Antifungal mechanisms of Phoebe bournei wood essential oil against Botryosphaeria dothidea and its application in apples

The high susceptibility of apple fruit to Botryosphaeria dothidea severely limits their postharvest storage. Phoebe bournei essential oil has shown antimicrobial activity against microorganisms. However, its antiphytopathogenic fungal properties and mechanisms have not been thoroughly investigated.The study showed that Phoebe bournei wood essential oil (PWEO) had strong antifungal activity on B. dothidea and could effectively inhibit apple postharvest ring rot. Microscopic observation revealed that PWEO treatment significantly damaged the morphological structure of B. dothidea . PWEO compromised the integrity of the fungal cell membranes, leading to an increase in extracellular nucleic acids, proteins, and electrical conductivity, as confirmed by PI staining. Prolonged PWEO treatment led to a decrease in total lipid, ergostero and trehalose content but an increase in glycerol content. Fluorescent dye staining revealed that PWEO induced intracellular reactive oxygen species (ROS) accumulation leading to lipid peroxidation and mitochondrial membrane potential (MMP) disruption. PWEO also increased four antioxidant enzyme activities in apples. The weighted gene co-expression network analysis (WGCNA) analysis was used to screen out the genes associated with the physiological indexes as differential genes and quantitatively verified, and the results showed that PWEO significantly up-regulated the expression of glycoside hydrolase ( GH16 ), while down-regulating the expression of Chitin synthetase ( CHS ), β-1,3-glucan synthase ( FKS ), ergosterol synthase ( ERG28 ), multidrug-resistance-like protein B ( MdlB ), and superoxide dismutase ( SOD1 ) in B. dothidea . GC-MS analysis revealed that composition of PWEO was significantly different from the EOs of other tissues of P. bournei , and demonstrated that (-)-borneol, isoborneol, terpinen-4-ol, guiazulene and o -cymene contributed to the antifungal activity of PWEO. In summary, PWEO is a promising antifungal agent for controlling apple postharvest ring rot.