clubroot like blackleg, where pathotypes will change, and we’ll need to incorporate new genes in the future to ensure that we have this ongoing protection.… We’ve at least found some sources in combination that are proving to be really quite effective.”
Until those new varieties become available, Orchard is worried about the gradual spread of clubroot, which is at least partly because farmers aren’t using resistant varieties.
“There are still some pockets kind of on the fringe of where clubroot is starting to get established that are a little bit behind in adopting the use of clubroot resistant varieties, so that’s a little bit of a concern,” said Orchard.
“We strongly advise using the resistants before the disease shows up, and that doesn’t seem to be the case along the leading edge of clubroot. It seems like we’re still chasing it a little bit.”
Orchard said he doesn’t know why some farmers aren’t adopting resistant varieties. Seed cost and yield potential are similar between resistant and non-resistant varieties, so those aren’t issues, but supply or simple delivery logistics might be factors.
“It could just be the simple fact that growers find a variety they like and they stick with that variety. That’s understandable.”
barb.glen@producer.com
