Abstract
The significance of cowpea (Vigna unguiculata L. Walp) as nutritional, economic and a soil fertility promoter had already been elucidated by many researchers. The present work was aimed at isolation and characterization of rhizobial and non-rhizobial endophytes of cowpea nodules recovered from smallholder farms in northern Nigeria. The study soils were analyzed and found to have varying physical and chemical characteristics. Nine (75 %) of the soil samples were sandy loam while the others included sand loam, sand and clay loam each. The pH (water) of the soils ranged from moderately acidic to neutral. The fertility status of the soils in respect to total nitrogen (%), (phosphorus mg kg-1) potassium (Exc K), and organic carbon (%) varied among sites. Each of the 40 nodular endophytes was isolated using yeast mannitol agar and phenotypically characterized using 14 assays (5-growth, 4-sugar fementation, 5-temperature courses). In all, 35 % of the isolates tested positive for the 14 assays. All isolates grew in nutrient agar, King’s B agar; and 30 °C and 40 °C. Hierarchical Cluster Analysis (HCA) indicated diversity and similarities among isolates from same and different localities. Soil origin, its features or conditions did not appear to determine the phenotypes of the bacterial isolates. Growth of some of the isolates on Pseudomonas selective agar suggests that bacteria resident in cowpea nodules included at least rhizobia and pseudomonads flora.
Keywords: Legumes, Pseudomonas, Rhizobia, Soil, Sub-saharan Africa
