Resistance risk and resistance-associated point mutations in the target protein PcVHA-a of fluopimomide in Phytophthora capsici

Abstract

Fluopimomide, developed by Shandong Sino-Agri United Biotechnology Co., Ltd., is a pyridinylmethyl-benzamide fungicide with good activity against plant diseases caused by phytopathogenic oomycetes. However, there is uncertainty surrounding the resistance risk of fluopimomide and its resistance mechanism in Phytophthora capsici. In this study, the baseline sensitivity of P. capsici to fluopimomide was established, and 106 P. capsici isolates shown sensitive to fluopimomide, with a mean EC50 value of 5.1892 ± 2.2613 μg/mL. Fungicide adaptation produced three fluopimomide-resistant P. capsici mutants, two of which exhibited considerably lower compound fitness index (CFI) than the parent strain, and one showed significantly improved CFI. While cross-resistance was observed between fluopimomide and fluopicolide, no cross-resistance was detected between fluopimomide and other fungicides. Overall, P. capsici presents a moderate resistance risk to fluopimomide. Two point mutations, G767E and K847R, were identified in the V-ATPase subunit a of P. capsici (PcVHA-a) in resistant mutants. These mutations were subsequently validated through site-directed mutagenesis and molecular docking assays, confirming their roles in conferring fluopimomide resistance in P. capsici.