Research On Physiological And Ecological Mechanism Of Peel Browning Of ’Ruixue’ Apple Induced By Bagging

‘Ruixue’ is a new apple variety selected by Northwest A & F University.‘Ruixue’fruits are of excellent qualities,but it is prone to appear physiological browning during the bagging cultivation process,which seriously affects the commercial value.The research explored the sensitivity differences among different apple varieties to the microenvironment of fruit bags;Non-bagging ‘Ruixue’ fruits used as a control,this research compared the differences in the microenvironment,physiological active substances,the structure of peel wax and cell tissue in the fruits between non-bagging and bagging,which aimed to explore the ecological conditions of bagging-induced peel browning in ‘Ruixue’ apples,and analyzed the effects of mechanisms of enzymatic browning;On this basis,we changed the micro-environment of bagging fruits by debagging,which relieved the peel browning of ‘Ruixue’ apples.The research acquired were as below:1.Peel browning of apple caused by bagging is a common phenomenon.The bagged‘Golden delicious’,‘Orin’ and ‘Granny Smith’ had no brown symptom in the peels,while the peels of ‘Fuji’,‘Pink Lady’ and ‘Ruixue’ showed brown symptom.2.The browning of bagging ‘Ruixue’ fruits occurred in the later stage of fruit development.The browning rate and browning index of the fruits treated with special bags were lower than those treated with G bags.The browning rate and browning index of fruits treated with G fruit bag respectively reached 85.56% and 61.11,while the browning rate and browning index of the fruits treated with special fruit bags respectively reached 70%,29.17,200 days after flowering.3.It was found that the lower effective accumulated temperature and the accumulation of day-night temperature difference in the fruit bag may be the key environmental factors that caused the peel browning of the ‘Ruixue’ apples.The correlation coefficients of △STD,△GDD and △PB were higher than the correlation coefficients of other environmental factors and △PB.In the special fruit bag,the correlation coefficients of △STD,△GDD and △PB were 0.88 and 0.881 respectively.In the G fruit bag,the correlation coefficients of △STD,△GDD and △PB were 0.943 and 0.947 respectively.△STD,△GDD and △PB had a curve function relationship of logistic.4.Bagging reduced the content of antioxidants and the activity of antioxidant enzymes,which weakened the antioxidant capacity of the peel of ‘Ruixue’ fruits.The content of flavonoids,carotenoids,anthocyanins,chlorophyll,SOD and POD enzyme activities of bagged ‘Ruixue’ fruits decreased significantly.At the later stage of the development of the ‘Ruixue’ fruits,the content of malondialdehyde of bagged fruits increased sharply,while the CAT enzyme with responding adversity showed a trend of first rising and then falling,and the expression of MdCAT gene also showed a similar trend.The degree of decreasing in polyphenol content of bagged fruits was higher than that of non-bagged fruits.In addition,the PPO enzyme activity and MdPPO1 gene relative expression of bagged fruits were higher than those of non-bagged fruits.5.Observed by optical microscope and scanning electron microscopy,the waxy structure of the non-bagging ‘Ruixue’ fruits was complete,while the waxy structure of the bagging ‘Ruixue’ fruit appeared microcracks.The thickness of the stratum corneum of non-bagging ‘Ruixue’ fruits was significantly higher than that of the bagging fruit.Furthermore,the non-bagging and the non-browning bagged ‘Ruixue’ fruits had complete cell structure,While at the browning parts,the cell structure was damaged and the cell membrane was collapsed.6.Debagging before harvest could alleviate the peel browning of the ‘Ruixue’,and debagging 30 days before harvest(150 days after flowering)had the best effect.In the special fruit bag,the browning rate and browning index were respectively reduced by 29.12% and 12.13,.while in the G fruit bag,the browning rate and browning index were respectively reduced by 50.66% and 22.75.Debagging could increase the content of anthocyanins in the peel.At the same time,debagging could improve the activity of CAT,POD,SOD enzymes and the genes relative expression of MdSOD,MdPOD,MdCAT.Moreover,debagging fruits maintained high phenolic content,low PPO activity and MdPPO1 gene relative expression.