Fungicide Resistance in Botrytis spp. Isolates from Northeast and California Strawberry Fields

Botrytis fruit rot is a major disease affecting strawberry production worldwide, involving several species. In this study, 1,222 isolates were collected from California and Northeastern U.S. strawberry fields to analyze their resistance phenotypes and genotypes. High frequencies of resistance were detected to thiophanate-methyl and pyraclostrobin, whereas lower but increasing frequencies were found to newer fungicides such as succinate dehydrogenase inhibitors (SDHIs). Botrytis isolates from California strawberry fields showed higher resistance frequencies than those from Northeastern states, and isolates from New York exhibited the lowest levels among all states tested. Higher chemical class resistance (CCR) was observed in isolates collected from plasticulture strawberries compared with matted-row strawberries, with 5CCR and 3CCR as the most common phenotypes, respectively. B. cinerea was found to be the major species involved, followed by B. fragariae and B. caroliniana. Although resistance mechanisms are largely shared across the species, B. fragariae exhibited higher frequencies of resistance to fludioxonil, whereas little or no resistance was detected to fenhexamid and SDHIs. Analysis of mrr1 sequences revealed various mutations associated with fludioxonil-resistant phenotypes, with six mutations previously undescribed. Further, N230I in sdhB was found to be the most prevalent mutation responsible for SDHI resistance.