Preharvest Chitosan Treatments Promote Wound Healing And Maintain Quality Of Postharvest Potato Tubers

Wound healing is a typical reaction of potato tuber after being damaged,but completely natural healing of tubers needs a longer time,which easily leads to tuber rot and quality deterioration.Therefore,it is necessary to take measures to promote healing of tubers.In this study,potato cultivar "Longshu 7" original seeds were taken as material.The tubers were soaked with 2% chitosan(soaking),and foliar spraying at seedling stage,tuber period and 1week before harvest.The effect of preharvest treatments on harvested tuber healing was evaluated by measuring weight loss of wounded tubers and the incidence of inoculated tubers.The accumulation of suberin polyphenolic(SPP),suberin polyaliphatic(SPA)and lignin were observed at the wounded sites.The activity of the key enzymes and the content of substances of the phenylpropane pathway were determined,also the activity of peroxidase(POD)and polyphenol oxidase(PPO).And the effect of chitosan preharvest sprays was evaluated on the growth of plants and the quality of tuber during storage.The results showed as below:1.Preharvest chitosan treatments effectively inhibited the weight loss of the wouned tubers and the decay incidence of inoculated tubers during healing,the treatment of soaking +spraying showed the best,then the spraying.The weight loss of the wounded tubers treated with soaking + spraying,spraying and soaking was 51.1%,44.7% and 37.6% of higher than the control after 14 days of healing.The decay incidence of inoculated tubers treated with soaking + spraying,spraying and soaking was 71.1%,60.7% and 55.3% of higher than the control after 5 days of healing.The results of weight loss and incidence indicated that chitosan preharvest treatments effectively promote wound healing of potato tubers,and shorten healing time.2.Preharvest chitosan treatments promoted the accumulation of SPP,SPA and lignin at the wounded sites during the healing of tubers,the treatment of soaking + spraying showed the best,then the spraying.The accumulation results of SPP,SPA and lignin at wounded sites indicated that chitosan preharvest treatments induced the rapid formation of tuber healing structure tissue.3.Chitosan treatments increased the activity of phenylalanine ammonia lyase,cinnamic acid hydroxylase,4-coumaryl coenzyme A-ligase and cinnamyl alcohol dehydrogenase at the wound sites of the tuber during the healing of tubers.The activity of phenylalanine ammonia lyase of tubers treated with soaking + spraying,spraying and soaking was 54.1%,43.7% and 39.8% of higher than the control after 7 days of healing.The treatments also enhanced the content of the total phenolics,flavonoid and lignin at the wound sites of thetubers.The total phenolics content of the tubers treated with soaking + spraying,spraying and soaking was 54.1%,43.7% and 39.8% of higher than the control after 7 days of healing.It is suggested that preharvest chitosan treatments active the phenylpropane pathway of harvested potato tubers..4.Chitosan enhanced the activity of POD and PPO at the wound sites of the treated tubers.The POD activity of tubers treated with soaking + spraying,spraying and soaking was61.75%、24.79% and 35.8% of higher than the control after 14 days of healing.The activity increase results indicated that POD and PPO improve oxidation and crosslinking of healing substances of tubers.5.Preharvest treatments increased the stem height and stem diameter of potato plants.However,the treatments had no obviously effect on the yield of tuber.The treatments also maintained the content of starch,crude protein and reducing sugar of the tuber.It is suggested that preharvest chitosan treatments induce phenylpropane pathway,increase oxidase activity,improve the accumulation of SPP,SPA and lignin at the wound sites,effectively reduce weight loss and incidence of tubers,and shorten the healing time.The treatment of soaking + spraying shows the best effect for wound healing of harvested potato tubers.