Abstract
Chitosan is an elicitor that induces resistance in fruits against postharvest diseases, but there is little knowledge about the wound healing ability of chitosan on apple fruits. Our study aimed at revealing the effect of chitosan on the phenylpropanoid pathway by determining some enzyme activities, products metabolites, polyphenol oxidase activity, color (L*, b*, a*), weight loss, and disease index during healing. Apple (cv. Fuji) fruits wounded artificially were treated with 2.5% chitosan and healed at 21–25°C, relative humidity = 81–85% for 7 days, and non-wounded fruits (coated and non-coated) were used as control. The result shows that chitosan treatment significantly decreased weight loss of wounded fruits and disease index of Penicillium expansum inoculated fruits. The activities of phenylalanine ammonia-lyase (PAL), cinnamic acid 4-hydroxylase (C4H), 4-coumaryl coenzyme A ligase (4CL), cinnamoyl-CoA reductase (CCR), and cinnamyl alcohol dehydrogenase (CAD) were elicited throughout the healing period by chitosan, which increased the biosynthesis of cinnamic acid, caffeic acid, ferulic acid, sinapic acid, p-coumaric acid, p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. Also, total phenol, flavonoid, and lignin contents were significantly increased at the fruits wounds. In addition, chitosan’s ability to enhance polyphenol oxidase activity stimulated enzymatic browning of wounds. Although wounding increased phenylpropanoid enzymes activities before healing, chitosan caused higher enzyme activities for a significant healing effect compared with the control. These findings imply that chitosan accelerates apple wound healing by activating the phenylpropanoid pathway and stimulating enzymatic browning of wounds.
Highlights
Apple (Malus domestica Borkh.) is the most economically widely produced fruit crop in temperate zones (Wang et al, 2018)
Chitosan induced resistance to anthracnose caused by Colletotrichum gloeosporioides in citrus (Zhao et al, 2018), blue mold caused by Penicillium expansum in apples (Lu et al, 2014; Li et al, 2015), and green and blue mold caused by Penicillium digitatum and Penicillium italicum in orange (Zeng et al, 2010)
On day 7, the weight loss of wounded chitosantreated fruits was lower by 43% when compared with that of the control, but there was no significant difference compared with the non-wounded control (Figure 1A)
Summary
Apple (Malus domestica Borkh.) is the most economically widely produced fruit crop in temperate zones (Wang et al, 2018). Chitosan is a chitin N-deacetylated derivative obtained from crustaceans’ outer shells, mainly shrimps, crabs, krills, some fungi cell walls, etc It is a natural polymer with a polycationic nature, non-toxic, biodegradable, excellent film-forming property, and antimicrobial effect (Deepmala et al, 2014; Silva and Pighinelli, 2017). Chitosan is used as an elicitor to induce resistance against postharvest diseases of horticultural crops (Romanazzi et al, 2017), such as gray mold caused by Botrytis cinerea in tomatoes, grapes, strawberries, apples, and peaches (Plainsirichai et al, 2014; Zhang et al, 2015; Gayed et al, 2017; Peian et al, 2021). The recent work by our team reveals that preharvest spraying with chitosan accelerated the wound healing process of muskmelons after harvesting by eliciting phenylpropanoid metabolism for the production of phenolic compounds and lignin at the wounded site (Li et al, 2021). The (1) weight loss of wounded/non-wounded fruits and disease index of P. expansum inoculated fruits were evaluated, (2) some important enzyme activities and products metabolites were determined, and (3) PPO activity and color (L∗, b∗, a∗) of wounds during healing were subsequently analyzed
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