Pre-harvest Kadozan Treatment For Increase Disease Resistance Of Harvested Litchi Fruit And Its Action Mechanism

Litchi(Litchi chinensis Sonn.)is a famous subtropical fruit in China.Since litchi fruit mature in the hot and humid summer,the fruit deteriorate quickly after harvest due to rapid pericarp browning and fruit decay,which limit its long-distance transportation,marketing and consumption.'Wuye' litchi(Litchi chinensis Sonn.),the major litchi cultivar in Fujian Province of China,were used as the experiment material The objectives of this research was to investigate the optimum conditions of pre-harvest Kadozan treatment for maintaining fruit quality,improving disease resistance and prolonging storage life of 'Wuye' fruit and clarify the mechanism of Kadozan treatment for improving resistance of harvested 'Wuye' fruit by investigating active oxygen metabolism,membrane lipid metabolism,tissue energy metabolism and disease-resistant material metabolism.The major results were showed as follows:1.Compared with the control fruit,pre-harvest treatment with different concentrations of Kadozan(diluted 250,500,750 and 1000 times respectively)could improve the size,weight and eatable rate of litchi fruit,keep higher contents of total soluble solids(TSS),titratable acid(TA),total soluble sugar,sucrose,reducing sugar and vitamin C(Vc)in litchi aril,delay the increase of cell membrane permeability in pericarp of litchi fruit and lower the respiration rate and derease weight loss of litchi fruit.The Kadozan treatment could also keep higher contents of chlorophyll,carotenoid,anthocyanin,flavonoid and total phenolics in pericarp of litchi fruit,delay pericarp browning,reduced the decay of litchi fruits and keep higher healthy fruit rate.Among the above treatments,the fruits treated with Kadozan diluted by 750 times showed the best disease-resistant.From the results,it could be concluded that pre-harvest treatment with Kadozan diluted by 750 times could be used as the optimum conditions for maintaining fruit quality and prolonging storage life of 'Wuye' litchi fruit during the postharvest storage at(25±1)?.2.Pre-harvest Kadozan treament could enhance the contents of ascorbic acid(AsA),glutathione(GSH),flavonoid and the activities of superoxide dismutase(SOD),catalase(CAT),ascorbate peroxidase(APX),decreased the productive rate of O2-,reduced malondialdehyde(MDA)content in pericarp of lithi fruits on the day of harvest.During the days of postharvest storage,pre-harvest Kadozan treatment could keep higher contents of AsA,GSH,flavonoid and higher activities of SOD,CAT,APX,increased active-oxygen-scavenging capacity of litchi fruit's pericarp,kept lower productive rate of O2-· and MDA content and reduced the accumulation of reactive oxygen species(ROS)which can undermine cell membrane structure.3.Pre-harvest Kadozan treament inhibited activities of phospholipase D(PLD),lipase and lipoxygenase(LOX),maintained higher relative contents of unsaturated fatty acids,such as oleic acid,linoleic acid,linolenic acid,etc.and lower relative contents of saturated fatty acids,such as capric acid,palmitic acid,stearic acid,etc in pericarp of litchi fruit during the days of postharvest storage.As a result,the decrease of the index of unsaturated fatty acids(IUFA)and unsaturated degree of fatty acids were inhibited and the integrity of cell membrane was maintained.4.Pre-harvest Kadozan treament could maintain higher contents of adenosine triphosphate(ATP)and adenosine diphosphate(ADP)and a higher level of energy charge in pericarp of litchi fruit during the days of postharvest storage.What's more,the treatment kept higher activity of ATPase,cytochrome c oxidase(CCO)and NAD+kinase(NADK),inhibited the decrease of NADP(H)contents and maintained lower contents of NAD(H).5.Pre-harvest Kadozan treament increased the contents of total phenolics and lignin in pericarp of litchi fruit on the day of harvest and inhibited their decrease during storage time.The treatment also inhibited the activities of polyphenoloxidase(PPO),peroxidase(POD),and then kept higher total phenolic content in pericarp of litchi fruits.In addition,the activities of disease defense-related enzymes,such as phenylalanine ammonialyase(PAL),chitinase(CHI)and ?-1,3-glucanase(GLU)were maintained at higher levels.From the results,it could be concluded that pre-harvest Kadozan treatment improve the disease resistance of litchi fruit,reduced postharvest disease of litchi fruit during the days of storage.