| Alternaria is the main pathogenic microorganism causing fruit and vegetable diseases,which can infect fruits and cause rot,resulting in serious economic losses.The prevention and control of Alternaria mainly adopts chemical control,but it has pesticide residues,which will endanger human health.Biological control has the advantages of non-toxic,harmless and pollution-free,and can be used as a relatively safe and effective sterilization method.Lactic acid bacteria(LAB)have been proved to have antifungal activity and biological preservation potential.In order to make good use of the antifungal properties of LAB,it is of great practical value to apply it to biological preservation.Therefore,this paper studies the antibacterial activity and application of antifungal lactic acid bacteria against Alternaria,in order to provide theoretical reference for the development of green,safe and healthy preservation methods.The results of this study are as follows :(1)In order to use lactic acid bacteria to control pear black spot caused by Alternaria gaisen Ap1.A strain with inhibitory effect on A.gaisen Ap1 was screened from three lactic acid bacteria preserved in the laboratory by double-layer plate streaking method and 96-well plate method,and the biological characteristics of antibacterial active substances were preliminarily explored and analyzed.The results showed that Lactobacillus paracasei 37 and Lactobacillus pentosus 86 had obvious inhibitory effect on A.gaisen Ap1,and the cell-free supernatant(CFS)of the two strains had heat resistance.It was preliminarily inferred that the antibacterial active substances in L.pa-37 CFS may be proteins,while the antibacterial active substances in L.pe-86 CFS were mainly acidic substances.(2)In order to further explore the antibacterial activity of lactic acid bacteria against Alternaria,the antibacterial ability of lactic acid bacteria against Alternaria was analyzed from the morphological point of view.The effects of cell-free supernatant concentrate(CFSC)of the two strains on the hyphae and spores of A.alternata were determined by agar column method and microdilution method.The morphological changes of A.alternata before and after treatment were investigated by electron microscopy,fluorescence staining and microplate reader,and the antibacterial mechanism of antibacterial active substances was preliminarily determined.The results showed that the antibacterial effect of L.pa-37 CFSC was better than that of L.pe-86 CFSC,and the minimum inhibitory concentration of the two strains CFSC against Alternaria was 32 mg / m L.L.pe-86 CFSC had more significant differences in inhibiting spore germination and biomass(P < 0.05).After CFSC treatment,the cell membrane,cytoplasm and organelles of Alternaria were damaged,and the permeability of plasma membrane was increased.Thereby disrupting the internal environment of Alternaria cells,causing Alternaria spores to lose germination ability,abnormal mycelial growth,and even fracture,resulting in a large number of cell content logistics,eventually leading to pathogen death.(3)In order to enrich the application of lactic acid bacteria in biological preservation,the effect of cell-free supernatant treatment of lactic acid bacteria on the storage quality of Korla fragrant pear was studied.The results showed that the preservation effect of L.pe-86 CFSC was more significant than that of L.pa-37CFSC(P<0.05)under room temperature storage conditions.L.pe-86 CFSC treatment could more effectively reduce the decay rate and weight loss rate,and effectively maintain the hardness,chlorophyll and soluble solids content of fragrant pears,indicating that L.pe-86 CFSC treatment could solve the problems of rapid deterioration and easy decay of fragrant pears after harvest to a certain extent.In summary,the antibacterial effect of L.pe-86 CFSC is more significant than that of L.pa-37 CFSC,and it has more potential to replace traditional fungicides to control postharvest quality deterioration of Korla fragrant pear. |
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