The Primary Research Of Ginkgo Endophytic Bacterial Antagonists Against White Radish Soft Rot Disease

For evaluating the potential function of Ginkgo's endophytic bacteria to control plant diseases, 154 bacterial strains were isolated from surface-sterilized branches, petioles and leaves of Ginkgo, which collected from Hangzhou, Zhejiang, Taian, Shandong, Zhengzhou, Henan, Nanping and Fuzhou Fujian, and tested to against plant pathogenic bacteria. Among the 154 bacterial isolates, 57 isolates could inhibit the growth of Pectobacterium carotovorum subsp. carotovorum, Clavibacter michiganensis subsp. michiganensis, Pseudomonas syringae pv. tomato, Acidovorax avenae subsp. citrulli, Xanthomonas oryzae pv. oryzicola and P. syringae pv. averrhoii. Meanwhile, 65 bacterial endophytes suppressed the pathogen P. carotovorum subsp. carotovorum under plate assay in vitro which the maximum radius of inhibition zones was 6.75 mm.Through test in vivo, 2 strains, hy11 and zy2, among the isolates were selected as they could effectively inhibit the white radish soft rot by needle puncture inoculating with pathogens. The disease of the white radish coinoculated with endophytic bacteria and pathogens were delayed and the control efficacies of hy11 and zy2 were 77.8% and 50% respectively after inoculating 7 d. Inoculating white radish with endophytic bacteria, the prevalence of seedlings soft rot was reduced and seedlings were not easy to damping off when they infected. The control effects of the 2 strains were 77.8% and 50% respectively. Besides, the 2 strains could obviously promote the growth of white radish seedlings. Based on the morphological, physiological, biochemical characteristics and 16S rDNA and gyrB gene sequences analysis, the 2 strains were identified as Bacillus amyloliquefaciens.For proving endophytic colonization ability of strain hy11, the strain hy11-gfp labeled with gfp and kan genes was constructed. Inoculating the labeled strain to Ginkgo leaves by rub and spray inoculation methods, the endophytic clone numbers of hy11-gfp were increased in the early stagefirst and then decreased to a stable number, about 5.0×10~4 cfu/(g.fw), in 40 d. Pouring hy11-gfp suspension in the rhizosphere surface of white radish seedlings, the hy11-gfp clone numbers of inside roots, stems and leaves were increased at the early stage and then decreased. After inoculating 40 d, the label strain still could be isolated from the plant tissues.In this study, 6 strains containing aiiA gene were selected from the 154 isolates by PCR using aiiA gene primers. These strains had not any inhibiting activity to P. carotovorum subsp. carotovorum under plate assay in vitro, but could partially control white radish soft rot of tubers and seedlings. The control effects of strain x3 and gbb5 selected from 6 strains were both above 50%. Meanwhile, the 2 strains could promote the seedling growth observably. According to 16S rDNA sequences analysis, the strain x3 was identified as B. thuringiensis and the gbb5 as B. cereus.