Sodium Cuminate Inhibits the Mycelial Growth of Penicillium digitatum by Inducing Oxidative Stress and Damaging the Cell Membrane

Green mold formed by Penicillium digitatum is a major disease that limits the yield and overall value of postharvest citrus fruits. The antifungal activity of sodium cuminate (SC) against P. digitatum and the corresponding mechanism were explored in this research. The minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) of SC against P. digitatum were 0.4 and 0.8 g L−1, respectively. SC (8 × MFC) reduced the incidence of disease in Ponkan fruits without compromising their quality. The results of CFW staining and extracellular alkaline phosphatase assays revealed that 1/2MIC SC for 30 min had no impact on the cell wall integrity of P. digitatum. In contrast, 1/2MIC SC apparently destroyed cell membrane integrity, as shown by the increase in the content of reactive oxygen species (ROS), malondialdehyde, and H2O2. The addition of exogenous cysteine (Cys) or diphenyleneiodonium chloride (DPI) significantly mitigated the cytotoxic effects of SC. At the same time, mitochondrial membrane potential was significantly decreased by 1/2MIC SC, and the addition of exogenous Cys or DPI restored it to normal levels. In summary, the antifungal capacity of SC might be attributable to membrane damage in P. digitatum caused by oxidative stress.