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Survey of resistance to fungicides in cucumber downy mildew

Project Code: PRR17-030

Project Lead

Geneviève Marchand - Agriculture and Agri-Food Canada


Assessment of resistance to single-site fungicides in populations of cucumber downy isolates from field and greenhouse production sites in Ontario and Quebec

Cucurbit downy mildew is an important disease of cultivated cucumbers in the field and in the greenhouse. It is caused by the oomycete pathogen Pseudoperonospera cubensis and is spread primarily by airborne spores. Severe infections can result in rapid crop failure, with foliage completely blighted within 10 days from first symptoms. It was identified as a priority pest issue by Pesticide Risk Reduction. Conventional fungicides are commonly used to control the disease. Single-site, systemic fungicides are more effective than multi-site; however, the pathogen is known for its ability to rapidly develop resistance to single-site fungicides. By sampling in commercial cucumber production sites in Ontario and Quebec, the project will document the extent of resistance to the commonly-used single-site fungicides in pathogen populations. In vitro and in vivo assays will be used to evaluate the resistance profile of Pseudoperonospera cubensis isolates.

A molecular Polymerase chain reaction (PCR)-based tool may also be developed to validate existing protocols and to test for resistance to specific single-site fungicides. Bypassing the need to handle pesticides, which is required in traditional screening methods, will allow for a quicker and easier way of conducting screening and determining the resistance profiles of the pathogen. Once developed, the simplified process may be used for testing of pathogen resistance to fungicides by commercial diagnostic labs.

Knowledge generated through this study could help growers make informed disease management decisions while taking into account the efficacy of registered fungicides in specific areas in the major growing regions of cucumber in Canada.

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