Screening Of Pseudomonas Fluorescens And Biocontrol Of Alternaria Alternata

Pseudomonas fluorescences is plant growth-promoting rhizobacteria (PGPR).Most Pseudomonas fluorescences isolated from plant rhizosphere can play an important role on biological control of plant diseases and stimulation plant growth.Therefore,it is potential for Pseudomonas fluorescences to suppress plant diseases. Using Pseudomonas fluorescence 16S-23SrRNA primers, A total 156 of water-soluble fluorescence strains were isolated from 448 soil samples collected from rhizosphere of tobacco in the Heilongjiang Tobacco Research Institute was amplified by clony PCR. 48 strains which amplified 550bp specific PCR product were screened from 156 isolates tested, and the PCR primers of 2,4-DAPG,Prn,Plt and PCA gene were used to amplify these obtained 48 isolates, one strain which could produce 2,4-DAPG and PCA was screened and named as PF7-5. The bioinformatics analysis results found that 2,4-DAPG of PF7-5 share high homology(96%) with that of Pseudomonas fluorescens strain F113 and the homology of PCA from PF7-5 was 89% with Pseudomonas fluorescens strain S2P5.The Studies on the culture medium components and fermentation conditions of PF7-5 suggested the optimum culture medium should contain peptone 25g, glucose 6.2g, K2HPO4·3H2O 1.5g,MgSO4·7H2O 2g, pH 7.0 in the total volume of 1000mL medium. The capacity of antibiotic substances of PF7-5 will be the on the condition of 26℃for 72h. The effects of heat, pH and UV on the stability of antifungal substances showed antifungal substances were relative stabile.The influence of PF7-5 on the hyphal and spore of tobacco brown spot were studied by means of optics microscopy techniques, the results confirmed that hyphal growth of Alternaria altrnata was significantly inhibited, and the spores bourgeon of the pathogen were delayed and inhibied.The performance were including twist of hyphae, necrosis of the hyphal wall,concentration and leakage of the cytoplasma.The results of colonization and disease preventiong of PF7-5 in greenhouse showed that PF7-5 strain had good leaf and root colonization capacity, and it has a strong antagonism action to Alternaria. The control effect of this strain was not less than 50 percent for the control of tobacco brown spot.