About Blackleg of canola (BL)
BL is caused primarily by the fungus Leptosphaeria maculans. Losses of over 50% have been recorded in some fields where susceptible varieties of canola were grown. Managing BL requires an integrated management strategy using the best agronomic practices to minimize yield loss and maintain the effectiveness of genetic resistance in our varieties. There are two types of BL resistance in current varieties- major gene (race specific) and minor gene. It is major gene resistance that is at risk of being less effective in preventing yield loss. Knowing the race of BL in your fields can help you choose the canola varieties with resistance gene(s) that work against isolates present in that field.
BL Resistance Genes
Commercial canola varieties are assigned resistance ratings based on their field performance in terms of disease incidence and severity relative to check varieties in disease testing sites. The use of blackleg race or R-gene labels is voluntary. Not all varieties will have a race gene label. If you don’t see a R-gene label for the variety you are interested in using, contact the seed company or Canola Council of Canada agronomists for more information.
Identifying BL Races
BL race testing is complicated is that there is not just one BL race present in a field; testing needs to address the BL ‘population’. Correctly sampling stubble is critical to getting a valid result. Researchers have found that races interact with each other so just knowing the races isn’t enough. PSI also determines the phenotype (how the races in a field may affect the variety resistance in that field) to help guide the choice of a canola variety that offers the best resistance for that field.
Knowing the races of BL present in your field is only one of the tools you need to use to manage BL before it results in serious yield loss. Increasing the number of years between canola crops, rotating varieties, using certified seed, controlling weeds and volunteers and scouting to identify BL are all key strategies in long-term BL management.