Profiling Rhizosphere Microbes on the Root of Maize (Zea mays) Planted in an Alfisol for Selection as Plant Growth Promoting Rhizobacteria (PGPR)

Maize (Zea mays L. Merill) root rhizosphere, being a metabolite-enriched niche was profiled with the objective of isolating Plant Growth Promoting Rhizobacteria (PGPR) for bio-fertilizer production. Isolation was carried out from the root surface and rhizosphere soil samples of the plant using standard procedures. Cultural, physiological and biochemical procedures were used to identify the isolates. Eighty (80) isolates obtained were screened for growth promoting attributes and sixteen (16) representative isolates selected, and further identified using molecular methods by sequencing of their 16S rDNA gene. Sixty three percent of the characterized organisms exhibited sequence homology level equal or greater than 90% with those of the gene bank. Microorganisms with pathogenic characteristics were eliminated. As a result of this, Bacillus thuringiensis, Pseudomonas putida and Klebsiella varricola selected, were further screened in vitro for Indole acetic acid (IAA), Gibberellic acid (GA) and Cytokinin production using standard assay methods. Klebsiella varricola produced 19.697 mg/L of GA, 0.348 mg/L of IAA and 1.804 mg/L of Cytokinin. Pseudomonas putida had 2.693 mg/L of GA, 0.152 mg/L and of IAA and 5.066 mg/L of Cytokinin in solution while Bacillus thuringiensis excreted 15.091 mg/L, 0.132 mg/L and 2.410 mg/L of GA, IAA and Cytokinin respectively. The 3 PGPR are considered suitable for biofertilization programme.