Inhibitory Effect of trans-2-Hexenal Combined with Soluble Salts on Geotrichum citri-aurantii and Citrus Sour Rot Disease

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.