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Sensitivity and resistant management for the SDHI fungicide fluxapyroxad in the apple scab pathogen Venturia inaequalis
Katrin Ayer: Cornell University; Kerik Cox: Cornell University; Sara Villani: North Carolina State University
<div>The recent registration of the SDHI fungicide fluxapyroxad for apple scab management prompted investigations into the sensitivity of <i>Venturia</i> <i>inaequalis </i>and fungicide application practices. Baseline isolates of <i>V. inaequalis </i>were used to determine the effective concentration of fluxapyroxad at which conidial germination and mycelial growth was inhibited by 50% (EC<sub>50</sub>). Mean EC<sub>50</sub> values for fluxapyroxad conidial and mycelial growth were 0.028 and 0.25 μg ml<sup>-1</sup>, respectively. Using a draft genome of <i>V. inaequalis</i>, the <i>sdhC</i> and <i>sdhD </i>genes were identified and characterized to compliment the previously characterized <i>sdhB </i>gene. Translated proteins had > 60% identity with <i>sdhC</i> and <i>sdhD </i>genes from other fungi. This baseline sensitivity and genetic information will serve as the foundation for phenotyping and genotyping SDHI sensitivity in populations<i> </i>of <i>V. inaequalis</i>. To evaluate fungicide application practices for resistance management, field experiments at two research orchards using commercial fluxapyroxad products (Sercadis® and Merivon®) were performed using both low and high application rates as well as a combination with single-site with multi-site fungicides. In the first year, few significant differences were observed between treatments at both locations. However, plots left untreated and those treated with Merivon had populations with the highest sensitivity to fluxapyroxad. Repeated experiments in subsequent years may lead to an improved evaluation of application practices for resistance management.</div>

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