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5 July 2016 Sensitivity of Leptosphaeria maculans to pyraclostrobin in Alberta, Canada
Michelle Fraser, Sheau-Fang Hwang, Hafiz U. Ahmed, Alireza Akhavan, Gerd Stammler, Wayne Barton, Stephen E. Strelkov
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Strobilurin fungicides can be used to manage blackleg (Leptosphaeria maculans) of canola (Brassica napus); however, they have a high risk of selecting for resistance in fungal populations. In 2011, single-spore isolates of L. maculans were obtained from infected canola stubble representing six fields in Alberta, Canada. The isolates were grown on fungicide-amended agar plates and percent growth inhibition was calculated based on colony diameter relative to non-amended controls. Using probit regression analysis, the effective concentration of pyraclostrobin needed to inhibit mycelial growth by 50% (EC50) was determined to be 0.09 mg L-1 based on 13 isolates. To identify highly insensitive isolates, 117 isolates were grown on agar plates amended with a discriminatory dose of 6.25 mg L-1. Isolates in which growth was inhibited <50% were considered insensitive. Growth inhibition values ranged from 66.6% to 100.0% with a mean of 84.3%, indicating that all of the isolates were sensitive to pyraclostrobin. Forty-one of the 117 isolates were also tested via a microtiter plate assay. Based on conidial germination and subsequent growth, the EC50 values obtained for each isolate ranged from 1.0 × 10-4 to 7.4 × 10-3 mg L-1, which were not significantly different from those of the sensitive controls (4.1 × 10-3 and 5.7 × 10-3 mg L-1). While pyraclostrobin insensitivity was not detected in L. maculans populations from Alberta, continued monitoring will be necessary to track future changes.

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Michelle Fraser, Sheau-Fang Hwang, Hafiz U. Ahmed, Alireza Akhavan, Gerd Stammler, Wayne Barton, and Stephen E. Strelkov "Sensitivity of Leptosphaeria maculans to pyraclostrobin in Alberta, Canada," Canadian Journal of Plant Science 97(1), 83-91, (5 July 2016).
Received: 22 December 2015; Accepted: 1 May 2016; Published: 5 July 2016

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aux fongicides
Brassica napus
Brassica napus
fungicide sensitivity
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