| In this paper, the endophytic bacteria were isolated from soybean nodules at full-bloom stage collected in defferent places of Sichuan Basin by streak plate method.16S rDNA PCR,16S DNA PCR-RFLP and 16S rDNA sequence analysis were performed to explore the genetic diversity of the endophytic bacteria and determine the phylogenetic position. based on the plant growth promoting characteristics, such as IAA producing ability, siderophore producing capacity, phosphorus dissolving ability and nitrogen fixing capacity, using soybean as target plant in pot experiment, the Plant Growth Promoting Bacteria (PGPB) were screened. Furthermore, pea, broad bean and corn were used as target plants in pot experiments; and the PGP ability of candidate bacteria was performed.The results were as the follows:1. A total of 130 putative endophytic bacteria were isolated from the root nodules of Soybean in Sichuan Basin, results of 16S rDNA PCR-RFLP analysis showed that all the strains formed 81 genotypes, and 5 genetic clusters were performed, which revealed the genetic diversity of these bacteria. Except DA13-1, the other bacteria belonged to 4 genetic groups, and group I was the largest one, containing 62 strains, occupied 47.7%, group IV, III and II were consisted of 40,17and 10 strains.2. Forty strains were chosen and analyzed 16S rDNA sequences, and the phylogenic tree was constructed by MEGA6.0. The results showed that these strains belonged to genus Bacillus, Pseudomonas, Bradyrhizobium, Enterobacter, and Sinorhizobium. Strains belonged to genus Bacillus was the dominant one, including six species, i.e. B. subtilis, B. aryabhattai, B. methylotrophicus, B. simplex, B.idriensi and B. pumilus; and secondly, the predominant strains were genus Sinorhizobium and Pseudomonas.3. Using soybean as the target plant in pot experiment,12 PGPB candidate strains were screened preliminary. Further studies showed that all the strains had IAA producing ability, and the IAA concentration reached 0.353-32.404?g/mL; Enterobacter sp. D13-3 had the highest IAA producing ability, and IAA content was 32.404±0.002 ?g/mL; and the second one was B.methylotrophicus DA8-1, IAA content was 11.282±0.006 ?g/mL. There were seven strains had siderophore producing ability and the siderophore activity unit was 7.35%-34.31%; DA13-1, DB30-2 and DB1-3 had higher siderophore producing ability, the siderophore activity unit was 34.31%,32.35%and 31.37%, respectively. Furthermore,11 strains were able to solubilize phosphate and the available phosphorus was 4.26-10.6?g/mL in the liquid culture when adding 5g/L of Ca3(PO4)2. There were 6 strains free-living nitrogen fixing capacity, including three rhizobial strains, Enterobacter sp. DA10-3, Bacillus methylotrophicus DA8-land Pseudomonas monteilii DB19-3.4. Simultaneously, Pea, broad bean and corn as target plants, together with twelve selected bacteria were used to confirm the PGB capacity in pot experiments. The result displayed that most strains had plant growth promoting effect on the three target plants. Of them, DA8-1(B.methylotrophicus) and DA16-5 (B.methylotrophicus) had the best growth promoting effect. Strain DA8-1 had good growth-promoting effect on soybean, pea and broad bean, and strain DA16-5 had good growth-promoting effect on soybean, broad bean and corn. The soil nutrients had also been increased after inoculation of DA8-1 and DA16-5, the soil available phosphorus, soil available potassium, soil available nitrogen and organic matter content in the pot experiment increased 29.4%,30.7%,30.1% and 11.2%. |
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