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The advent and spread of prodigious multi-fungicide resistance in Botrytis cinerea
Guido Schnabel: Clemson University; Matthias Hahn: Department of Biology, University of Kaiserslautern; Natalia Peres: Gulf Coast Research and Education Center; University of Florida; Mengjun Hu: Clemson University
<div><span face="Calibri" style="font-family:Calibri;" size="3">Of all fungal plant pathogens, Botrytis cinerea is perhaps the most capable of developing fungicide resistance. This causal agent causes gray mold disease on dozens of ornamentals, vegetables, and fruits worldwide. Over the last six years we have been monitoring strawberry fields in the eastern Unites States and reported simultaneous chemical class resistance (CCR) to up to 7 different classes of fungicides. Genetic analysis revealed that resistance is mostly qualitative in nature and based on point mutations in target genes. In contrast, resistance to fludioxonil is primarily based on Mrr1 transcriptional activator-driven overexpression of the drug efflux pump AtrB. Multiyear resistance screening revealed at first an increase in CCR that was aided at least in part by ‘selection by association’ where fungicide resistance traits were likely linked to the trait being selected rather than being the selected trait itself. But in recent years the frequency of multi-CCR isolates in strawberry populations has stabilized. This stabilization may be due to recent efforts to implement resistance management on the nursery level, the implementation of location-specific resistance management practices, and the recently described impairment of multi-CCR isolates to compete with sensitive isolates. The newly discovered species Botrytis fragariae is a frequent colonizer of strawberry flowers in Europe and the USA and multifungicide resistance in this pathogen is also ubiquitous. However, the role of B. fragariae in pre- and postharvest fruit rot is still unclear. </span></p> <p><span size="3"> </span></div>

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