| Bacillus spp. has many advantages, such as simple nutritional requirements, fast growth, strong resistance, abundant metabolites, and so on. It has been widely studied and applied in agricultural production. Bacillus spp. is belong to PGPRs, could both control plant diseases and promote plant growth. Alfalfa(Medicago sativa L.) is perennial legume, and known as "king of grass". In this study, Bacillus strains were isolated and conducted a preliminary evaluation for their disease prevention and growth-promoting effects. The results were shown as follows:1. Isolating, screening and identification of Bacillus spp.138 Bacillus strains were isolated from the saline soil of alfalfa rhizosphere, eight strains showed potentials of biocontrol and growth-promoting. According to morphology, physiological and biochemical characteristics and 16 S r DNA sequencing analysis, the isolated strains were identified as: CYY-1 was Bacillus pumilu s, CYY-5 was Bacillus megaterium, CYY-6 was Bacillus licheniformis, CYY-9 was Bacillus cereus, CYY-15 was Bacillus aryabhattai, CYY-20 and CYY-25 were Bacillus subtilis, CYY-42 was Brevibacillus brevis.2. Effect of biocontrol by the Bacillus strainsIn dual culture assay, the 8 strains showed antagonism to the two or more plant pathogenic fungi, which CYY-6, CYY-20, CYY-25 and CYY-42 showed antagonism to Fusarium oxysporum. While, the fermentation broth of the strains could induce deformed growth of mycelia and spores of F. oxysporum. In addition, the strains showed more than 53.96% suppression of alfalfa root rot caused by F. oxysporum in pot experiments.3. Effect of growth-promoting by the Bacillus strainsEight strains could promote the growth of alfalfa in varying degrees through comparing the biomass which including shoot height, root length, shoot and root fresh and dry weight in saline soils. Compared with the control(CK), the strains significantly promoted the alfalfa growth(P < 0.05), especially the strain CYY-9, the biomass were increased by 27.99%, 46.10%, 51.15%, 75.51%, 62.50% and 95.58%, respectively. In addition, the strains CYY-6, CYY-15 and CYY-42 could only promote growth of shootof alfalfa effectively(P < 0.05).4. Characteristics of the Bacillus strainsIn this study, the 8 stains could produce different levels of HCN and carboxymethyl cellulose, synthesize siderophore and IAA, phosphate solubilization, and have ACC deaminase activity. The produce HCN capability of the strains CYY-1, CYY-6 and CYY-20 were the strongest in all isolates. The strain CYY-25 could produce the most carboxymethyl cellulose, and the cellulase activity is 0.364 IU/m L. The ability of synthesize siderophore of CYY-9 was the highest, and the value was 0.813. With the concentration of L-Trp increased, the IAA syntheses were increased significantly by all strains(P < 0.05). When there was not L-Trp in the medium, the strains CYY-1, CYY-15 and CYY-20 could produce amounts of IAA, and the others could hardly synthesize IAA. With the L-Trp concentrations of 200 and 500 μg/m L, the IAA synthesis value of the highest strain CYY-9 was 6.76 and 14.46 μg/m L·OD600, respectively.The ability of phosphate solubilization of the strain CYY-9 was stronger than the other strains with value of 470 μg/m L. In addition, the strongest of ACC deaminase activities were strains CYY-1, CYY-5, CYY-9, CYY-20 and CYY-25. |
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