Postharvest Biological Control Of Lingwu Long Jujube Fruits By Yeast

Biological control of postharvest diseases in fruits and vegetables has been a potential new technology.The aim of this research is to isolate and screen out the effective antagonist against the main pathogens of Lingwu Long Jujube fruits,identify it,study its biological characteristics.The inhibition effects and their proper dynamics were evaluated after the antagonist was screened.Some conclusions were drawn as following:1.Isolating and identification of main pathogensFive main pathogens were isolated from the surface of fruits,wounds,leaves,and rhizosphere soil.The isolations of five pathogens were:Rhizopus spp.,Penicillium spp., Aspergillus spp.,Alternaria spp.and Fusarium spp.,respectively.The pathopoiesis of five pathogens were confirmed according to Koch's postulate.2.Isolating and screening of antagonistic yeastThree bacteria isolates and six yeast isolates were selected from the surfaces and wounds of Lingwu Long Jujube fruits.A yeast isolate named Y-6,was tested for antagonistic activity against five main pathogens in Lingwu Long Jujube fruits.3.Identification of antagonistic yeastIn order to further study its characters,the strain Y-6 was needed to be identified to genus.According to morphological and physiological experiments,it belonged to Kloeckera apiculata,Kloeckera spp..4.Biological characteristics of antagonistic yeastThe growth curve of Y-6 was divided into lag phase,logarithmic growth phase, stationary phase and decline phase.The suitable temperature range was 20℃～30℃,and the most suitable was 28℃;The suitable pH range was pH5～7,and the most suitable was pH6;The most suitable carbon source was glucose;The most suitable nitrogen source were peptone and yeast extract;The most effective mineral salts were K₂HPO₄ and KH₂PO₄.5.Study on inhibition effect of Y-6 on main pathogensThe effects of antagonist increased with the increase of antagonist cell population when the antagonist at the concentration of 1.0×10⁶～1.0×10⁸CFU/mL.Fruits were treated with antagonist suspension at 1.0×10⁸CFU/mL at various time intervals(48h,24h,2h,0h) before and after challenge-inoculated with pathogenic spore suspension at 1.0×10⁴spores/mL.The result of inoculation-time test showed that the efficacy of biocontrol increased significantly with the time antagonist applied before pathogen inoculated.6.Study on antagonistic mechanism of Y-6The antagonistic mechanism of the strain Y-6 activity did not involve in the production antifungal substances,since supematant solution and treatment liquid did not inhibit the pathogens.The antagonistic mechanism of the strain Y-6 may involve the nutrition and spatial competition,since the inhibition effect of the cell suspending liquid was stronger than the original fluid.Y-6 could change the activities of phenoloxidase, peroxidase and superoxide dimutese,and increase the antifungal activities of long jujubes.