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Various rhizobacteria strains are isolated and tested worldwide for their plant growth promoting activities. A strain is said to be a plant growth promoter if it has the ability to influence plant growth directly or indirectly. Though the main focus has always been to realize the plant growth promoting traits of rhizobacteria and use them as biofertilizers, but the disadvantages or deleterious effects of such plant growth promoting rhizobacteria (PGPR) if any have also been ignored to a greater extent. The present study deals with the characterization of both promoting as well as deleterious activities of an isolated strain of Pseudomonas aeruginosa on plants. The bacterium was isolated from the soil of the college campus of Babasaheb Bhimrao Ambedkar University, Lucknow, Uttar Pradesh and was characterized as P. aeruginosa by various positive biochemical tests such as oxidase, catalase, citrate tests and confirmed by MALDI-TOF-MS. Its growth as well as IAA producing ability at different salt (NaCl) concentrations was tested. Tests examining HCN, Ammonia and siderophore production, flocculation ability, phosphate and zinc solubilization by the strain were carried out. Its anti-microbial property was tested against three phytopathogenic fungi: Fusarium solani, Aspergillus niger and Curvularia lunata and two bacterial strains - Klebsiella pneumoniae and E. coli. Its effect over seed germination of Triticum aestivum and Zea mays was inspected in plates as well as in pots. The strain showed a great potential as a plant growth promoter growing up to 10% NaCl concentration and producing considerable amount of IAA upto 8% NaCl concentration. It showed antagonistic nature against the three phytopathogenic fungi, solubilized phosphate and produced siderophore and NH3. Though supernatant of the bacterial culture did not show any deleterious effect over seed (of the test plants T. aestivum and Z. mays) germination but the seeds inoculated with the strain itself, failed to germinate. The seed turned dormant and grew a pale brown color showing bacterial growth over it. Thus it maybe concluded that the isolated strain of P. aeruginosa has abilities to both promote and at the same time inhibit plant growth (by inhibiting seed germination).
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