Regulation of Phenylpropane Metabolism and Resistance to Green Mold in Postharvest Grapefruits Treated by Carboxymethyl Chitosan-Induced Culture of Cryptococcus laurentii

The purpose of this study was to investigate the effect of carboxymethyl chitosan (CMCS)-induced culture of Cryptococcus laurentii treatment on the resistance to Penicilium italicum in postharvest grapefruits. ‘Rio Red’ grapefruits were dipped in distilled water as a control, CMCS solution, C. laurentii suspension or CMCS-induced C. laurentii suspension. The biocontrol efficacy against green mold and phenylpropane metabolism in the treated grapefruits were analyzed. The results showed that the CMCS-induced C. laurentii treatment significantly reduced the disease incidence and lesion expansion of P. italicum in grapefruits (P < 0.05). CMCS-induced C. laurentii treatment induced an increase in the activities of phenylalanine ammonia lyase (PAL), cinnamic acid 4-hydroxylase (C4H), 4-coumaric acid coenzyme A ligase (4CL), polyphenol oxidase (PPO), peroxidase (POD), β-1,3-glucanase (GLU), and chitinase (CHI), and the contents of total phenols, flavonoids and lignin compared to the control group. Therefore, CMCS can induce increased biocontrol efficacy of C. laurentii. CMCS-induced C. laurentii can enhance the resistance to Penicilium italicum in postharvest grapefruits by increasing phenolpropane metabolism and resistance substance contents, and its effect is more pronounced than those of CMCS and C. laurentii.