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POSTERS: Fungicide and antibiotic resistance

Fungicide resistance in Penicillium expansum from pome fruit in the U.S. Pacific Northwest
Achour Amiri - Washington State University. Laxmi Pandit- Washington State University

Blue mold caused by Penicillium expansum and Penicillium spp. is the most important postharvest pathogen of apple and pear in the U.S. Pacific Northwest and worldwide. Its management is achieved through sanitation and application of fungicides, from three chemical groups, i.e. methyl-benzimidazole carbamate (MBC), phenylpyrrole (PP), and anilinopyrimidine (AP), applied at harvest. We conducted two years of fungicide resistance monitoring and assessed the sensitivity of more than 6,000 P. expansum isolates to the MBC-thiabendazole (TBZ), the PP-fludioxonil (FDL), and the AP-pyrimethanil (PYR). Sensitivity was assessed using germination and germ tube length on agar media amended with discriminatory doses of each fungicide. Overall, resistance frequencies ranged from 15% to 45% for TBZ and 12 to 40% for PYR. About 5 to 12% or isolates tested showed reduced sensitivity to FDL. The majority (80%) of the isolates tested was either sensitive to all fungicides or resistant to one fungicide only. Our results indicate that the three postharvest fungicides can still be part of the overall disease management program including as long as they are rotated yearly. However, because pome fruit are stored for up to a year, further investigation is needed to ensure that the relatively low resistance frequencies observed do no cause a significant reduction in the efficacy of fungicides over the long storage period.