Fungicide sensitivity and resistance in the blackleg fungus, Leptosphaeria maculans, across canola growing regions in Australia.

Dr Angela Van De Wouw1, Dr Jack Scanlan1, Dr Steve Marcroft2, Dr Leanne Forsyth3, Dr Alexander Idnurm1

1University Of Melbourne, Parkville, Australia,
2Marcroft Grains Pathology, Horsham, Australia,
3Syngenta Crop Protection, Macquarie Park, Australia

Fungicide use has become a fundamental part of many crop protection systems around the world, including to control blackleg disease on canola. In Australia, most growers routinely apply at least one, and potentially multiple, fungicides with different modes of action in a single growing season. There is evidence for the emergence of resistance to the demethylation inhibitor (DMI) class of fungicides in Australia, however it is unknown whether resistance exists towards other chemical classes, such as the succinate dehydrogenase inhibitors (SDHI). In this work, we screened the levels of resistance towards seven fungicide treatments in stubble-borne L. maculans populations across eight canola-growing regions of Australia from 2018 to 2020, a time frame that bridges the introduction of new chemicals for blackleg control. We confirmed that DMI resistance in L. maculans is pervasive across all canola-growing regions, with approximately 15% of fungal populations displaying high levels of resistance towards the DMI fungicides. Whilst resistance to newly introduced SDHI fungicides is low, we found evidence of positive cross-resistance between established DMI-only fungicides and a newly introduced combined DMI and quinone outside inhibitor (QOI) fungicide treatment, suggesting the efficacy of the latter may be limited by widespread DMI resistance. Proactive surveillance, such as that performed here, may provide a means to avoid the rapid loss of fungicide efficacy in the field.


Angela’s research combines molecular and applied approaches for managing blackleg disease.



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