Assessing Fungicide Sensitivity in Sclerotinia sclerotiorum
Term: 3 years
Status: Ongoing
Researcher(s): Dwayne Hegedus, Lone Buchwaldt, Edis Dzananovic, AAFC
SaskOilseeds Investment: $28,875
Total Project Cost: $793,200
Funding Partners: RDAR, ACPC, MCGA
Objective
Testing for fungicide sensitivity in Sclerotinia sclerotiorum. Four hundred S. sclerotiorum isolates will be screened for resistance to three fungicides: pydiflumetofen, fluopyram and fludioxonil.
Identify the molecular basis of fungicide insensitivity. Genes encoding fungicide targets will be sequenced from resistant and susceptible isolates and examined for genomic mutations that contribute to resistance.
Development of diagnostic assays and tools. Where possible, molecular markers tightly linked to mutated genes will be developed that will detect fungicide insensitive isolates more rapidly than the current mycelium growth-rate assay.
Project Description
Sclerotinia sclerotiorum is a fungal pathogen of canola and many other crops including bean, soybean, sunflower, potato and lentil. Brassica napus germplasm with high levels of quantitative resistance have been identified and are being crossed into breeding lines with good yield, early maturity and canola-quality seed contents.
Furthermore, Corteva Agriscience is marketing canola varieties with some level of sclerotinia resistance that may need fungicide application when the disease risk is high. Taken together, fungicide application will remain a valuable tool for canola growers in the foreseeable future.
It is important for all stakeholders in the canola industry to know whether resistance to certain fungicides occurs in Canada. The global Fungicide Resistance Action Committee (FRAC) has grouped each fungicide active ingredient according to the metabolic pathway that is targeted in fungal plant pathogens. In China, where sclerotinia is endemic and fungicides are sprayed routinely, resistance in S. sclerotiorum has developed to Group 1 (benzimidazoles: e.g. carbendazim), Group 2 (dicarboximides: e.g. iprodione and dimethachlone), Group 9 (aniline-pyrimidines: e.g. cyprodinil), and Group 12 (phenylpyrroles: e.g. fludioxonil) fungicides; there is also concern regarding Group 29 (dinitroanilines: e.g. fluazinam) fungicides. Similarly, in Australia, 7% and 9% of sclerotinia isolates were resistant to Group 1 and Group 2 fungicides, respectively. In Europe, 20-100% of isolates in some areas of France are now resistant to the Group 7 fungicide boscalid. In the US, resistance to Group 1 (thiophanate-methyl), several Group 3 (triazoles: metconazole, flutriafol, and tetraconazole), Group 7 (boscalid), and Group 11 (strobilurins: picoxystrobin) fungicides has been reported. Benomyl, a Group 1 fungicide, was de-registered in Canada and elsewhere due to development of resistance in S. sclerotiorum and many other fungal plant pathogens; Gossen et al. found similar results. In Canada, there is a big knowledge gap regarding the sensitivity of S. sclerotiorum to the fungicides currently used in canola and most other crops. Also, Canada does not have any representation on the Fungicide Resistance Action Committee. Furthermore, laboratories with expertise in fungicide resistance testing are not publicly available anywhere in Canada or in North America.
To begin addressing this deficit, the Canola Council of Canada, through the Sustainable Canadian Agricultural Partnership (SCAP) under the Canola AgriScience Research Cluster is currently funding a research project to assess the sensitivity of 400 S. sclerotiorum isolates from across the Prairie Provinces for resistance to three fungicides; boscalid (Group 7), prothioconazole (Group 3) and azoxystrobin (Group 11). Preliminary results for 114 isolates shows low levels of resistance to boscalid with only 10% of isolates having moderate levels of resistance and no isolates having high levels of resistance. Moderate levels of resistance were found to azoxystrobin in 30-70% of isolates, while high levels of resistance were found in 13% of isolates. Most worrisome, moderate to high levels of resistance to prothioconazole were found in the majority of isolates. It should be noted that how these elevated levels of resistance translate to field performance has not been established. The funding from the proposed CARP project will allow us to include another three fungicides, pydiflumetofen, fluopyram (both Group 7) and fludioxonil (Group 12), which will represent the full range of fungicides and fungicide-mixtures currently registered in Canada for control of S. sclerotiorum in canola.