We aimed to investigate the efficacy of carboxymethyl cellulose (CMC) in inducing C. laurentii to antagonize postharvest penicillium (Penicillium expansum) and green mold (Penicillium digitatum) in ‘Shatangju’ mandarin. In this study, the culture time of C. laurentii induced by 0.5% CMC (mass fraction) was optimized for improved antagonistic effect against blue and green mold in commercially available ‘Shatangju’ mandarin. Using sterile water as a control, the effect of C. laurentii cultures induced and not induced by 0.5% CMC on the resistance to blue and green mold, the induction of disease defense system formation and the storage quality of ‘Shatangju’ mandarin was explored. The results showed that the optimal induction time for C. laurentii against both molds was 72 h. The biocontrol of C. laurentii against the two molds was significantly better at 72 h than at other induction times (P < 0.05). C. laurentii induced by 0.5% CMC for 72 h significantly inhibited the incidence and lesion diameter of blue and green mold (P < 0.05). In addition, it increased the activities of β-1,3-glucanase, chitinase, phenylalamine ammonia lyase and polyphenoloxidase and the contents of total phenols and flavonoids in citrus fruit on the eighth day of storage compared to the control group, thereby maintaining the nutritional quality of‘Shatangju’ mandarin during storage. Accordingly, it was concluded that the addition of 0.5% CMC to the culture medium can improve the biocontrol efficacy of C. laurentii. The CMC-induced culture of C. laurentii can increase disease defenserelated enzyme activities, promote the synthesis and accumulation of antioxidant substances in ‘Shatangju’ mandarin, inhibit the occurrence of postharvest blue and green mold, and consequently maintain the storage quality of the fruit.

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.

The hardness of ‘Rio Red’ grapefruits treated postharvest with carboxymethyl chitosan (CMCS), Cryptococcus laurentii or C. laurentii induced by CMCS was measured during storage. The results showed that compared with the control group (treatment with sterile water), CMCS-C. laurentii treatment significantly maintained the firmness of grapefruits during storage (P < 0.05). Moreover, fruit mass loss percentage and the polysaccharide content and polysaccharide hydrolase activity of the cell wall were measured and cell wall microstructure was observed during storage for 75 days. The results indicated that CMCS-C. laurentii treatment was effective in maintaining the contents of sodium carbonate soluble pectin (SCSP) and 24% KOH-soluble fraction (24KSF) and reducing the contents of water-soluble pectin (WSP), ionic-soluble pectin (ISP) and 4% KOH-soluble fraction (4KSF) in the fruit. Compared with the control group, the activities of the cell wall-degrading enzymes pectin methylesterase (PE), polygalacturonase (PG), cellulase (CX), α-L-arabinofuranosidase (α-L-Af) and β-galactosidase (β-Gal) were significantly inhibited by CMCS-C. laurentii treatment. In the middle and later stages of storage, the cell wall structure of the fruit treated with CMCS-C. laurentii was more stable and the intracellular structure was relatively intact. In conclusion, CMCS-C. laurentii treatment can slow down the degradation of organelles and cell walls in postharvest grapefruits, maintain cell integrity better and delay fruit softening.

To study the effect of 6’-O-caffeoylarbutin (CA) treatment on the prevention and control of gray mold in postharvest blueberry fruit and its effect on fruit phenylpropane metabolism, blueberries were soaked in 2.5 mmol/L CA solution or distilled water as the control. The results showed that CA treatment significantly reduced the incidence of gray mold in postharvest blueberry fruit and inhibited the expansion of lesion diameter when compared with the control. Meanwhile, it increased the activities of phenylalanine ammoniase (PAL), cinnamic acid-4-hydroxylase (C4H), 4-coenzyme coenzyme A ligase (4CL), cinnamyl alcohol dehydrogenase (CAD), polyphenol oxidase (PPO) and peroxidase (POD), as well as the contents of total phenols, flavonoids and lignin, with few adverse effects on the storage quality. It is concluded that CA treatment could promote the synthesis and accumulation of resistance-related substances and consequently enhance the resistance to gray mold by activating the enzyme activities related to phenylpropane metabolism in postharvest blueberry fruit.