Yield losses in blackleg of canola and pyraclostrobin sensitivity in populations of Leptosphaeria maculans
Peer Reviewed StatusNon-Peer Reviewed
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Blackleg of canola (Brassica napus L.), caused by Leptosphaeria maculans (Desm.) Ces.& de Not., is an important disease worldwide. In Canada, blackleg is managed mainly by the cultivation of resistant or moderately resistant canola hybrids and fungicide application. A field experiment was conducted in central Alberta to determine the relationship between blackleg severity and yield in two moderately resistant hybrids 73-15RR and 1950RR. Seed yield per plant was found to decrease as a consequence of L. maculans infection, with regression analysis showing that the relationship between yield and disease severity was best explained by second degree quadratic equations. Sensitivity to the fungicide pyraclostrobin, a strobilurin that is commonly applied as a foliar and seed treatment for blackleg and other diseases, was evaluated in 12 and 250 isolates of L. maculans collected in Alberta in 2011 and 2016. The half-maximal effective concentration (EC50) of pyraclostrobin was determined, and two discriminatory doses of the fungicide were used to identify highly insensitive isolates in the collection. The mean EC50 value was significantly higher for the isolates collected in 2016 (0.28 mg L-1) versus those collected in 2011 (0.07 mg L-1). Nonetheless, while all isolates were still sensitive to pyraclostrobin, the increase in mean EC50 observed in the more recent L. maculans collections suggests that proper fungicide stewardship is warranted.
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