Fungicide resistance in Botrytis cinerea and identification of Botrytis species associated with blueberry in Michigan

Botrytis blossom blight and fruit rot, caused by Botrytis cinerea, is a significant threat to blueberries, potentially resulting in substantial economic losses if not effectively managed. Despite the recommendation of various cultural and chemical practices to control this pathogen, there are widespread reports of fungicide resistance, leading to decreased efficacy. This study aimed to characterize the resistance profile of B. cinerea isolated from blighted blossoms and fruit in 2019, 2020 and 2022 (n = 131, 40, and 37 for the respective years). Eight fungicides (fludioxonil, thiabendazole, pyraclostrobin, boscalid, fluopyram, fenhexamid, iprodione, and cyprodinil) were tested using conidial germination at specific discriminatory doses. Additionally, 86 isolates were phylogenetically characterized using the internal transcribed spacer regions (ITS) and the protein coding genes: glyceraldehyde-3-phosphate dehydrogenase (G3PDH), heat-shock protein 60 (HSP60), and RNA polymerase II second largest subunit (RPB2). This revealed higher fungicide resistance frequencies in 2020 and 2022 compared to 2019. Over all 3 years, over 80% of the isolates were sensitive to fludioxonil, fluopyram, and fenhexamid. Pyraclostrobin and boscalid showed the lowest sensitivity frequencies (