Baseline sensitivity of Phytophthora capsici to the strobilurin fungicide benzothiostrobin and the efficacy of this fungicide

Abstract

Phytophthora capsici Leonian is a destructive oomycete plant pathogen that causes diseases in a wide range of crops worldwide. Benzothiostrobin is a broad-spectrum strobilurin fungicide that may control pepper Phytophthora blight. In the current study, the sensitivities of 90 P. capsici isolates collected from different regions in southern China to benzothiostrobin were measured. The curative and protective effects of benzothiostrobin against pepper Phytophthora blight were also determined. The formation of sporangia was inhibited by lower concentrations of benzothiostrobin, approximately 1 μg mL−1 on V8 media, than was necessary to inhibit zoospore discharge. The frequency distribution curve for the benzothiostrobin sensitivity was unimodal with mean EC50 values of 1.84 ± 0.24, 0.60 ± 0.10 and 4.44 ± 0.27 for inhibiting mycelial growth, sporangia formation and zoospore discharge, respectively. The P. capsici isolates used in this study exhibited decreased sensitivity to several commonly used effective fungicides, including mefenoxam, cyazofamid, fluazinam and propamocarb. Furthermore, benzothiostrobin had no cross-resistance with azoxystrobin, pyraclostrobin or famoxadone. The disease severity of pepper Phytophthora blight on pepper leaves and plants was dramatically reduced by benzothiostrobin application of 150 μg mL−1. Benzothiostrobin provided both curative and protective properties against pepper Phytophthora blight on detached pepper leaves and potted pepper plants, with greater protective activity than curative activity. These results suggested that benzothiostrobin may be used for the management of P. capsici.