Blackleg in Canola

What is blackleg?

Blackleg disease of canola is caused by fungal pathogens of the genus Leptosphaeria, with the species L. maculans being regarded as the most dangerous. Infections occur after spores from previous years’ stubble are released, with spores being carried by wind or rain splash to the host plant. After the spores germinate on the leaves of a host canola plant infection continues down to the base of the stem where severe infections cause ‘stem canker’; pinching of the stem which restricts the flow of water and nutrients to the rest of the plant, resulting in yield loss. The Canola Council of Canada warns that even moderate infection can result in a significant drop in yield – https://www.canolawatch.org/2017/09/13/seed-how-much-blackleg-before-i-need-to-think-about-rotating-resistance/

 

My variety has an R rating for blackleg, so why do I see infections?

Current blackleg ratings are determined after co-operative field trials conducted by WCC/RCC across western Canada. An ‘R’ rating means a variety had an average infection severity across multiple trials that was less than 30% of the susceptible check (Westar) overall. It does not mean that the variety is resistant to all races of L. maculans or to the races found on your farm specifically. Many canola varieties carry specific resistance genes, which only defend against races of L. maculans which have the corresponding avirulence phenotype. L. maculans populations vary across western Canada, so a given resistance gene may not be effective in your area. Several other pathogens, including root rot-causing fungi such as Fusarium, can also produce discolouration within the stem which is easily confused for blackleg.

 

Why test?

Sending suspected blackleg infected stubble in for testing will firstly determine if what you’re seeing is actually blackleg. If L. maculans is found in your sample the blackleg race testing protocol will be able to determine which avirulence genes the isolates carry. This information can then be taken to your seed supplier or agronomist and used to help select a canola variety carrying suitable resistance genes to defend against the L. maculans found in your field.

 

Cost of testing

Presence/Absence of blackleg (L. maculans) – $95.00 per sample.

Identification of specific blackleg race – $95.00 per sample.

 

Blackleg Sampling Fact Sheet