The Challenge

All commercially available cultivars rate as R or MR for blackleg, but severe blackleg infection (up to 100% disease incidence) has been found in fields across the prairies in 2012.

The Project

Identify new virulent races of L. maculans that are at high risk for overcoming specific R genes by monitoring pathogen race dynamics through yearly analysis of Avr gene prevalence.

The Results

AvrLm2, AvrLm4, AvrLm6 and AvrLm7 were found at high frequencies, while AvrLm1 and AvrLm3 were generally low. Rlm3 and Rlm1 are the more commonly R-genes found in Canadian cultivars, therefore other mechanisms may be influencing resistance such as quantitative and/or nonspecific race resistance.

Grower Benefits

By mapping the distribution of various blackleg races, better management strategies can be developed based on rotating resistant varieties carrying specific resistant genes. Caution should be used when recommending canola cultivar rotation based on specific R-genes as the pathogen can change substantially from one field to another. Where blackleg severity is high, longer crop rotation should be the first line of defence.

Keywords: Blackleg, Quantitative resistance, R genes, Resistance breakdown, Leptosphaeria maculans, L. maculans, Major gene resistance, Rlm3, Rlm1