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

Nectarine is a nutritious fruit and is welcomed by consumers. Green mold is its major postharvest disease and could cause big losses. Fruit diseases are usually controlled by application of synthetic fungicides. However, due to the development of fungicides-resistant of pathogens, the environment contamination and human health risks and so on, alternative methods are needed. 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.In this research a strain of bacteria that had the highest biocontrol efficacy was isolated from the nectarine fruits. It was proved to be Bacillus snbtilis(BS-331) by morphology investigation and physiological and biochemical experimentation. For the growth of the strain. the optimum pH and temperature were 5.5 and 30°C, respectively. It could use many carbons as carbon source and organic nitrogen as nitrogen source.The efficacy and biocontrol mechanism of BS-331 for the controlling postharvest diseases of nectarine were studied. The results show that the concentrations of the bacteria cells obviously influenced disease incidence and lesion development of nectarine fruits. When the concentration of bacteria cells was 1×10⁸ CFU/mL. it could control the infectivity of the pathogens. The "in vitro" test proved that pre-treatment of wounded fruits with BS-331 effectively reduced or prevented the development of postharvest disease of green mold of nectarine fruits caused by Penicillium digitatum. Producing antibiotics, competing for nutrition and space were the main mode of action of BS 331 inhibited the pathogens. The "in vivo" test proved that BS-331 induced the production of resistance enzymes of fruits, including peroxidase(POD) and polyphenol oxidase (PPO), reduced the MDA concentration induced by pathogens. Enhancing the resistance activity of fruits to pathogens may be another mechanism of controlling postharvest disease of nectarine fruits of BS-331.The efficacy of BS-331 for controlling postharvest decay of nectarine fruits was enhanced by the addition of some concentration of calcium chloride (CaCl₂); sodium carbonate (Na₂CO₃). The effectivenesses of some low-dose fungicides and natamysin combined with BS-331 in controlling postharvest disease of nectarine fruits were better than either of them.