Isolation of Plant Hormone (Indole-3-Acetic Acid - IAA) Producing Rhizobacteria and Study on Their Effects on Maize Seedling
18 rhizobacteria were isolated from various rhizospheric soils in Mandalay region, Myanmar and some of their biochemical characteristics were studied. Among them, 4 isolates belonged to Bacillus spp. and another 5 strains were recognized as Serratia spp. All 18 isolates were screened for indole-3-acetic acid (IAA) production and quantitative determination of IAA was done for all strains by UV-Vis spectrophotometer with 2 days interval during 10 days incubation. All isolates had different optimum IAA production periods and strain R1 was the best IAA producer strain with 121.1 ppm. It was observed that Bacillus spp. produced IAA ranging from 53.1 ppm to 71.1 ppm optimally and Serratia spp. can be regarded as poor IAA producer strains. Among these 18 strains, four of the best IAA producers (R1, R3, R5, R8) were selected for further study on maize plant and their activities of nitrogen fixation were also detected by plate screening method. Seed germination rate was studied with eight types of treatment and the treatment systems with isolates cannot show distinct positive effect on seed germination rate. At 20th day after sowing, dry root weight and fresh root weight, root length, number of adventitious roots, dry shoot weight and fresh shoot weight and shoot height were measured. In pot trial experiment, treatment R1 significantly increased the fresh shoot weight, shoot height and dry shoot weight whereas treatment R3 significantly increased fresh root weight, root length, dry root weight and number of adventitious roots and all treatments with bacterial isolates showed plant growth promotion than the control systems.
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