The Lock-And-Key Approach To Managing Blackleg
Based on the 2022 Manitoba Canola Disease Survey from Manitoba Agriculture, Blackleg was found in 85% of the 115 field that were surveyed. This shows that it is very likely you have blackleg present in your fields. The fortunate news is that within the infected fields, only 13% of tested plants sampled showed infection. This means, that the current disease pressure is low but the opportunity for it to grow is high and this is our opportunity to start managing this disease. Canola acres have generally reached their maximum in the province (if we are trying to maintain good rotation practices) and as we push our rotations and continue using the same varieties, we will start to see the infection levels within fields rise.
Photos from: Canola Council of Canada, Canola Encyclopedia
The majority of canola varieties on the market do have a R (resistant) or MR (moderately-resistant) rating against blackleg disease. The current variety you are using likely has some level of protection.
Unfortunately, over the last few decades, the blackleg pathogen population has been able to overcome the resistance genes we had been relying on. Now, we are faced with several races of blackleg that have adapted to get around our resistance genes.
Recently, some companies have been doing the work of identifying what specific race of resistance genes their canola cultivars provide. This is important because of the way blackleg races interact with the 10 available race-specific resistance genes.
Think of each race of blackleg like a key that can infect any canola plant. And the resistance genes that our canola varieties carry are like a lock. When matching lock and keys connect, it locks in the resistance for the plant and prevents any further infection via that race of blackleg.
· If key A enters canola with lock A, the canola plant recognizes the key and will defend itself against the disease.
· If key A enters canola with lock B, the canola plant doesn’t recognize the key and therefore is susceptible to infection by that race of the disease.
If you have been using a canola variety that says it has an R (resistant) rating against blackleg, but you are still experiencing yield loss from blackleg on your farm, it is likely that your canola has the wrong lock mechanism for the “key” or race of blackleg that is predominant in your fields. This would indicate that you need to switch up your canola varieties to bring in the correct matching genetics.
If your farm is seeing significant increase in blackleg pressure, it will be especially important to send in stem samples for identification of what blackleg races are predominant in your fields. Then you will be able to accurately select the variety to manage the race on your farm.
If for some reason you are unable to send in samples, step 1 is to call me, Katie, or your other local agronomist to help assist with sampling in the fall. Or, be sure you are picking a canola variety that lists the stacked blackleg resistance genes to ensure protection over as much as possible.
For more information, Canola Council of Canada has a thorough video explaining blackleg resistance and management in detail on YouTube: https://www.youtube.com/watch?v=NudVxIurXSA
~Katie Meggison