| The endophytic bacteria living inside plants can promote plant growth, which can be used to develop microbial fertilizer, with the advantages promotion plant growth, no pollution, and low cost, etc.. Pongamia pinnata is a kind of biomass energy plants, and has resistant capacity to high temperature, drought, barren, and salt, etc. In this paper, Pongamia pinnata were collected from mangrove in Wenchang, Hainan province, and the endophytic bacteria in roots were isolated. BOXAIR-PCR and 16S rDNA sequence analysis was used to study their diversity and phylogeny. Then, Salkowski colorimetric method was used to determine IAA production; Molybdenum antimony colorimetric method was used to determine inorganic phosphorus dissolving ability; modified CAS method was used to detect siderophore producing capacity; the potassium persulfate oxidation method was used to determine the nitrogen fixing ability. Then, the plant promote growth ability was evaluated by pot experiments. The results were as follows:1. A total of 50 endophytic bacteria strains were isolated from roots of Pongamia pinnata, BOXAIR-PCR and phylogenetic analysis of 16S rDNA sequences showed that the endophytic bacteria had very high genetic diversity. BOXAIR-PCR showed that 50 endophytic bacteria were divided into six genetic groups at the level of 82% similarity, and group I was the largest one containing 58% strains; however, there were 7 isolates formed group individually.2. In accordance with BOXAIR-PCR analysis,13 representative strains were selected and the phylogenic tree was constructed by 16S rDNA sequences. The results suggested that, the strains were classified into genus Bacillus, Lysinibacillus, Paenibacillus, Corynebacterium, Burkholderia and Ochrobactrum, respectively, which revealed the genetic diversity of endophytic bacteria isolated from Pongamia roots. Strains G3, G16 and G17 belonged to Bacillus aryabhattai, strains G4 and G6 belonged to Bacillus thuringiensis, strains G10 and G26 belonged to Ochrobactrum anthropi, strain G9, G14, G35, G36, G39 and G50 belonged to Burkholderia anthina, Paenibacillus glycanilyticus, Corynebacterium callunae, Lysinibacillus fusiformis, Bacillus subtilis, and Bacillus cereus, respectively.3. Furthermore, the capacity of IAA production, phosphate-solubilization, siderphores production and nitrogen fixation of the representative endophytic bacteria were obtained through the bioactivity assay. The results showed that all of representative strains could produce IAA with amount of 17.55-59.55μg/mL, and strain G16 had the highest IAA content (59.55μg/mL). There were 76.9% tested strains had siderophore producing ability, and the siderophore content ranged from 6.00 to 104.50μg/mL; and strain G26 produced highest amount of siderophore (104,50μg/mL). Strain G9 was the only one with inorganic phosphorus solubilizing ability, and the phosphorus amount was 4.87μg/mL. There were four representative strains (G94, G14, GlOand G26) could fix nitrogen, and the total nitrogen was 1.57-6.84μg/mL, and strains G10 had the highest nitrogen fixing ability, the total nitrogen in liquid culture was 6.84μg/mL.4. Moreover, five siderophore-producing endophytic bacteria, i.e. G3, G9, G]0, G17, and G26, were screened and their siderophore yield ranged 41.50 to 104.50μg/mL. Then, peanut seeds were cultivated in calcareous purple soil by pot experiment in greenhouse, and the tested strains were used as inoculants, which was carried out to evaluate the growth-promoting efficient of these 5 strains. The results indicated that inoculation of five strains increased the total plant N, P, K, and Fe, and increased the plant dry weight. The plant dry weight increased 6.78 and 23.72%; the total plant N increased 96.94% and 76.53%, the total plant P increased 17.71%and 20.83%, the total plant K increased 16.15% and 14.91%; the total Fe content in the peanut plant increased 32.14 and 73.45%, respectively, after inoculating strains G10 and G26, which showed that these strains had significant effects on plant growth-promotion. |
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