Study On The Biocontrol Efficacy Of Pichia Caribbica Against Postharvest Diseases Of Cherry Tomato And The Involved Mechanisms

Cherry tomatoes are susceptible to pathogenic infection in the process of storage,transportation and sale,which results decay and huge economic losses.Alternaria alternata is one of the main pathogens of cherry tomatoes.Fruits infected by this pathogen produce gray brown or black spots and gradually become soft and rotten.At present,the control of postharvest diseases of cherry tomatoes mainly uses chemical fungicides.But long-term use of chemical fungicides is easy to cause drug resistance of pathogens,pollution to the environment,and harm to the health of consumers.Controlling postharvest diseases of fruits and vegetables with antagonistic microorganisms has the advantages of high safety,high efficiency and being friendly to the environment.Therefore,it has a broad application prospect.However,there are few researches on the control of postharvest diseases of cherry tomatoes by antagonistic yeast,especially black spot disease,and the control mechanisms are not clear.In this paper,the antagonistic yeast with good control efficacy against postharvest black spot and natural decay was screened and its physiological mechanism of controlling cherry tomatoes postharvest disease and its molecular mechanism of inducing cherry tomatoes disease resistance were revealed,which provided a theoretical reference for the biological control of cherry tomatoes postharvest disease and had a certain practical application value for the storage and preservation of cherry tomatoes.The main research results are as follows:（1）Pichia caribbica,an antagonistic yeast,which has a good control effect on black spot disease of cherry tomatoes was screened from 5 strains of yeasts preserved in the laboratory through in vivo and in vitro tests.（2）The control efficacy of P.caribbica at different concentrations against postharvest black spot of cherry tomatoes was investigated.P.caribbica at 1×10⁸and 1×10⁹cells/m L showed the better control efficacy.Furthermore,P.caribbica at 1×10⁸cells/m L could significantly reduce the natural decay rate of cherry tomatoes,and had no adverse effect on the storage quality.（3）The physiological mechanisms involved in controlling postharvest diseases of cherry tomatoes by P.caribbica was studied through in vitro and in vivo experiments.P.caribbica mainly controlled the postharvest disease of cherry tomatoes through the following aspects:P.caribbica could directly inhibit the growth of pathogens by inhibiting A.alternata spore germination,bud tube elongation and parasitism on its hyphae.P.caribbica could colonize rapidly on cherry tomatoes,thus occupying living space and competing with pathogens for nutrition and indirectly inhibiting pathogen growth.P.caribbica increased the activities of antioxidant enzymes and enzymes in ascorbate-glutathione（ASA-GSH）and glutathione peroxidase（GPX）cycles assigned to enzymatic scavenging system of reactive oxygen species（ROS）,and the contents of non-enzymatic scavenging system component,thus reducing ROS content of cherry tomatoes.The content of malondialdehyde（MDA）which was a product of membrane lipid peroxidation was then decreased in cherry tomatoes.（4）The molecular mechanisms involved in the induced disease resistance of cherry tomatoes by P.caribbica were analyzed based on transcriptomic technology and bioinformatics.P.caribbica induced the expression of related genes in MAPK and Ca²⁺signaling transduction pathways,the related genes in plant hormone signaling pathways including IAA,ET,ABA,SA and JA signaling transduction pathways,the downstream genes related to defense response,the genes related to ROS scavenging and the genes participating in the synthesis of resistant secondary metabolites,thus enhancing the fruit disease resistance.