Risk Evaluation of Benzovindiflupyr Resistance of Verticillium dahliae Population in Maine

causes Verticillium wilt, resulting in significant losses to potato production. Benzovindiflupyr, a succinate dehydrogenase inhibitor, effectively controls . However, frequent applications of the chemical may expedite the development of fungicide resistance in the pathogen population. To evaluate the risk of benzovindiflupyr resistance, 38 strains were obtained from diseased potatoes in Maine. The sensitivity of the field population was determined based on effective concentration for 50% inhibition (EC ), which ranged from 0.07 to 11.28 μg ml with a median of 1.08. Segregated clusters of EC values indicated that Maine populations have developed benzovindiflupyr resistance. By exposing conidia of to a high concentration of benzovindiflupyr, 18 benzovindiflupyr-resistant mutants were obtained. To examine their fitness, the mutants were continuously subculture-transferred for up to 10 generations. Mycelial growth, conidial production, competitiveness, pathogenicity, and cross resistance of the 10th generation mutants were examined. Results showed that 50% of the resistant mutants retained an adaptive level in mycelial growth, and 60% maintained conidial production similar to their parents. Pathogenicity did not change for any of the mutants. No cross resistance was detected between benzovindiflupyr and either azoxystrobin, boscalid, fluopyram, or pyrimethanil. Thus, the resistance risk in to benzovindiflupyr should be considered in Maine potato production.