ABSTRACT

Bacteria in the rhizosphere that can penetrate plant tissues are referred to as endophytic bacteria. Numerous studies have explored the presence of bacteria in various plant parts such as nodules, roots, stems, leaves, flowers, and seeds. Plant growth promoting bacteria are generating interests in the agricultural industry as a promising alternative to traditional chemical fertilizers, however much of the focus has been on endophytic bacteria. This study was aimed at isolating and identifying the endophytic bacteria associated with cowpea root nodules. Standard bacteriological methods were used to determine the total bacterial count using pour plate methods after serial dilution. The bacterial isolates were characterized and identified using morphological and biochemical methods. The distribution of the isolates was evaluated using statistical method. The bacterial population obtained from the root nodules ranged from 4.87 log₁₀ cfu/g, to 5.12 log₁₀ cfu/g. Through standard cultural and morphological characteristics, the isolates in this study were identified as Bacillus subtilis, Bacillus cereus, Pseudomonas sp., Acetobacter sp., Rhizobium sp. and Micrococcus sp. All isolates obtained in this study were positive for indole acetic acid (IAA). The phosphate solubility test demonstrated that all isolates were phosphate solubilizers, with Pseudomonas and Rhizobium sp. exhibiting halozones of 15mm and 9mm respectively. The shoot height, shoot width and taproot width of the cowpea plants treated with Pseudomonas sp. + Rhizobium sp. showed a higher mean of 6.3cm, 0.3cm and 0.2cm respectively compared to the cowpea plants treated with Pseudomonas sp. and Rhizobium sp. only, indicating the synergism of the endophytic bacteria isolates to improve the shoot length and width of leguminous plants. The results of this study provide evidence of the relation of growth promotion in plants by endophytic bacteria. The inherent plant growth promoting properties of these bacterial endophytes are important factors for the development of sustainable agricultural system, especially necessary for agriculture in Edo state and Nigeria in general.