Agronomists agree the best way to control blackleg in canola is rotation — only growing canola once every three years, at most. Besides rotations, scouting and fungicide can help in the fight against blackleg. And, last spring a new item was added to the list of blackleg-fighting tools: a new labelling system.
This season, you’ll see some new letters on some of your seed bags: A, B, C, D, E1, E2, F, G, H and X. First, what does this mean for you? Then, why aren’t those labels on all the bags?
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There are two ways to breed defence against blackleg into canola.
1. Major genes: Major gene resistance is strong and specific, stopping pathogens at the site of the initial infection. A defense response from the plant is initiated when avirulent proteins in the blackleg pathogen match the major resistance gene in the plant. Researchers have documented 12 main avirulence genes in Canadian blackleg. Breeders have incorporated major genes into new varieties to provide targeted defence.
Unfortunately, the major gene in your seed will not always be a “match” for the specific blackleg races in your field. And, the blackleg races in your field will evolve over time.
2. Minor genes: Minor gene resistance is weaker, and non-specific, involving several genes working together to reduce infection in adult plants. Because it is harder for blackleg races to overcome, minor gene resistance is likely to be effective for a longer period of time.
“The ideal canola variety would have both major gene resistance and quantitative [minor gene] resistance, giving the plant two main ways to manage the disease pressure,” Justine Cornelsen, Canola Council of Canada agronomy specialist wrote in an email.
The new seed labeling system is based on major gene resistance.
If you’ve had a blackleg problem, the Canola Council says: “Rotating varieties creates the opportunity to bring a mix of resistance genes to the field over time, which can reduce selection pressure and improve durability.”
Or, to be certain of matching the race in your field with your variety, you can have your canola stubble tested by Discovery Seed Labs. These tests cost $190 per sample (though costs may go down as more labs start to offer testing.)
Some labels in place
If you’ve purchased seed from DEKALB, CANTERRA SEEDS or Brett Young, you can check the label to see which blackleg resistance gene is in your seed. However, not all seed companies are adding these labels.
Bayer is not planning to label its Invigor canola seed with the new system. Jared Veness, field marketing manager with Bayer CropScience Inc., listed two issues that keep Bayer from labeling at this time: sampling issues and minor gene contributions.
Veness says growers’ sampling accuracy in a large field is unlikely to be 100 per cent, which would mean growers could potentially choose a variety that would not be resistant to the blackleg race(s) in their field.
Veness is also concerned about the fact that minor gene resistance is not included in the labeling system. While researchers agree that minor genes contribute to blackleg resistance, there is no consensus about how to measure and label that resistance. With no information about minor genes included in the labeling system, breeders may place a lower priority on minor genes.
Veness believes Bayer’s Invigor canola has strong minor gene resistance to blackleg. With over 50M acres of Invigor canola in the ground in past years, Veness says, there have been “less than a handful of blackleg complaints.”
Crop Protection Services will also not be adding these new labels to its Proven Seed varieties.
Bruce Harrison, CPS’s senior director of breeding and innovation, is also concerned about the inability to measure and quantify the impacts of minor resistance genes.
We’re learning more about how these genes function all the time, Harrison says. “We need to make sure that we’re developing a durable strategy for the long-term health of the industry.”
“Blackleg management needs to be an integrated pest management approach,” wrote Justine Cornelsen, “with the focus relying heaving on extending crop rotation, proper scouting/identification of the disease and use of resistant canola varieties.”
Visit the Canola Council of Canada website for more information about blackleg.