Nitrogen-Fixing and Phosphate Solubilizing Potentials of Rhizobacteria from the Rhizosphere of Two Cassava Varieties in Iyamho Community

Abstract

Microorganisms in close association with the roots of plants can enhance plant growth, through nitrogen fixation (NF) and phosphorus solubilization (PS). Although the type of microbes in close association with different plants varies, their population and genetic capabilities is affected by several factors. Therefore, in this study, the plant growth promoting properties of rhizobacteria present in the rhizosphere of two cassava varieties (Sweet cassava US, bitter cassava ST) indigenous to Iyamho community was explored.   The samples were analyzed for total culturable heterotrophic bacteria community and the obtained isolates were screened for NF and PS abilities using a semi-solid N-free medium and Pikovaskya agar respectively. The bacterial population in both agar medium varied, however, the bacterial counts on Luria Bertani (3.67 x 105, 3.35 x 106) was higher than  Nutrient agar (2.73 x 105, 2.68 x 105) after incubation for 24 hours at 37oC  for sweet and bitter cassava rhizosp here respectively. Also, isolates from sweet cassava had the highest bacteria count in both Nutrient agar and Luria Bertani agar. A total of sixteen isolates were obtained, six phosphate solubilizers, five nitrogen fixers, and five without traits for either NF or PS. The Gram-negative bacterial group was more dominant across all isolates while the dominant genus was Bacillus. This study indicates that the nitrogen fixers and phosphate solubilizers are major constituents of the rhizomicrobe of cassava plants although the distribution varies across cassava varieties. However, sweet cassava rhizosphere harbored more nitrogen-fixing bacteria while both varieties had the same amount of phosphate solubilizing rhizobacteria.