Effects On The Control Of Black Spot Disease And The Expression Of WRKY Gene In Postharvest Muskmelon Fruits By Nitric Oxide Fumigation Treatment

Muskmelon(Cucumis melo L.)fruit is a famous fruit representing an especial variety of Xinjiang.However,the muskmelon fruits becomes perishable easily because of the temperature is high in harvest season.Muskmelon fruits turns decay mainly due to the reason that the black spot caused by Colletotrichum Alternaria(Alternaria alternata).Fungicide is very effective to control the disease;owing to the safety problem is limited.Therefore,it is an urgent problem to find an effective method to control the postharvest diseases in the muskmelon storage and transportation industry.Xinjiang muskmelon fruits(cv.Xizhoumi)were taken as the test materials in this paper.60 ?L/L nitric oxide(NO)gas was used for fumigation of muskmelon fruit and inoculated with A.alternata,the effects of NO treatment on storage quality,reactive oxygen species metabolism,phenylpropanoid metabolism,cell wall metabolism and the changes of pericarp ultrastructure in muskmelon fruits were researched.The gene expression of postharvest muskmelon by transcriptome sequencing with NO treatment was studied.WRKY gene involved in the expression and the regulation of metabolic pathway were analyzed.The effects on the control of black spot disease and the expression of WRKY gene in postharvest muskmelon fruits by NO treatment was investigated,which provided some theoretical reference for the control of postharvest disease resistance induced by NO treatment.The main results are as follows:(1)The natural incidence,disease index,respiration rate and ethylene production were lower than those in control group,the soluble solids content and titratable acid content were efficiently kept,the hardness and ascorbic acid content were inhibited in muskmelon fruits by the treatment of 60 ?L/L NO.It is suggested that the storage quality of postharvest muskmelon fruits is better maintained by the treatment of NO.(2)The effect on the metabolism of reactive oxygen by NO treatment during the postharvest storage in muskmelon fruits was investigated.The results showed that the lesion diameter and lesion depth were significantly inhibited,the accumulation of reactive oxygen species was induced rapidly in early storage,the SOD,POD and CAT activity of antioxidant enzymes was increased in the storage.It is indicated that the improvement of disease resistance is closely related to the regulation of reactive oxygen species metabolism induced by NO treatment.(3)The changes of postharvest disease resistance and defense substance were studied.The results indicated that the activity of PAL,C4 H,4-CL,CHT,?-1,3glucanase were increased,the accumulation of total phenolic compounds and lignin content was promoted.However,the promoting effect of flavonoid content was not significant.It is suggested that the results indicated that the increase of disease resistance was induced with exogenous NO treatment by enhancing the phenylpropanoid metabolism pathway and improving the activity of disease related proteins,which could inhibit the occurrence of fruit diseases.(4)The effects of NO treatment on cell wall metabolism of muskmelon fruits were further discussed.The result showed that the activity of PG,PME and Cx were inhibited,the content of protopectin and cellulose were increased,and the cell membrane permeability,soluble pectin content were decreased by NO treatment.The growth of mycelium on the surface and in the crack of pericarp were inhibited,the integrityof stomatal structure was maintained better by NO treatment.It is suggest that the damage of pathogens to the epidermal structure of fruit was reduced and the disease resistance were enhanced through the regulation of cell wall metabolism induced by NO treatment.(5)The transcriptome of muskmelon pulp at 0 d,6 d and 10 d was sequenced by high-throughput sequencing technique.The result showed that the expression of genes related to carbon metabolism,plant hormone signal transduction pathway,phenylalanine metabolism and phenylpropanoid(phenolic,flavonoid and lignin)biosynthesis were induced by NO treatment.WRKY gene could inhibit the expansion of fruit lesions and participate in the regulation of MAPK cascade,cell wall reinforcement,cell hypersensitive response and expression of resistance related genes in plant-fungal interactions.These results indicated that WRKY gene is involved in the regulation of fruit disease resistance,the expression of disease resistance related genes and start the fruit's own defense reaction system to inhibit the disease induce by NO treatment.