The Study Of Biocontrol And Mechanism Of Action On Postharvest Diseases Of Circus Fruits By Bacillus Subtilis

As public's growing concern for the human health conditions and the environmental pollution associated with pesticide usage in orchards, there is a great need for alternative approaches. Biological control using antagonists, as a novel technology fitting the current of sustainable agriculture, has been proved to be one of the most promising alternatives and attracted increasing attention from scientists. A strain of bacteria that have high biocontrol efficacy on postharvest diseases of green mold and blue mold on circus fruits was isolated and identified to be Bacillus subtilis. The character of BS-Z, the optimization of the culture medium and culture conditions of BS-Z, a Kinetic Model of Batch Fermentation by Bacillus subtilis, and the efficacy of BS-Z for the controlling of postharvest diseases of citrus were studied. The biocontrol mechanism of BS-Z on postharvest diseases of citrus fruits, the effect of BS-Z in combination with other control means on postharvest diseases of fruits, the efficacy of BS-Z for reducing the natural decay development and quality parameters of fruits were studied. The results are as followed.(1) The bacterias that have biocontrol efficacy on postharvest diseases of fruits were separated. A strain of bacteria that have the highest biocontrol efficacy was got by initial selection and the farther selection. It was proved to be Bacillus subtilis(BS-Z) by VITEK 32 Automicrobic System(bioMerieux).(2) Pre-treatment of wounded fruits with BS-Z effectively reduced or prevented the development of postharvest diseases of blue mold and green mold on citrus fruits caused by Penicillium italicum and Penicillium digitatum. The concentrations of antagonist had significant effects on biocontrol effectiveness to postharvest diseases of fruits.(3) BS-Z inhibit the pathogens by producing antibiotics;Competitive for nutrients and space is the main mode of action of BS-Z. BS-Z induced the production of resistance enzymes of fruits, including peroxidase(POD) and SOD, reduced the MDA concentration induced by pathogens. Enhancing the resistance activity of fruits to pathogens may be another mechanism of control to postharvest disease of fruits of BS-Z.(4) The efficacy of BS-Z for control to postharvest decay of citrus fruits was enhanced by the addition of some concentration of calcium chloride (CaCl₂);sodium bicarbonate (NaHCO 3 ), MgCb . The effectiveness of some low-dose fungicide combined with BS-Z in controlling postharvest diease of citrus fruits was better than either of them.( 5 ) BS-Z significantly reduced the natural development of decay on citrus fruits after storage in normal temperature of 50 days. The quality parameters of fruits treated with antagonist were similar to those of control fruits, which suggested that BS-Z did not impair quality parameters of fruits.( 6 ) Optimized the culture medium and culture conditions for the BS-Z permentation, which enhanced the concentraion of BS-Z greatly.( 7 ) The fermentation process of Bacillus subtilis, was studied in a 70-L batch system. A simple model was proposed using the Logistic equation for growth, the Luedeking-Piret equation for antifungal substance production and Luedeking-Piret-like equations for substrate consumption, respectively. And the fit value is 0.9934, 0.8312, 0.9455, respectively. The model appeared to provide a reasonable description for each parameter during the growth phase.