Effects Of Exogenous Melatonin On Superficial Scald Of‘White Winter Pearmain’ Apple

Superficial scald is a common physiological disease of apples in low-temperature storage,which decreases the commodity value of apples seriously.Currently,the using of chemical treatments such as 1-methylcyclopropene（1-MCP）and diphenylamine（DPA）is still an effective method for preventing the superficial scald.So it is necessary to find more natural and effective treatments to prevent the occurrence of superficial scald because of the increasing safety problems of chemical treatments.Melatonin is a natural indoleamine hormone,which has enormous biological functions such as growth regulation and oxidation resistance.In this study,‘White Winter Pearmain’apples were treated with melatonin concentrations of 0,0.2m M,1m M and 5m M,and compared with DPA treatment.The effects of melatonin on the occurrence of superficial scald and fruit quality were investigated.The results showed that:（1）0.2m M,1m M and 5m M melatonin delayed the decreases of fruit firmness significantly,and 1m M melatonin treatment was higher than that of 0.2m M and 5m M treatment.The soluble solid content treated with melatonin and DPA was significantly lower than that of the control,which effectively maintained the quality of fruits and prolonged the storage life.（2）The effects on superficial scald were varied from different concentrations of melatonin:1m M and 5m M melatonin reduced the incidence and index of superficial scald,and 1m M treatment was more effective in preventing the scald.In contrast,0.2m M melatonin promoted the occurrence of superficial scald.DPA had the lowest incidence.（3）Gene expression analysis showed that the expression ofα-Farnenase synthase gene Md AFS and ethylene biosynthetic genes Md ACO1 and Md ACS1 were down-regulated under1m M and 5m M treatments.Both 1m M and 5m M melatonin decreased the contents ofα-Farnesene and CTols,the ethylene release peaks were delayed in apples,while 0.2m M melatonin increased the ethylene production,α-Farnesene and CTols contents in middle and late storage.Among all treatments,DPA inhibited ethylene,α-Farnesene and CTols most significantly.（4）0.2m M,1m M,5m M melatonin and DPA treatments increased the activities of superoxide dismutase（SOD）,peroxidase（POD）,catalase（CAT）and ascorbate peroxidase（APX）in the enzymatic antioxidant system;DPA,1m M and 5m M melatonin treatment obviously delayed the decreases of total phenol content and DPPH·scavenging rate,and promoted the increase of total flavonoid and endogenous melatonin content in fruits.（5）0.2m M,1m M,5m M melatonin and DPA treatments decreased the relative electrical conductivity,malondialdehyde（MDA）,superoxide anion（O₂^-·）and hydrogen peroxide（H₂O₂）in low-temperature storage,which played a role in scavenging reactive oxygen species and maintaining the structural stability of cell membranes.