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

Green mold formed by <i>Penicillium digitatum</i> is a major disease that limits the yield and overall value of postharvest citrus fruits. The antifungal activity of sodium cuminate (SC) against <i>P. digitatum</i> and the corresponding mechanism were explored in this research. The minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) of SC against <i>P. digitatum</i> 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 <i>P. digitatum</i>. 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 <i>P. digitatum</i> caused by oxidative stress.