As blackleg resurges in Western Canada, canola growers and agronomists have been calling for seed companies to label the blackleg resistance genes on their varieties. Those labels would allow farmers to rotate resistance genes when one resistant variety breaks, the thinking goes.
“We’ve been engaged with the industry over the last few years to see if there is a new type of labelling system that we can come up with,” says Clint Jurke, agronomy director for the Canola Council of Canada.
Jurke adds it seems like most of the industry is ready to adopt new labels. “It’s just a matter of working out the details of what this new classification system looks like.”
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But some in the industry have reservations about labelling resistance genes. While it might seem simple to rotate the resistance genes, that might not best serve the industry, says Stewart Brandt, breeding operations manager at Bayer CropScience.
Australia has been labelling blackleg-resistance genes, so why not Canada? Brandt points out growing conditions are different between the two countries. “We have a much different growing season. It’s much shorter. We have a very harsh winter. They don’t.”
But a lot of it comes down to major and minor gene resistance.
Major gene, or qualitative resistance comes from a single gene, Godfrey Chongo, plant pathologist for Bayer, explains. Major gene resistance only affects specific strains of the disease.
“But it’s also very effective from the seedling stage onwards,” says Chongo. That effectiveness is also an Achilles’ heel, as it puts a lot of selection pressure on the pathogen.
Minor gene, or quantitative, resistance comes from many genes. Each gene only contributes a little to the overall resistance. It’s effective against a broad spectrum of strains of the disease. Minor gene resistance doesn’t protect seedlings, but does protect adult plants.
Because minor gene resistance comes from so many genes, it’s difficult for plant breeders to work with. But it doesn’t put much selection pressure on the pathogen, says Chongo. “And for that reason it tends to be more durable.”
Jurke says about half the canola varieties on the market are believed to have good minor gene resistance, as well as major gene. Australia, on the other hand, has focused on major genes in its blackleg-resistant canola varieties, Brandt says.
Brandt worries that labelling major genes will remove the incentive for plant breeders to incorporate minor genes in blackleg-resistant varieties. Because minor genes are more difficult to work with, Brandt says, “it starts to become a question of how much do we resource something that we don’t put on the bag?”
Jurke acknowledges the new labelling system is “likely not going to be perfect.” But it will evolve and improve over time, he says. Right now, it’s a “crap shoot” whether or not farmers are incorporating a new type of blackleg resistance when they rotate varieties. “It’s not even an educated guess.”
Choosing a variety with different resistance genes will be a “much better choice than just picking another variety and hoping that you’ve got a different type of resistance,” says Jurke.
The current proposal, Jurke says, is to identify the major resistance genes while retaining the old labelling system. The old labelling system, which comprises ratings such as Resistant and Moderately Resistant, would encompass minor genes, he explains.
The long-term plan is to label minor gene resistance as well, Jurke says, but assessing minor gene resistance is complex. “You need to have a screening program that will remove the effect of the major resistance genes, so you’re just left with the quantitative.”
Jurke says they’re working with researchers to come up with a quicker process to assess minor gene resistance, which they’ll make available to all the life science companies. While that process needs improvement “the technology is certainly there to identify the major resistance genes quite easily now.”
As for Brandt, he thinks we need to better understand how blackleg overwinters, and why Canada’s infestations haven’t been as severe as in Australia. He points out we don’t know how many different blackleg strains exist in any given field, or how many genes are involved in resistance.
But he sees an opportunity in the industry to focus on both major and minor gene resistance.
“And I think most breeders try to do this,” says Brandt. “They see that it has definite benefits for performance consistency for their growers and for growers in Western Canada.”
As for Jurke, he sees labelling resistance genes as one more tool to manage blackleg. Over the last five years, the disease “has been creeping up,” says Jurke. “And it’d sure be nice if we could knock that back down.”