Molecular Characterization of Botrytis Isolates from Blueberry and Red Raspberry in the Pacific Northwest with Resistance to SDHI Fungicides

Botrytis cinerea, a high-risk pathogen for fungicide resistance development, poses a significant threat to yield and fruit quality of blueberry and red raspberry in the Pacific Northwest. Succinate dehydrogenase inhibitor (SDHI) fungicides are effective botryticides that are considered medium to high risk for resistance development. Analysis of sdhB sequences from Botrytis isolates (n = 278) exhibiting different levels of sensitivity to any of four SDHIs (boscalid, fluxapyroxad, fluopyram, and isofetamid) revealed six previously characterized mutations in 244 isolates: N230I, P225F, H272R, H272V, H272Y, and I274V, at frequencies of 40, 22, 22, 10, 5, and 1%, respectively. Different mutations in the sdhB gene resulted in twelve phenotypic profiles exhibiting in vitro resistance to the four SDHIs. In contrast, sdhC and sdhD sequences revealed no consistent mutations linked to a specific fungicide resistance profile. Importantly, among the mutations in sdhB, 72% were P225F, H272V, or N230I, which confer cross-resistance to multiple SDHI fungicides. These findings emphasize the need for balanced use and rotation of fungicides to manage Botrytis effectively in blueberry and red raspberry fields in the Pacific Northwest.