Study On Effects And Mechanisms Of Meja Treatment On Quality Maintenance In Table Grape

Table grapes are rich in nutrition and they are very popular with consumers for their soft and juicy,sweet and sour.However grapes are likely to exhibit dehydration,wilting,shattering,dry stems,decay incidence and other symptoms in the post-harvest storage and transportation process of aging.These symptoms greatly reduce the quality and value of the goods of grapes.There are about 27%of the grape losses due to postharvest decay in the world.Currently,the most common method to control postharvest diseases of grapes is the use of SO2 gas,either by repeated fumigation in storage rooms,or by packing the grapes in polyethylene-lined boxes with SO2 generators.However,SO2 can damage grapes manifested as bleaching the berries and discolorating the rachis,and induce allergy phenomena in sensitive individuals,which limit the commercial application of SO2 in many countries.Therefore,many alternative approaches are explored to control postharvest decay of grapes.The objectives of this study were to evaluate the MeJA efficacy and the possible mechanisms involved in harvested table grapes.The results were as follows:1.Appropriate concentration of MeJA fumigation treatment can effectively inhibit decay rate,abscission rate and stem quality in harvested table grapes.10 μmol/L MeJA treatment were the most effective in those concentration.However,1000 μmol/L MeJA vapor caused injury.10 μmol/L MeJA vapor treatment inhibited the increase of decay rate,abscission rate,and delayed the decrease of firmness,TA,L*value,total phenols and flavonoids,while MeJA had no significant effect on C values and pH values of the fruit.As a result,10 μmol/L MeJA maintained the quality of grapes,and extend the grapes shelf life.2.10 μmol/L MeJA vapor treatment resulted in significantly lower decay rate.The treatment maintained the high content of total phenols and flavonoids,increased hydroxyl radical scavenging and DPPH radical scavenging activity,and reduced the formation of O2 ·rate.Meanwhile 10 μmol/L MeJA treatment induced activities of PAL、POD、SOD and CAT,inhibit the APX activity,thus resulted in lower level of H2O2 in the late storage.Therefore,10 μmol/L MeJA vapor treatment maintained a high post-harvest grapes antioxidant capacity,maintained a balance of active oxygen metabolism,and delayed the aging speed of postharvest fruit during storage.3.The effect of a postharvest treatment with 10 μmol/L of MeJA on controlling gray mold decay caused by Botrytis cinerea in table grapes and the possible action mechanisms were investigated.The results indicated that MeJA treatment reduced the incidence and development of gray mold decay significantly in grapes.Meanwhile,MeJA treatment markedly enhanced activities of SOD and CAT,decreased the activity of APX,promoted the accumulation of H2O2 and improved the DPPH radical scavenging activity.MeJA treatment also significantly enhanced activities of defense related enzymes including CHI,GNS,PPO,POD and PAL.Moreover,transcripts of the defense related genes in table grape encoding CHI,GNS,SOD,PAL and CAT were only significantly enhanced in fruit pre-treated with MeJA and then inoculated with B.cinerea compared with those that were only treated with MeJA or inoculated with B.cinerea.These results suggested that MeJA treatment primes defense responses for enhanced disease resistance against B.cinerea and thus reducing gray mold decay in harvested table grapes.