Researchers say better gene classification will help match blackleg-resistant canola varieties to races of the fungus found in the field.
AAFC Saskatoon has unveiled tools to quickly identify avirulence proteins (which facilitate plant infection) in submitted samples, attendees of Canolapalooza heard June 21 in Portage la Prairie.
Harunur Rashid, graduate student with the University of Manitoba plant science department and one of the instructors June 21, said the new resistance gene (R gene) labelling tools are a step forward, given how quickly the pathogen mutates and the narrow window of major gene resistance.
“If we want to get black and white resistance, 100 per cent resistance, we need to match up the resistance genes with the corresponding avirulence genes from the pathogen side,” Rashid said.
While blackleg-resistant varieties have worked to control the disease since the early ’90s, researchers have noted an increase in resistance breakdown. Virulence changes were already being noted by the late ’90s, according to Canola Council of Canada, and recent years have seen increasing instances in varieties once thought safely resistant.
Last year, blackleg was the second most prevalent canola disease in the province, according to Manitoba’s annual canola disease survey. A total of 82 per cent of surveyed fields reported the disease, although instance rates remained low, hovering around 12 per cent. The numbers were a slight increase over 2015, but below the 2014 peak, which saw well over 90 per cent of fields test positive.
Major gene resistance is qualitative, takes effect at the seedling level, and may be more effective against the fungus, but is also highly specific to race. If resistance genes match, the plant will kill cells around an infection point, creating a series of dark rings on the cotyledon, but isolating chance of further harm, Canolapalooza instructor Sakaria Liban of DL Seeds said.
“The pathogen has nowhere to grow, so it can’t spread and, at the end of the season, you’ll see clean stems if you have this kind of reaction throughout your field,” he said.
Alternately, he added, a variety may tap into minor gene, or quantitative resistance, which has a broader genetic scope, but affects the fungus in adult plants and reduces, but does not eliminate, damage from the disease.
“You’ll still get a little bit of an infection but it’ll still have this little bit of a dark ring around it and it’ll try to reduce and stop the infection,” Liban said.
“For some fields, you’ll see like 100 per cent — one gene will give you 100 per cent protection to all the samples in there, that’s great,” he said. “In some fields, you’re going to need a combination or it’s only going to give you maybe 20-30 per cent protection, so there’s variation. On average we’ve seen that some genes are stronger than others.”
Several labs will be set up for blackleg race testing by the end of 2017, Canolapalooza attendees were told.
Rashid said the tools will be particularly helpful to producers who continue to see blackleg, despite buying resistant varieties.
The University of Manitoba researcher estimates that thousands of tests will be performed this year to isolate blackleg race.
Experts have often pointed to longer crop rotations to manage disease, including blackleg, but researchers now suggest that should be taken a step further.
“We are suggesting to people, use the different groups of resistance genes in a rotation in the different years,” Rashid said. “For example, this year, if you use the Group A resistance genes and you see there are susceptible (crops) — there is the disease in the field — we will suggest to you, please, next year, please use another group of genes.”
That call has been echoed by both the Canola Council of Canada and Manitoba Agriculture.
“Utilizing the same resistance genes repeatedly in the field over time can select for races of the fungus that are virulent against that resistance,” the council advises. “The higher the frequency of growing the same variety, the greater the risk.”
Ideally, that rotation should take place within a longer crop cycle. At least two or three years should pass between canola crops on a field, the council has said, a deviation from the popular canola-wheat-canola rotation.