Study On The Biocontrol Efficacy Of Meyerozyma Guilliermondii On Postharvest Desiease Of Broccoli And The Involved Mechanisms

Black spot caused by Alternaria brassicicola is one of the most common fungal disease with the highest incidence during the period of storage,transportation and sales of postharvary broccoli.The decay and quality deterioration caused by this disease can result in huge economic losses.Biological control using antagonistic yeast has been widely used in the control of postharvest diseases of fruit and vegetables and has achieved good effects due to the high efficiency and safety.However,there are few reports on the application of antagonistic yeast in the biocontrol of postharvest disease of broccoli,and the involved mechanisms are not clear.In this study,antagonistic yeast which could control black spot and natural rot of postharvary broccoli is to screen from healthy broccoli.By studying the effects of this antagonistic yeast on reactive oxygen species(ROS)metabolism,respiration metabolism and energy state of broccoli,and analyzing the effects of this antagonistic yeast on the metabolites of broccoli based on metabolomics technology and bioinformatics,the mechanisms of controlling postharvest diseases of broccoli by this antagonistic yeast was preliminarily revealed.It provides theoretical and technical support for the application of antagonistic yeast in the control of postharvest diseases of broccoli,and has practical application value for preserving postharvest broccoli.The main findings are as follows:(1)A.brassicicola was isolated from infected broccoli.It was confirmed to be the pathogen of black spot of postharvary broccoli based on Koch's rule.(2)Meyerozyma guilliermondii was screened from healthy broccoli and confirmed to be non-toxic by acute oral toxicity test.(3)The control effect of M.guilliermondii with different concentrations on postharvest black spot of broccoli was investigated.The results showed that 1×10⁸cells/m L of M.guilliermondii had the significant control effect on postharvest black spot of broccoli,and could significantly reduce the disease index of natural decay of broccoli.Moreover,this antagonistic yeast could alleviate the deterioration of broccoli.(4)The mechanisms of the control of postharvest diseases of broccoli by M.guilliermondii was studied by investigating the effects of M.guilliermondii on the activities of enzymes related to respiratory metabolism,the activities of ROS metabolism-related enzymes and the contents of related substances,the energy state of postharvest broccoli.The results showed that M.guilliermondii could increase the activities of pyruvate kinase(PK),succinatedehydrogenase(SDH),glucose-6-phosphate dehydrogenase(G6PDH)and cytochrome C oxidase(CCO)in the early stage of storage,but reduce the activities of these enzymes in the late stage,thus provided sufficient material source and energy for life activities,and could reduce the respiration metabolism of broccoli in the later stage and delay its senescence.The yeast treatment could also increase the energy charge(EC)level to maintain the high energy state of broccoli.M.guilliermondii treatment can also enhance the activities of ROS metabolism-related enzymes such as peroxidase(POD),catalase(CAT),ascorbate peroxidase(APX),superoxidedismutase(SOD),glutathione reductase(GR)and glutathione peroxidase(GPX),reduce the contents of H₂O₂ and O₂^-and the content of membrane lipid peroxide malondialdehyde(MDA),so as to improve the antioxidant capacity of broccoli and enhance its disease resistance.(5)The disease resistance of broccoli interacting with M.guilliermondii was improved mainly by affecting the contents of related substances involved in glutathione metabolism,fatty acid metabolism,sugar metabolism and nucleotide metabolism,and enhancing the synthesis of resistant secondary metabolites such as phenols,terpenoids and alkaloids.