Baseline Sensitivity and Control Efficacy of Strobilurin Fungicide Pyraclostrobin Against Sclerotium rolfsii

Sclerotium rolfsii is a fungi pathogen of southern blight with broad host range. The quinone outside inhibitor fungicide pyraclostrobin was officially approved for controlling many diseases in 2015. In this study, baseline sensitivity of S. rolfsii to pyraclostrobin was established by measuring the 50% effective concentration (EC₅₀) values of 155 isolates of S. rolfsii. The EC₅₀ values ranged from 0.0291 to 1.0871 µg/ml, with a mean EC₅₀ of 0.4469 ± 0.2490 µg/ml (mean ± standard deviation). In a preventive fungicide in vitro experiment and a field experiment, pyraclostrobin preventive efficacy reached 90% and 80%, respectively, which were much higher than that of the control agent carbendazim. Curative efficacy of pyraclostrobin was significantly lower than its preventive efficacy. Pyraclostrobin at 0.1, 0.5, and 2 μg/ml significantly reduced the number of sclerotia produced on potato dextrose agar medium, but had no significant influence on their total weight. Pyraclostrobin had no significant influence on mycelial cell membrane permeability, but it significantly reduced oxalate secretion and protein synthesis of S. rolfsii. Our findings are of great significance for resistance monitoring of S. rolfsii and also provide new insight into the action mechanism of pyraclostrobin against S. rolfsii.