Study On Indoor Pesticide Screening And Antagonistic Bacteria Of Sclerotinia Stem Rot Of Allium Victorialis

Allium victorialis is a wild vegetable widely distributed in the north temperate zone.It is rich in nutrition and a variety of physiological active substances.With the popularization of artificial planting and the development of related research,its economic value and research value are paid more and more attention.The disease of Allium victorialis seriously affects the yield and quality,which has been paid more and more attention.A new disease,Sclerotinia stem rot of Allium victorialis,was found in Heilongjiang Forest Botanical Garden.In this study,the pathogenic fungi was isolated from the diseased Allium victorialis,and their pathogenicity was verified.Indoor pesticide screening and antagonistic isolation were carried out to provide theoretical reference for the prevention and control of the disease.A potential pathogenic fungus XJH was isolated from the infected Allium victorialis.Verified by Koch’s law,strain XJH was confirmed to be the pathogen of Sclerotinia stem rot of Allium victorialis.After morphological observation and molecular biological identification,XJH,the pathogen of Sclerotinia stem rot of Allium victorialis was identified as Sclerotinia sp.The optimum growth conditions of strain XJH were studied.The results showed that the optimum growth temperature was 20℃,the optimum p H was 6,the optimum carbon source for mycelial growth was maltose and the optimum nitrogen source was glutamine.Four common low toxicity pesticides,thiophanate methyl,chlorothalonil,carbendazim and Dithane z-78,were selected to carry out antifungal test on Sclerotinia sp.XJH and explore its toxicological characteristics.The results showed that the minimum inhibitory concentration of thiophanate methyl on XJH mycelial growth was 0.4μg·m L^-1,the concentration for 50%of maximal effect is 1.457μg·m L^-1;The minimum inhibitory concentration of chlorothalonil on XJH mycelial growth was 4μg·m L^-1,the concentration for 50%of maximal effect is 0.9404μg·m L^-1;the minimum inhibitory concentration of carbendazim on mycelial growth was 14μg·m L^-1,the concentration for 50%of maximal effect is 9.146μg·m L^-1;the minimum inhibitory concentration of Dithane z-78 on its mycelial growth was 20μg·m L^-1,the concentration for 50%of maximal effect is 229.1μg·m L^-1.The rhizobacteria Bacillus velezensis 1AXXS,Bacillus siamesis 1AXR,and the root endophytic bacteria Bacillus subtilis 2AX2R and Bacillus mojavensis 32X1R,which have potential inhibitory effect on Sclerotinia sp.XJH,were isolated from healthy Allium victorialis.The four bacteria have antagonistic activity against XJH,and the inhibition rate can reach46.54%.The extracellular volatile products of strains 1AXXS and 32X1R have certain antifungal properties and can inhibit the mycelial growth of XJH.The lipopeptide produced by strain 1AXXS mainly contains surfactin,and its minimum inhibitory concentration on XJH mycelial growth is 3μg·m L^-1,and its concentration for 50%of maximal effect is 9.473μg·m L^-1.1AXXS lipopeptide can seriously damage the permeability of XJH mycelial cell membrane,resulting in cytoplasmic dissolution.After treatment with lipopeptide,the conductivity of XJH extracellular fluid increased by 85%,nucleic acid leakage increased by 51%,protein leakage increased by 71%,and soluble sugar loss increased by13.32%.Lipopeptide treatment could induce the production of reactive oxygen species in XJH mycelial cells,resulting in oxidative stress.The content of intracellular malondialdehyde increased by 120%,the activity of superoxide dismutase decreased by 28.34%,and the activity of catalase decreased by 70.97%.