Stability and Mechanism of Wheat Straw Fermentation Products of Chaetomium globosum Against Phytophthora capsici
[Objective]Crop blight caused by Phytophthora capsici has caused huge economic losses to crop industries such as pepper.The aim of this paper is to explore the inhibition stability and mechanism against P.capsici by metabolites of Chaetomium globosum,and to provide references for the research and development of microbial fungistatic agents for the inhibition of P.capsici.[Method]To investigate the thermal,acid-base,light and time stability of the crude extract against P.capsic,the crude extracts were treated at different temperatures(40-121℃),pH(1-13),light times(0-12 d)and storage times(0-60 d),and the inhibition rate of crude extracts against P.capsici after different treatments was determined by mycelial growth inhibition method.The effect of the crude extract on the mycelia morphology of P.capsici was observed by optical microscopy.The effects of the crude extract on cell wall,cell membrane,active oxygen metabolism,protein content,reducing sugar content and pathogenicity of P.capsici after being treated with P.capsici for 12-72 h were investigated by various physiological and biochemical experiments.[Result]Within the treatment range set in this experiment,the inhibition rate of the crude extract(1 mg·mL-1)against P.capsici did not decrease significantly after treatment with different light times and storage times,and the inhibition rate remained at about 93%.The inhibition rate of crude extract against P.capsici did not decrease significantly in the heat treatment range of 40-70℃,while the heat treatment above 70℃significantly reduced the inhibition rate,but the inhibition rate was not less than 70%.The inhibition rate of crude extract against P.capsici was significantly reduced in the acid-base treatment range of pH 1-5 and pH 9-13,but the inhibition rate was also not less than 70%.The treatment of crude extract affected the morphology of P.capsici mycelia,caused severe distortion and shrinkage of mycelia,and also affected the metabolism of active oxygen species,resulting in large accumulation of active oxygen species in mycelia.The alkaline phosphatase activity,β-glucosidase activity,nucleic acid and protein contents in culture medium of P.capsici were significantly increased after being treated with crude extract for 12-72 h,and the contents of malondialdehyde and hydrogen peroxide in P.capsici mycelia were significantly increased.Catalase activity and the contents of soluble protein and reducing sugar in the mycelia of P.capsici were significantly decreased within 12 to 72 h after the crude extract treatment,but the activities of superoxide dismutase,peroxidase,polygalacturonase and β-glucosidase were significantly decreased only for a certain time.[Conclusion]In the treatment range set in this experiment,the inhibition effect of the crude extract of C.globosum wheat straw fermentation is not affected by the light and storage time,but the heat treatment of more than 70℃and the pH treatment of 1-5 and 9-13 significantly reduce the inhibition effect of the crude extract against P.capsici.In addition,the crude extract inhibits P.capsici by changing the morphology of mycelia,damaging cell walls and membranes,causing intracellular material leakage,reducing the contents of protein and reducing sugar in mycelia,inhibiting the activity of antioxidant enzymes,interfering the metabolism of reactive oxygen species and causing a large accumulation of reactive oxygen species.
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