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Fungicide resistance in Botrytis spp. from strawberry fields in Norway

Katherine Ann Gredvig Nielsen: NIBIO / Norwegian Institute of Bioeconomy Research

<div>In 2016, Botrytis fruit rot caused unexpectedly high strawberry yield losses in southern Norway. Farmers suspected fungicide resistance in the pathogen to be a major cause, and an investigation into the presence of such resistance was thus initiated. Isolates of <em>Botrytis</em> sp. were collected from plant material in 19 strawberry fields. Resistance to boscalid, fenhexamid, fludioxonil, iprodione, pyrimethanil and pyraclostrobin were analyzed with a germination assay in 157 <em>Botrytis</em> isolates (148 for boscalid). Spores were allowed to germinate on nutrient agar amended with fungicides, and germ tube growth was recorded. We found that 89.7, 86.0, and 65.0% of the isolates were resistant to boscalid, pyraclostrobin, and fenhexamid, respectively. Moreover, 25.0% were resistant to pyrimethanil. Few isolates (2.6%) were resistant to iprodione, and none were resistant to fludioxonil. Only 8.9% of the isolates were sensitive to all the fungicides, while 5.1% were resistant to one fungicide. The remaining isolates were resistant to two (21.0%), three (43.9%), four (19.1%) and five (1.9%) fungicides. Approximately 80 % of the isolates were tested using PCR assays for mutations known to confer fenhexamid and pyraclostrobin resistance, and good correlation was observed between detected mutations and resistance phenotypes. We conclude that fungicide resistance requires consideration in practical disease management of Botrytis fruit rot in Norwegian strawberry production.</div>