Study On The Fresh-keeping Of Longan (Dimocarpus Longan Lour.)Fruit And The Control And Mechanism Of The Postharvest Diseases By Biocontrol Bacteria Bacillus Amyloliquefaciens LY1

Longan(Dimocarpus longan Lour.)is one of the main subtropical fruits in China.Since longan fruit matures during the hot season,it is easy to brown,deteriorate and even decay after harvest,which show a serious effect on its edible value and commodity value.Our previous' studies showed the quality deterioration of fruit was caused by the infection from pathogenic fungi,and Lasiodiplodia theobromae(Pat.)Griff.&Maubl.is one of the main pathogens which reduces longan fruit's qualitiy during its storage.Bacillus amyloliquefaciens LY1 was isolated and identified in our laboratory,Our previous'preliminary studied found that Bacillus amyloliquefaciens LY1 had better fresh-keeping effect of longan fruit after harvested and could effectively inhibit the infection of Lasiodiplodia theobromae(Pat.)Griff.&Maubl.But the mechanism of effect is still unknown.Basing on longan(Dimocarpus longan Lour.cv.'Fuyan'),the fresh-keeping effect of longan fruit after harvested by biocontrol bacteria Bacillus amyloliquefaciens LY1 treatment,and the inhibition and its action mechanism of Lasiodiplodia theobromae(Pat.)Griff.&Maubl.were studied in this paper.The results are as follows:(1)After the treatment of fermentation liquid for Bacillus amyloliquefaciens LY1,the longan fruit's decay rate was 36%,weight loss rate was 2.40%,browning degree was 0.43 and disease index was only 0.62 after its storage for 6 days under the condition of 28?;The physiological metabolism of longan fruit inoculated Lasiodiplodia theobromae(Pat.)Griff.&Maubl kept normal after the treatment of Bacillus amyloliquefaciens LY1,and had enhanced the storability of longan fruit that kept the fruit respiration,weight loss rate and browning degree change to flatten.The control one had already rotten in the sixth day of storage and Lasiodiplodia theobromae(Pat.)Griff.&Maubl.had already rotten in the fifth day,which showed the fermentation liquid of Bacillus amyloliquefaciens LY1 had fresh-keeping effect.(2)The antioxidant enzymes(SOD,CAT,APX)activities and antioxidant substances(AsA,GSH,flavonoids)content of the pericarp were increased by the treatment of Bacillus amyloliquefaciens LY1,then the ability of the peel to scavenge active oxygen was enhanced and the production rate of O2-· was decreased.The treatment of Lasiodiplodia theobromae(Pat.)Griff.&Maubl.enhanced the ability to scavenge active oxygen but couldn't clear the massive accumulation of O2-·,which promoted the lipid peroxidation and rised the MDA and LOX.As Bacillus amyloliquefaciens LY1 weaked the poisonous effect on peel from bacteria,the co-treatment delayed the membrane lipid peroxidation and inhibitioned the increasing of LOX activity and MDA content,but made a higher membrane lipid peroxidation of the peel than the treatment of Bacillus amyloliquefaciens LY1 individualiy.(3)Bacillus amyloliquefaciens LY1 could induce the longan fruit to produce the reaction of stress and enhance the activitie of PPO,that promoted the synthese of phenolic substances and made the peel enhence the ability to resistant pathogenic invading.The reaction of stress was the same as its production by pathogenic invading.As Bacillus amyloliquefaciens LY1 could inhibit the growth of the pathogenic,the degree of the structure of cells compartmentalization of the longan fruit was lower,that showed the lower degree of browning on the appearance of the peel.The treatment of Lasiodiplodia theobromae(Pat.)Griff.&Maubl.consumed a lot of phenolic substances of the longan peel and severely damaged the cell structure,as the increasing of PPO activity,the enzymatic browning exacerbatied and the brown of peel increased.The degree of browning of the co-treatment was closed to the control due to that the Bacillus amyloliquefaciens LY1 inhibitioned the consumption of phenolic substances casued and destruction of cell structure by bacteria,and the gentle changed of PPO activity,the cell structure integrity was closed to the control too.(4)In the aspects of disease resistance,Bacillus amyloliquefaciens LY1 inoculationed for one day all induced the peel to increase the activities of POD,PAL,CHI and GLU,which was the self-defense reaction of the fruit at an aim to accelerate biosynthesis of lignin that can enhance enhanced cell wall's mechanical strength and trengthen the attack of peel to germs,then enhanced the resistance to disease and reduced the disease situation.The treatment of Lasiodiplodia theobromae(Pat.)Griff.&Maubl.increased the activities of disease resistance enzymes and synthesized a large number of Lignin.As the activity of PAL rapidly declined,causing the physiological metabolic of Lignin imbalanced and the lignin degradated to hazardous substances on bacteria,while the activities of CHI and GLU rapidly declined,weakened the attack of peel to germs;except for the first day after inoculating Bacillus amyloliquefaciens LY1,the increased of POD,PAL,CHI and GLU activities became slower later,which showed that Bacillus amyloliquefaciens LY1 could have a long effect on the pathogen and inhibited the process of corruption of the longan fruit.