| Peach is a famous native fruit in China,but it is very vulnerable to pathogenic infection during picking,transportation and storage,resulting in a large number of decay of peach fruits.The results showed that antagonistic yeast can effectively control the postharvest diseases of fruits and vegetables,and did not cause adverse effects on human body.This project mainly screened a strain of antagonistic yeast which can effectively inhibit peach brown rot,explored its main biocontrol mechanism,and applied its active freeze-dried powder to the preservation of peach.The main research contents are as follows:(1)In this experiment,87 strains of yeast were isolated from the organic orchard in Zhenjiang.An antagonistic yeast Y17 was obtained through in vitro screening and in vivo screening,which could effectively inhibit the brown rot of peach caused by Monilinia fructicola.Through the tests of morphological,physiological and molecular characteristics,it was identified as C.intermedia.In addition,the strain of Y17 was identified as a non-toxic yeast through the acute oral toxicity test in mice.(2)Through in vivo experiments,the optimum concentration of C.intermedia Y17 to inhibit M.fructicola was 1×10~8 cells/mL.After co-culture in PDB,it was found that C.intermedia Y17 could effectively inhibit the germination of M.fructicola spores.Optical microscopy showed that C.intermedia Y17 could be attached to the pathogenic fungal hyphae and inhibit mycelium growth.In vivo experiments,C.intermedia Y17 could induce the the activities of PPO,APX,CAT,PAL,GLU and CHI.Through the back-off experiment,it was found that C.intermedia Y17 could produce volatile substances to inhibit the growth of M.fructicola,and the substances were determined by GC-MS.Its main components are2-Methyl-1-butanol,1-Hexanol,Ethyl caprylate,Isovaleric acid and Phenylethyl Alcohol.(3)The response of M.fructicola to C.intermedia Y17 volatile substances was analyzed by transcriptome.The results showed that the volatile substances produced by C.intermedia Y17 could significantly affect the metabolic and cellular processes of M.fructicola.Three genes related to biomembrane synthesis(Cytochrome P450monooxygenase,Phosphatidylserinedecarboxylase)andimmuneregulation(Glutathione S-transferase)of M.fructicola were down-regulated by RT-qPCR.Three genes related to energy metabolism(ATP synthase,Hexokinase,Acetyl CoA hydrolase)of M.fructicola,the first two are down-regulated,the last one was up-regulated.One gene related to the cell structure(β-1,3-glucanase)of M.fructicola was up-regulated.(4)Optimizing the centrifugal conditions of C.intermedia Y17,the best centrifugal parameters were 6000 r/min,15 min.Preliminary screening of C.intermedia Y17 protective agent by single factor test showed that trehalose,sodium glutamate,sorbitol had the best protective performance.Through the combination design of response surface center,the optimum cryoprotectant formulation was found to consist of 5.43 g/100mL sorbitol+12.45 g/100mL trehalose+13.56 g/100mL sodium glutamate,and the survival rate of yeast could reach 84.21%±0.87%.Finally,the biocontrol and storage efficacy of C.intermedia Y17 active freeze-dry powder were evaluated.The results showed that active freeze-dry powder still had high biocontrol effect,and-20℃is more suitable for the storage of active freeze-dry powder.(5)The active freeze-dry powder was prepared into suspension and applied to peach by soaking method to study the effect of the agent on the storage and preservation of peaches.The results showed that C.intermedia Y17 active freeze-dry powder could effectively control the occurrence of rotting diseases and reduce the loss of water in peach during storage,and maintain the firmness,vitamin C content,soluble solids content,titratable acid content,total phenol content,flavonoid content and the integrity of cell membrane of peach.It has a positive effect on the preservation of peaches after harvest,and has significant economic and social meaning. |
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