| This research aimed at isolating and screening of antagonistic actinomycetes with great activity to plant pathogens,searching for the source of new agri-antibiotics, studying and analyzing the antibacterial substances produced by them preliminarily. (1)In order to improve the efficiency of isolating actinomycetes from soil and solve the problem of contamination by fungus and bacteria when actinomycetes isolated and cultivated,basing on the predecessor's researchs,we developed a suitable method to isolate actinomycetes selectively:6% yeast extract and 0.05% SDS ( 5mmol/L phosphate buffer) pretreated the soil suspension jointly after the collected soil samples are air-dried at 28℃for 10 days as soon as possible.Then,with the method of plate dilution the colonies of actinomycetes is picked out from the medium after the soil suspension diluted with water is inoculated on the corn meal agar and soybean farina agar medium which were both added with 250mg K2Cr2O7/L medium for 7 days. (2)In this study,360 strains of actinomycetes were isolated from 20 mixed soil samples which collected from various areas in the Zhouzhi Nature Reserve of Shanxi province. (3)During the selection of antagonistic Actinomycetes, a new genetically stable actinomycetes strain S-5210 which had strong antagonistic to many plant pathogens was selected through agar plate experiment,fermental filtrate plate experiment, ex vivo leaf experiment,pot experiment and single spore isolation.This selection model through both in vivo and ex vivo method of plant could not only reduce the workload and increase the selection level,but also prove the stable capability of the antibiotic selected by this model. (4)According to its morphological, cultural, and physiological biochemical characteristics of S-5210, it was designated to streptomyces and lavendlarectus preliminarily. (5)The strongest active substances of S-5210 had been better separated and extracted from fermented liquid through deposition by CaCl2 added with KH2PO4, extraction by ethyl acetate, elution by the iron exchange chromatography and the analytical and separate technique by high performance liquid chromatography (HPLC). (6)The study was made on the S-5210 crude extract's physical and chemical properties.The results showed that this antibiotic was alkaline and water-solubility,it could be dissolved in organic solvent such as methanol, ethanol, acetone, n-butanol, ethyl acetate, chloroform,benzene,but was indiscerptible in hexane,aether,petroleum ether and so on. It was relatively stable under the weakly acid, neutral conditions and middle temperature.Also it was store-resistant. (7)The crude extract of S-5210 had a selective inhibition to bacteria and a wide-range of inhibition to fungal pathogens.Through indoor experiment, it had a strong antagonistic action to 12 pathogens.To obligatory pathogens like Pseudoperonospron cubensis, it could not only hold back the infection of hypha,but also heal the spot where infected by hypha. (8)The study on mechanism of action showed that the crude extract of S-5210 had a strong inhibition of the mycelia growth and spore germination which led to some abnormal growth such as the twisted and inflated mycelia, the abnormal increased branching, the broken mycelia wall and leakage of cytoplasm from hyphal tips.Alao the spores and the rate of germination were decreased, the germ tube was malformed in shape et al.The pathogenicity of hypha and spore was weakened.
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