Blackleg remains a significant concern for canola growers, making early assessment and informed management strategies essential. Crop scouting helps determine the level of incidence and severity, allowing growers to understand their risk heading into future seasons. As blackleg pressure evolves, improvements in resistance gene labelling and the use of stubble tests offer growers additional tools to make effective decisions.
Understanding Blackleg Risk
Crop scouting is the first step in managing blackleg (Leptosphaeria maculans). Assessing the level of incidence and severity helps growers estimate future blackleg risk. Once the disease level is understood, one of the key management strategies is crop rotation. A minimum two-year break between canola crops allows crop residue containing the blackleg pathogen to break down.
Resistance Gene Labelling in Canola Hybrids
As blackleg advances, resistance strategies continue to improve. One significant step forward has been the labelling of major blackleg resistance genes in canola hybrids, which BrettYoung has been doing for several years. This information supports growers in making more informed hybrid selections.
Canola hybrids rely on two types of resistance:
- Quantitative resistance, involving numerous genes that slow infection but are difficult to classify; and
- Qualitative (major gene) resistance, where a specific major gene stops the pathogen at the site of infection.
BrettYoung Regulatory & Agronomic Services Manager Justine Cornelsen highlighted the value of having both quantitative resistance and major gene labelling available to growers.
“With quantitative resistance, you have multiple genes working together to slow the pathogen down as it moves through the plant,” said Cornelsen. “This minimizes the overall severity of the disease but doesn’t eliminate it. Qualitative resistance is when a major resistance gene matches an avirulence gene within the blackleg population to initiate a defence response within the plant that stops the pathogen at the site of infection.”
Role of Stubble Tests
Blackleg stubble tests determine the pathogen genotype and phenotype. The phenotype provides important information about the blackleg races present in a field. An example of stubble test results includes races such as Rlm5 and Rlm6, which are not yet found in Canadian germplasm.
Avirulence Gene Presence in Western Canada
AvrLm7 is one of the most predominant blackleg avirulence genes in Western Canada. With the addition of the Rlm7 resistance gene in canola hybrids, many growers experiencing blackleg issues may see improved success in reducing disease pressure, as Rlm7 matches 90% of L. maculans races detected in the region. Higher frequencies of avirulence genes increase the likelihood that corresponding R genes will be effective.
FAQ
What is the first step in managing blackleg in canola crops?
Crop scouting to assess the incidence and severity of blackleg.
How does crop rotation help manage blackleg?
A two-year break between canola crops allows infected residue to break down, lowering disease risk.
What is the difference between quantitative and qualitative resistance?
Quantitative resistance uses multiple genes to slow infection, while qualitative resistance uses a major gene that stops the pathogen at the site of infection.
Why are blackleg stubble tests important?
They identify the blackleg races present in a field, helping growers choose effective resistance genes.
Which avirulence gene is most common in Western Canada?
AvrLm7, which is significant because Rlm7 matches 90% of regional L. maculans races.
