Pre-harvest Spraying Salicylic Acid For Increasing Disease Resistance Of Harvested Longan (Dimocarpus Longan Lour.cv.'Fuyan') Fruits And Its Action Mechanism

Longan(Dimocarpus longan Lour.)is a famous specialty of subtropical fruits in China.The fruit commonly is nutrient-rich and known as 'guiyuan'.Longan fruit mature during August to September white the temperature is high,will easily suffer from water loss,pericarp browning and decay after harvest.The fruits will deteriorate at room temperature(28?)after one week storage.'Fuyan'longan(Dimocarpus longan Lour.cv.'Fuyan'),the chief longan cultivar in Fujian Province of China 5 were treated with salicylic acid before harvest,and stored at(28 ± 1)? in this study · The main findings are following:1.Pre-harvest spraying SA treament at 0.5 g · L-1 could lower respiration rate of harvested longan fruits,and delay the increase of cell membrane permeability in pericarp of harvested longan fruits,keep higher contents of TSS,soluble sugar,sucrose,Vc in aril of longan fruits.Moreover kept higher chlorophyll content and lowered carotenoid content in pericarp of longan fruits,inhibited the decreasing of h° value and L value of fruit inside pericarp,inhibited the increasing of contents of TA,reducing sugar in aril of longan fruits,delayed pericarp browning,inhibited aril breakdown,decreased weight loss rate of longan fruits,reduced the decay of longan fruits,kept higher healthy fruit rate.2.Pre-harvest spraying SA treament at 0.5 g · L-1 could enhance the contents of AsA,GSH on and the activities of SOD,APX,GR,inhibite activity of CAT,enhance the H2O2 content,decrease productive rate of O2-,reduced MDA content in pericarp of longan fruits on the day of harvest.During the days of postharvest storage,pre-harvest SA treatment could keep higher contents of AsA,GSH and higher activities of SOD,APX,GR,increased active-oxygen-scavenging capacity of longan fruits' pericarp,and keep lower productive rate of O2-· and MDA content,reduced accumulation of H2O2,reduced the occurrence of disease in longan fruit.3 Pre-harvest spraying SA treament at 0.5 g · L-1 inhibited activities of LOX,lipase,PLD in pericarp of longan fruits during the days of postharvest storage.Therefore,we speculate that pre-harvest spraying SA treament inhibited activities of membrane lipid-degrading enzymes during the days of postharvest,reduced oxidation and degradation of membrane lipid,thus maintained the integrity of cell membrane.4.Pre-harvest spraying SA treament at 0.5 g · L-1 increased activity of CAT and lignin content in pericarp of longan fruits on the day of harvest.Pre-harvest SA treatment increased activities of PAL,GLU,CHI and lignin content in pericarp of longan fruits during the days of postharvest storage.Pre-harvest SA treatment inhibited activities of PPO,POD,and than kept higher total phenolic content in pericarp of longan fruits,thus delayed pericarp browning of longan fruits.From the results,it could be concluded that pre-harvest SA treatment improve the disease resistance of longan fruits,reduced postharvest disease of longan fruits during the days of storage.