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Poster: Biology & Disease Mgmt: Chemical Control


Baseline sensitivities to SDHI fungicides and characterization of the sdhB gene in Venturia inaequalis
S. VILLANI (1), K. Ayer (2), K. Cox (2) (1) North Carolina State University, U.S.A.; (2) Cornell University, U.S.A.

The succinate dehydrogenase inhibitor (SDHI) fungicides are a class of broad spectrum, single-site fungicides that interfere with fungal respiration in the mitochondrion. The recent registration of next-generation SDHIs for apple scab management prompted an investigation into the baseline sensitivity of Venturia inaequalis to penthiopyrad, fluopyram, and benzovindiflupyr. Thirty-five to 70 isolates with no prior exposure to single-site fungicides were used to determine the effective concentration at which conidial germination was inhibited by 50% (EC50). Mean EC50 values for penthiopyrad, fluopyram, and benzovindiflupyr were 0.086, 0.176 and 0.0016 μg ml-1, respectively. Linear correlation analysis revealed a significant and positive correlation in sensitivity between fluopyram and penthiopyrad (P ≤ 0.0001, r = 0.66) and fluopyram and benzovindiflupyr (P = 0.0014, r = 0.52). Genomic sequencing was performed using the Illumina MiSeq platform to identify and characterize the sdhB gene for 3 isolates collected from a research, baseline, and commercial orchard population. No common mutation sites commonly associated with SDHI resistance were discovered in these isolates, or in other isolates that were recovered following field applications of SDHIs. Results suggest that SDHIs are highly effective against conidial germination and provide a basis for phenotypic and genotypic monitoring of SDHI resistance in populations of V. inaequalis.