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Decreased Sensitivity of Leptosphaeria maculans to Pyraclostrobin in Alberta, Canada
Yixiao Wang1, Alireza Akhavan1, Sheau-Fang Hwang1
1Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB T6G 2P5, Canada.
Abstract:
Leptosphaeria maculans, the causal agent of blackleg of canola (Brassica napus), can be managed with pyraclostrobin and other strobilurin fungicides. Their frequent application, however, poses a risk for the development of insensitivity in fungal populations. A collection of L. maculans single-spore isolates recovered from infected canola stubble in Alberta, Canada, in 2016 was evaluated for its pyraclostrobin sensitivity. In conventional growth plate assays, the concentration of pyraclostrobin required to inhibit fungal growth by 50% (EC50) was determined to be 0.28 mg/liter in a subset of 38 isolates. This EC50 was four times greater than the mean EC50 (0.07 mg/liter) of baseline isolates collected in 2011. Two hundred sixty-three isolates were screened further with two discriminatory doses of 0.28 and 3.5 mg/liter of pyraclostrobin, resulting in growth inhibition values ranging from 16 to 82% and 41 to 100%, respectively. In microtiter plate assays with the same isolates, the mean EC50 was determined to be 0.0049 mg/liter, almost 3.3 times greater than the mean EC50 (0.0015 mg/liter) of the baseline isolates. The sensitivity of the isolates was also evaluated in microtiter plate assays with discriminatory doses of 0.006 and 0.075 mg/liter of pyraclostrobin, resulting in inhibition values ranging from 20 to 88% and 49 to 100%, respectively. This is the first report of isolates of L. maculans with increased insensitivity to pyraclostrobin in Canada, suggesting the need for improved fungicide stewardship.
Insights
Fungicide resistance is emerging in Leptosphaeria maculans, the pathogen causing blackleg in canola crops. This study found increased pyraclostrobin insensitivity in Canadian fungal populations, highlighting the need for better fungicide management.
Area of Science:
- Agricultural Science
- Plant Pathology
- Fungal Genetics
Background:
- Blackleg, caused by Leptosphaeria maculans, is a significant disease affecting canola (Brassica napus).
- Strobilurin fungicides, including pyraclostrobin, are commonly used for blackleg management.
- Frequent fungicide application can lead to the development of insensitivity in fungal populations, posing a threat to disease control.
Purpose of the Study:
- To evaluate the sensitivity of Leptosphaeria maculans isolates from Alberta, Canada, to the fungicide pyraclostrobin.
- To determine if pyraclostrobin insensitivity has emerged in Canadian L. maculans populations.
- To provide data supporting improved fungicide stewardship strategies.
Main Methods:
- Collection of L. maculans single-spore isolates from infected canola stubble in Alberta, Canada (2016).
- Determination of pyraclostrobin EC50 (effective concentration inhibiting 50% of fungal growth) using conventional growth plate and microtiter plate assays.
- Screening of isolates using discriminatory doses of pyraclostrobin.
Main Results:
- A subset of isolates showed a mean EC50 four times greater than baseline isolates from 2011 in growth plate assays.
- Microtiter plate assays revealed mean EC50 values approximately 3.3 times higher than baseline isolates.
- Screening with discriminatory doses indicated a range of growth inhibition, with some isolates showing reduced sensitivity.
Conclusions:
- This study reports the first evidence of L. maculans isolates with increased insensitivity to pyraclostrobin in Canada.
- The findings suggest a potential risk of reduced efficacy of pyraclostrobin for blackleg control.
- There is an urgent need for enhanced fungicide stewardship practices to preserve the effectiveness of pyraclostrobin.
