Canadian canola growers have been able to keep blackleg at bay for the past 15 years by following strict rotations and growing resistant varieties.
Recent research shows the importance of adhering to that practice.
Randy Kutcher, a research scientist at Agriculture Canada’s research centre in Melfort, Sask., said the blackleg pathogen is evolving so that it is able to overcome resistance.
Growers who push their rotations are taking a risk that the pathogen will mutate and affect a subsequent crop.
Read Also
Man charged after assault at grain elevator
RCMP have charged a 51-year-old Weyburn man after an altercation at the Pioneer elevator at Corinne, Sask. July 22.
Increased disease severity has been reported in some areas, particularly in southern Manitoba. Southeastern Saskatchewan has also seen a resurgence of the disease.
Kutcher and other researchers have been examining the new pathogens in an effort to help breeders develop new varieties. Results of their most recent studies were recently published in the Canadian Journal of Plant Pathology.
Key among those results is the identification of at least 14 races of the pathogen and possibly 16.
Kutcher said the culprit was the introduction of specific resistance genes in canola varieties.
“When you introduce resistance genes, the pathogen’s goal is to try and survive,” he said. “It’s responding to those genes for resistance that are in those cultivars and so that’s why you get variability.”
He said the combination of possibilities leads to the races.
“We have outgrown the old system of resistant or susceptible,” Kutcher said.
The pathogenecity (PG) classification system isn’t as useful as it once was because it is based on only three or four resistance genes, he added.
Kutcher’s research examined a random sample of 96 isolates from across the Prairies. He said researchers don’t yet know if the 14 confirmed genes are all different. Some of them are worthless.
“In Europe, (genes numbered) one, two, three, four and nine, that’s five genes that are pretty much totally useless,” he said.
“The pathogen population has overcome all of those genes and so now they’re depending on number seven.”
The number of genes is not endless, Kutcher added, which means the resistant ones must go into varieties as soon as possible and last as long as possible. Gene number six looks like a good bet for Canada because the 96 isolates all showed resistance.
He said Canadian farmers shouldn’t be too worried about the increasing pathogens.
“We have very good resistance and I guess what growers should know is that rotation really does have an effect to keep those infected stem pieces disintegrating before they plant their next crop.”
Darwin Hammond, senior agronomist with the Canola Council of Canada in Manitoba, said three-quarters of 49 fields surveyed in south-central Manitoba had blackleg. Eight percent contained the basal stem cankers that most affect yield.
“It’s probably not highly significant yet.”
However, Hammond said growers should take note when infection nears 10 percent in resistant varieties.
“There are growers that have been in fairly tight rotations,” he said.
He advised canola growers to scout fields in the fall to check for disease and make a strong effort to positively identify the disease rather than just assume they know what it is.
Higher levels of blackleg were found in a field where the farmer had seeded winter wheat into canola stubble.
The winter wheat didn’t survive, so the farmer grew canola again. That rotation is too close for comfort, he said.
Growers should also remember that even resistant varieties may contain up to 30 percent disease. Resistance does not mean immunity.
Kutcher said breeders will be able to use his research to select genes for their programs and develop new resistant varieties.
“The chances of us eliminating it would be rather slim.”
He also said a variety’s resistance can be overcome quickly.
“What has happened in Europe and Australia is that it’s quite sudden. A variety that worked well for 10 years, all of a sudden, oh, there’s a lot of blackleg there this year.”
