Studies On Bacillus Amyloliquefaciens MG-3 For Controlling The Disease Development Of Harvested Litchi Fruit Caused By Peronophythora Litchii And Its Mechanism

Litchi(Litchi chinensis Sonn.)is a famous tropical and subtropical fruit with high nutritional and commercial value.However,the high temperature and humidity at its harvested season easily causes the latent pathogen to infect the fruits with a result of pericarp browning and fruit deterioration.These greatly limited the sales of litchi fruits.Some research discovered that the Peronophythora litchii(P.litchii)is the primary latent pathogen which caused the litchi pericapr browning and deterioration.Bacillus amyloliquefaciens MG-3 is a type of biocontrol bacteria.It has a strong ability to generated secondary metabolite and inhibited the fungual growth and reproduction.In this paper,we were used 'Wuye' litchi(Litchi chinensis Sonn.),the major litchi cultivar in Fujian Province of China,as the experiment material,and used the Bacillus amyloliquefaciens MG-3,which contain 1×108 CFU/mL live bacteria and and incubation time 56 h,to treat the P.litchii-inoculated litchi fruit.this study focus on the effects of Bacillus amyloliquefaciens MG-3 controlling litchi disease caused by P.litchii and their relationship between different physiology,quality,storage,reactive oxygen,cell membrane,metabolisms of energy,antifungal substance.The aim of this study was to investigate the mechanism of Bacillus amyloliquefaciens MG-3 controlling the disease development of harvest litchi fruit infected by P.litchii.so as to provide the scientific theory and alternative methods for disease control.The main results were as follows:1.Bacillus amyloliquefaciens MG-3 controlled disease caused by P.litchiiinoculated litchi fruit and relationship between physiology,quality,storage.it could delay the increase of cell membrane permeability and respiration rate of litchi fruit.kept higher contents of total soluble solids(TSS),titratable acid(TA),total sugar,sucrose,reducing sugar and vitamin C(Vc)in pulp of litchi fruit,It also kept higher contents of chlorophyll,carotenoid,anthocyanin,flavonoidand,total phenolics in pericarp of litchi fruit,delay pericarp browning and diseasing,reduced the decay of litchi fruits and decreased lose weight percent,kept lower fruit rotting percentage.2.Bacillus amyloliquefaciens MG-3 controlled disease caused by P.litchiiinoculated litchi fruit and relationship between reactive oxygen metabolism.It could effectively decreased the O2-· production rate of P.litchii-inoculated litchi fruit,reduced the products malondialdehyde(MDA)of membrane peroxide reaction,kept higher the activities of reactive oxygen scavenging enzymes(superoxide dismutase(SOD),catalase(CAT)and ascorbate peroxidase(APX)),reduced the contents of reactive oxygen scavenging substance(ascorbic acid(AsA)and reduced glutathione(GSH)),and then inhibited the reduce of the 1,1-diphenyl-2-picrylhydrazyl(DPPH)scavenging ability and reduction ability,and maintained the balance between ROS production and scavenging,alleviated the membrane peroxide.3.Bacillus amyloliquefaciens MG-3 controlled disease caused by P.litchiiinoculated litchi fruit and relationship between membrane lipid metabolism.It could significantly decreased the activities of phospholipase D(PLD),lipase and lipoxygenase(LOX)(enzymes related to fatty acid degradation)in the pericarp of P.litchii-inoculated litchi fruit,kept lower the relative content of capric acid(C10:0),palmitic aicd(C16:0)and stearic acid(C18:0),inhibited the reduce of the degradation of oleic acid(C18:1),linoleic acid(C18:2)and linolenic acid(C18:3),alleviated the degradation of unfatty acid and the increase of fatty acid,maintained higher unsaturated fatty acid(U/S)and index of unfatty acid(IUFA),finally protected the membrane integrity.4.Bacillus amyloliquefaciens MG-3 controlled disease caused by P.litchiiinoculated litchi fruit and relationship between energy metabolism.It could maintained the higher level of ATP,ADP and energy charge,lower level of AMP,increased the activities of Ca2+-ATPase,H+-ATPase and Mg2+-ATPase in protoplasm,vacuole and mitochondria,maintained ion balance.During the later storage,It could significantly inhibited the activities of CCO,PPO and matained low the activities of AAO in the pericarp of litchi fruit,increased the activities of NAD kinase decreased the content of NAD and NADH,and increased the NADP and NADPH content,protected the membrane structure.5.Bacillus amyloliquefaciens MG-3 controlled disease caused by P.litchiiinoculated litchi fruit and relationship between disease resistance metabolism.During the later storage,It significantly maintained higher the content of lignin,the activities of PAL,POD,CHI and GLU.It lead to enhance the disease resistance.