The induction of pre-harvest acetylsalicylic acid treatment on postharvest resistance of Hami melon fruit

WANG Bin; BAI Xiaodong; ZHANG Jingrong; WANG Yi; JIANG Hong; BI Yang

doi:10.13925/j.cnki.gsxb.20170284

Abstract：[Objective] Hami melon (Cucumis melo L.) is a typical local fruit in the Northwest of China,however,postharvest rot of this fruit is a serious concern.Many fungi are involved in the decay of Hami melons,among them,pink rot caused by Trichothecium roseum is an important postharvest disease in the Northwest of China.The disease not only breaks down the quality of the fruit and causes serious postharvest losses,but it also accumulates mycotoxins in the fruit.Although pink rot can be effectively controlled by the application of chemical fungicides,the use of chemical fungicides will lead to pesticide residues in the fruits and also cause pathogen produce resistance and environmental pollution.Therefore,a safer and more effective strategy needs to be developed.In this study,an experiment is conducted to assay the effects of acetylsalicylic acid (ASA) sprayed during fruit development as an induced resistance in the harvested fruit and to also study if phenylpropane metabolism and antioxidant enzymes contribute to induced resistance in the fruit at harvest and during storage.[Methods] The muskmelon,cultivar'Xizhoumi No.17',was used as the material.The plants were sprayed with ASA at 1.0 mmol· L-1 four times during the young fruit period (14 d after flowering),enlarging period (21 d after flowering),netting period (28 d after flowering) and mature period (preharvesting 48 h).We selected commercially mature and uniform sized fruit,without diseases and pests,for our experimental materials.The first step was to remove dust and foreign bodies from the fruit surface using a tap water rinse and then to soak in 2％ sodium hypochlorite solution for 2 mins for surface disinfection,then rinse and dry pack at ambient temperature (25±2 ℃;RH 55％-60％) for storage.T.roseum was isolated from the onset of the typical fruit,using a separation and purification of Potato Dextrose Agra (PDA),in 4 ℃ as part of the conditions for preservation.The effects of treatment on the lesion diameter of the inoculated melon fruit and natural incidence of melon fruit during ambient storage were evaluated.Meanwhile,the activities of the key enzymes and metabolite contents of the phenylpropane metabolism were determined at harvest and during storage,as well as the activities of peroxidase and polyphenol oxidase.[Results] Preharvest treatment effectively inhibited the development of the lesion diameters of the inoculated fruit with Trichothecium roseum and significantly reduced the natural incidence of the fruit during ambient storage.After 7 days of inoculation,the lesion diameters of the treatment fruit were 40.7％ lower than the control.The natural incidence of the treated melons was only half of the control after 28 days of storage.Moreover,the activity of cinnamic acid-4-hydroxylase and the content of flavonoid and lignin were significantly increased by treatment at harvest.Compared with the control,the ASA treatments enhanced 34.4％ of the cinnamic acid-4-hydroxylase activities and increased by 30％ and 7.05％ the contents of flavonoid and lignin at harvest.The activities of phenylalanine ammonia lyase,cinnamic acid-4-hydroxylase and 4-coumaryl coenzyme A ligase and the contents of total phenolics,flavonoids and lignin were significantly higher than the control during storage.The activities of the phenylalanine ammonia lyase,cinnamic acid-4-hydroxylase and 4-coumaryl coenzyme A ligase were 34.4％,84.5％ and 56.3％ higher than the control after 21,14 and 7 days of storage,respectively.After 21 days of storage,the contents of the total phenolics,flavonoids and lignin were 10.3％,17.6％ and 10.1％ higher than the control.Moreover the treatment also notably induced the peroxidase activity at harvest and enhanced the activity of peroxidase and polyphenol oxidase during storage.Compared with the control,the treatment activity of peroxidase was greater than 64％.During storage,the activities of peroxidase and polyphenol oxidase were 0.35 and 2.3 folds higher than the control after 7 and 28 days of storage.[Conclusion] The postharvest disease resistance of Hami melon could be effectively induced by ASA sprayed during fruit development,the partial mechanism is closely related to the activation of phenylpropanoid metabolism and the increase of the activities of peroxidase and polyphenol oxidase.Therefore,preharvest ASA sprayed four times during fruit development is an effective measure to enhance the disease resistance of Hami melon during ambient temperature storage.