Bioactivity, physiological characteristics and efficacy of the SDHI fungicide pydiflumetofen against Sclerotinia sclerotiorum.

Sclerotinia sclerotiorum, which can cause Sclerotinia stem rot, is a devastating plant pathogen. This study aimed to assess the potential of pydiflumetofen, a new-generation succinate dehydrogenase inhibitor (SDHI) fungicide, to control Sclerotinia stem rot. Pydiflumetofen exhibited favorable bioactivity in suppressing mycelial growth, sclerotial production and morphological changes, and the myceliogenic and carpogenic germination of sclerotia. Treatment with pydiflumetofen increased the cell membrane permeability of S. sclerotiorum and decreased oxalic acid production. In addition, inoculation tests demonstrated that the protective activity of 40 μg/mL pydiflumetofen against the fungus was better than its curative activity. Under natural infection conditions, the spraying of pydiflumetofen at 200 g a.i. ha significantly reduced the incidence and severity of Sclerotinia stem rot. In addition, the sensitivity baseline to pydiflumetofen was established using 171 isolates collected from various crops in China. The results showed that the frequency distribution of the EC values of pydiflumetofen was a unimodal curve with a mean EC value of 0.0095 ± 0.0005 μg/mL. This study confirmed the favorable bioactivity of pydiflumetofen against S. sclerotiorum at various developmental stages and its high effectiveness under natural infection conditions, which indicates that pydiflumetofen is a promising tool for the management of Sclerotinia stem rot.