Crop scouting is always the first step when managing blackleg (Leptosphaeria maculans). Assessing the level of incidence and severity of blackleg in the field will help growers to develop an estimate of blackleg risk for the future.
There are two main management strategies once growers know what they’re dealing with, one being crop rotation. A minimum two-year break between canola crops allows for crop residue housing the blackleg-causing pathogen to break down.
Fortunately, as blackleg advances, so do we. One of the biggest steps some of the industry has taken recently is labelling the major blackleg resistance genes found in canola hybrids, something BrettYoung has been doing for several years. This is important information as it can be used to rethink the approach towards effective blackleg management. Canola hybrids use two sources of resistance — quantitative and qualitative (major gene).
Quantitative resistance is a sort of “catch-all”, meaning it has numerous genes working together to slow the infection of blackleg in your canola plants. Because quantitative resistance has so many genes working within it, it’s more difficult to classify and harder to screen for. Qualitative resistance, on the other hand, are major genes that stop the pathogen at the site of infection. BrettYoung Regulatory & Agronomic Services Manager Justine Cornelsen said the industry’s shift to labelling major genes, paired with quantitative resistance, is really helpful as it provides more information to growers to assist in hybrid selections.
“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 defense response within the plant that stops the pathogen at the site of infection.”
Blackleg stubble tests determine the pathogen genotype and phenotype, the phenotype being the important information for growers with blackleg concerns as it shows growers the blackleg races present in their field.
One of the most predominant blackleg avirulence genes in Western Canada is AvrLm7. With the addition of the Rlm7 resistance gene to canola hybrids, Cornelsen said there’s a good chance most growers with blackleg issues will have much stronger success in minimizing disease pressure if they’re growing a hybrid with that major gene as it matches 90% of L. maculans races detected in the region.
