Risk evaluation of Benzovindiflupyr resistance of Verticillium dahliae population in Maine

Authors: LI, K. - University Of Maine; WANG, Y. - Jilin University; GE, T. - University Of Maine; Larkin, Robert - Bob; SMART, A. - University Of Maine; JOHNSON, S. - University Of Maine; HAO, J. - University Of Maine

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2022
Publication Date: 3/19/2023
Citation: Li, K., Wang, Y., Ge, T., Larkin, R.P., Smart, A., Johnson, S.B., Hao, J. 2023. Risk evaluation of Benzovindiflupyr resistance of Verticillium dahliae population in Maine. Plant Disease. https://doi.org/10.1094/PDIS-06-22-1384-RE.
DOI: https://doi.org/10.1094/PDIS-06-22-1384-RE

Interpretive Summary: Verticillium wilt, caused by the fungus Verticillium dahliae, is a persistent soilborne disease that causes significant losses in potato production. The disease can often be effectively managed using the chemical fungicide benzovindiflupyr. However, frequent applications of the fungicide may lead to the development of resistance to the fungicide within the pathogen population, rendering the fungicide no longer effective. To evaluate the risk of benzovindiflupyr resistance in V. dahliae in Maine, 38 V. dahliae strains were obtained from diseased potatoes. Sensitivity assessments to benzovindiflupyr indicated that V. dahliae has developed benzovindiflupyr resistance in field populations in Maine. The fitness of numerous benzovindiflupyr-resistant mutants were examined regarding mycelial growth, conidial production, competitiveness, pathogenicity, and cross-resistance. Results showed that more than 50% of the resistant mutants retained comparable fitness traits to their parents after numerous growth generations. No mutants had pathogenicity changed. No cross resistance was detected between benzovindiflupyr and several other fungicides, including azoxystrobin, boscalid, fluopyram, or pyrimethanil. Thus, there is substantial risk for development of benzovindiflupyr resistance in V.dahliae in Maine, and requires rotation of fungicides used for effective management of this pathogen in potato production. This research is useful for scientists, extension personnel, and growers, providing information on the effective use of fungicides in the management of verticillium wilt and the risk for development of fungicide resistance.

Technical Abstract: Verticillium dahliae causes Verticillium wilt resulting in significant losses to potato production. Benzovindiflupyr, a succinate dehydrogenase inhibitor (SDHI), effectively controls V. dahliae. However, frequent applications of the chemical may expedite the development of fungicide resistance in the pathogen. To evaluate the risk of benzovindiflupyr resistance, 38 V. dahliae strains were obtained from diseased potatoes in Maine. The sensitivity of the field population was determined based on effective concentration for 50% inhibition (EC50), which ranged from 0.07 to 11.28 µg ml/1 with a median of 1.08. Segregated clusters of EC50 values indicated that V. dahliae has developed benzovindiflupyr resistance in field populations. By exposing conidia of V. dahliae to a high concentration of benzovindiflupyr, 18 benzovindiflupyr-resistant mutants were obtained. To examine their fitness, the mutants were continuously transferred for up to ten 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%