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

<i>Botrytis cinerea</i>, 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 <i>sdhB</i> sequences from <i>Botrytis</i> isolates (<i>n</i> = 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 <i>sdhB</i> gene resulted in 12 phenotypic profiles exhibiting in vitro resistance to the four SDHIs. In contrast, <i>sdhC</i> and <i>sdhD</i> sequences revealed no consistent mutations linked to a specific fungicide resistance profile. Importantly, among the mutations in <i>sdhB</i>, 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 <i>Botrytis</i> effectively in blueberry and red raspberry fields in the Pacific Northwest.