Screening and isolated of plant growth promoting rhizobacteria <i>Azotobacter</i> sp. from maize rhizosphere

<p>Recently, the use of a large amount of chemical fertilizers has caused environmental pollution. Therefore, to protect the environment and develop agricultural practices, organic agricultural practices have been resurgent. To develop the organic agricultural practices, there must be the benefit of microorganisms. <em>Azotobacter</em> species have the multi-functional plant growth-promoting activities, for example, N₂ fixation, phosphate solubilization, indole-acetic acid (IAA) production, siderophore production and biocontrol ability against plant pathogens. In this paper, <em>Azotobacter</em> strains had been isolated from maize rhizosphere and their plant growth promoting activities had been studied. The nitrogenase activity varied between 31.3–167.4 n moles C₂H₂ produced mg⁻¹ protein h⁻¹. Tests of IAA production showed positive results in all the isolates. The plate assay for phosphate solubilization activity by Pikovskaya (PVK) agar showed seventeen isolates could solubilize phosphate. Isolate P-7 showed the highest plant growth-promoting activity and seed germination of maize by seed inoculation with <em>Azotobacter</em> strains. On the basis of the morphological characters, biochemical characters and 16S rRNA gene sequence analysis, isolate P-7 was identified as <em>Azotobacter</em> <em>chroococcum</em>. This study may provide additional knowledge on the PGPR of <em>Azotobacter</em> sp. and will be used in future research on the field tests of maize.</p>