This study explored the inhibitory effect and potential antifungal mechanism of α-terpineol against an imazalil-resistant strain of Penicillium digitatum Pdw03. In vitro experiment showed that α-terpineol exhibited antifungal activity against P. digitatum Pdw03, with minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of 4.00 μL/mL. In vivo results showed that α-terpineol at MFC and 5 MFC significantly reduced the incidence of green mold and lesion diameter in ponkan fruit inoculated with P. digitatum Pdw03. Propidium iodide (PI) staining indicated that 1/2 MIC α-terpineol evidently decreased the cell membrane integrity, ergosterol content (P < 0.05) and gene expression of squalene synthase (ERG9) (P < 0.05) in P. digitatum Pdw03. These results suggest that α-terpineol affects the growth of P. digitatum Pdw03 by inhibiting the gene expression of ERG9, and thus is an effective alternative for controlling postharvest citrus diseases.

Sour rot disease, caused by Geotrichum citri-aurantii, is one of the major postharvest diseases of citrus. In this study, the inhibitory effect of trans-2-hexenal combined with soluble salts on G. citri-aurantii and sour rot disease was investigated through in vitro and in vivo experiments. Results showed that sodium phosphate had a strong antifungal activity against G. citri-aurantii, with minimal inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of 4.00 and 16.00 mg/mL, respectively, whereas sodium diacetate had relatively poor inhibitory effect, with both MIC and MFC of 16.00 mg/mL. However, the growth of G. citri-aurantii could not be completely inhibited by calcium propionate at 16.00 mg/mL. The in vitro experiments showed that the combination of trans-2-hexenal with sodium phosphate, sodium diacetate or calcium propionate resulted in a synergistic effect, with both MIC and MFC of 0.23 mg/mL. When trans-2-hexenal was combined with sodium dehydroacetate, it resulted in an additive effect, with both MIC and MFC of 0.46 mg/mL. The in vivo experiments showed that the combination of trans-2-hexenal at 5 × MFC and 10 × MFC with sodium dehydroacetate had the best inhibitory effect on the development of sour rot disease in citrus fruit inoculated with G. citri-aurantii, and the incidence rate was 0% after six days, which was significantly lower than that observed in the control group (100%). The combination of trans-2- hexenal and sodium dehydroacetate can effectively inhibit the growth of G. citri-aurantii and reduce the incidence of sour rot disease of citrus.