Trans-2-hexenal inhibits the growth of imazalil-resistant Penicillium digitatum Pdw03 and delays green mold in postharvest citrus

This study investigated the efficacy of trans-2-hexenal in preventing green mold on postharvest citrus fruit and its mode of action against imazalil-resistant Penicillium digitatum Pdw03. Trans-2-hexenal inhibited Pdw03 at a minimum inhibitory concentration (MIC) and a minimum fungicidal concentration (MFC) of 0.25 mL L−1. Trans-2-hexenal reduced the incidence of green mold, which is a plant volatile compound with potent antifungal properties. Ultrastructural analysis revealed that trans-2-hexenal altered the mitochondrial structure of Pdw03. Trans-2-hexenal also increased the amount of reactive oxygen species, which hindered mitochondrial energy metabolism of Pdw03, resulting in mitochondrial structural damage and malfunction, and a decrease in mitochondrial membrane potential. In addition, RNA-seq analysis revealed that trans-2-hexenal altered the expression of some energy metabolism genes associated with the tricarboxylic acid (TCA) cycle, glycolysis, and oxidative phosphorylation of Pdw03. Superoxide dismutase, catalase, glutathione S-transferase, and glutathione peroxidase activities were altered, and expression of the relevant gene was also quantified by real-time fluorescence quantitative PCR. Trans-2-hexenal damaged ribosomes, primarily by downregulation of the ribosomal structural component-associated genes RPL3, RPS18, RPL12, RPL26, RPL13A, RPL9, RPL23, and RPL4, and then by reducing protein synthesis to achieve the inhibitory effect.