The Study Of Biocontrol And Mechanism Of Action On Postharevest Diseases Of Fruits By Cryptococcus Laurentii

Postharvest diseases of fruits cause major losses, these diseases are primarily controlled by application of synthetic fungicides. Alternative methods are needed because of concerns about environmental contamination and human health risks associated with fungicide residues and because the widespread use of these chemicals in commercial packinghouses has led to the proliferation of resistant strains of the pathogens. Microbial biocontrol agents have shown great potential as an alternative to synthetic fungicides for the control of postharvest decay of fruits and vegetables.A strain of yeast that has high biocontrol efficacy on postharvest diseases of fruits was isolated from the wounds of pear fruits; it was identified to be Cryptococcus laurentii (Kufferath) Skinner. The capability of growth of Cryptococcus laurentii, the separation and dryness methods, the safety of C. laurentii and the efficacy of C. laurentii for controlling of postharvest disease of oranges, pears, peaches, strawberries and arbutus berries were studied. The biocontrol mechanism of C. laurentii on postharvest diseases of fruits, the effect of C. laurentii in combination with other control means on postharvest disease of fruits, the efficacy of C. laurentii for reducing natural decay development and quality parameters of fruits and the control efficacy of preharvest use of C. laurentii to postharvest diseases of oranges were studied. The middle model application experiment to test the control efficacy of C. laurentii to postharvest diseases of oranges was done. The results are as followed.The yeasts that have biocontrol efficacy on postharvest diseases of fruits were separated. A strain of yeast that has the highest biocontrol efficacy was got by initial selection and the farther selection. It was proved to be C. laurentii bymorphological and physiological identification.The capability of growth of C. laurentii was studied. The populations of C. laurentii increased quickly in NYDB medium. There was almost no postponing stage in its growth life. The maximum yeast populations were reached with 20h after inoculation at 28℃.Pre-treatment of wounded fruits with C. laurentii, effectively reduced or prevented the development of postharvest diseases of fruits, including: blue mold and gray mold decay of pear, caused by Penicillium expansum and Botrytis cinerea respectively; blue mold and green mold of orange caused by Penicillium italicum and Penicillium digitatum respectively; gray mold and blue mold decay of strawberry caused by Botrytis cinerea and Penicillium expansum respectively; gray mold, blue mold and rhizopus decay of peach, caused by Botrytis cinerea , Penicillium expansum and Rhizopus stolonifer respectively. The concentrations of antagonist had significant effects on biocontrol effectiveness to postharvest diseases of fruits: the higher the concentrations of the antagonist the better the control efficacy.C. laurentii does not inhibit the pathogens by producing antibiotics; the main mode of action of C. laurentii is competitive for nutrients and space. C. laurentii rapidly colonized fruits wounds at low temperature and ambient temperature so as to control pathogens of fruits. Inhibition spore germination of pathogens may be one of the mechanisms of control. The rate of ethylene production was enhanced by the application of C. laurentii. C. laurentii induced the production of resistance enzymes of fruits, including polyphenol oxidase(PPO) and peroxidase(POD). Enhancing the resistance activity of fruits to pathogens may be another mechanism of control to postharvest disease of fruits of C. laurentii.The efficacy of C. laurentii for control to postharvest gray mold decay ofpear was enhanced by the addition of 2% calcium chloride (CaCl2) ; the efficacy of C. laurentii for control of green mold of oranges was improved when combined with 2% sodium bicarbonate (NaHCO3). C.laurentii significantly controlled postharvet gray mold and blue mold of pear, green mold and blue mold of oranges, gray mold of strawber...