Application of Pullulan to Induce Disease Resistance Against Diaporthe nobilis in Postharvest Kiwifruit

Kiwifruit stands out as a globally favored fruit owing to its palatable flavor and nutritional benefits. However, it continues to ripen after harvest, and this trait makes it more susceptible to fungal infections. Diaporthe spp. has garnered attention for causing postharvest soft rot in kiwifruit; consequently, effective prevention and treatment strategies for soft rot are crucial for managing postharvest diseases in kiwifruit. We found that pullulan treatment greatly decreased both the incidence of disease and lesion diameter following Diaporthe nobilis inoculation in kiwifruit. Pullulan at the concentrations (1%, 3%, and 5%) markedly reduced the disease incidence of the soft rot in kiwifruit after 3 days of inoculation with D. nobilis by 19.16%, 31.66%, and 48.33%, respectively, and lesion diameter of 5% pullulan treated kiwifruit was 38.1% lower than that of the control 3 days after treatment. Importantly, pullulan treatment maintained and reduced the accumulation of superoxide anion (O₂⁻), hydrogen peroxide (H₂O₂), and the peroxidation of membrane lipids; maintained high levels of ascorbic acid (AsA) and glutathione (GSH); and stimulated the buildup of total phenolic. Additionally, pullulan treatment markedly increased the activities of defense-related enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), phenylalanine ammonialyase (PAL), chitinase (CHI), and β-1,3 glucanase (GLU). Furthermore, pullulan treatment was found to activate expressions of defense-related genes. Overall, our data confirm the application of pullulan treatment for controlling postharvest soft rot in kiwifruit, potentially offering a valuable strategy for enhancing the storage stability and shelf life of this economically significant fruit.