Effect of ε-Poly-L-lysine on Postharvest Diseases and Disease-Resistant Substance Metabolism in Passion Fruits

In order to investigate the inhibitory effect of ε-poly-L-lysine (ε-PL) on the occurrence of Lasiodiplodia theobromae-induced diseases and its correlation with disease resistance in postharvest passion fruits, harvested golden passion fruits (cv. Fujian Baixiangguo 3) were immersed in either sterile distilled water (as control group) or 100 mg/L ε-PL solution for 10 min, inoculated with L. theobromae, and stored at (28 ± 1) ℃ and 90% relative humidity for up to 7 days. The changes of fruit lesion diameter, cell membrane permeability, lignin content and disease resistance-related enzyme activities in the pericarp were assayed every day. The results showed that compared to the control group, ε-PL delayed the increase in cell membrane permeability and lesion diameter, and enhanced the content of lignin and the activities of disease resistance-related enzymes including cinnamate-4-hydroxylase (C4H), polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL), peroxidase (POD), β-1,3-glucanase (GLU), 4-coumarate CoA ligase (4-CL), chitinase (CHI) and cinnamyl alcohol dehydrogenase (CAD), thereby maintaining cell membrane integrity by delaying the increase of cell membrane permeability, enhancing disease resistance, and inhibiting the occurrence of L. theobromae-induced diseases in harvested passion fruits.