Isolation and Enumeration of Bradyrhizobium Species Dwelling In the Root Nodules of Soybean Plant

Abstract

Biological Nitrogen fixation is one of the important aspects of organic agriculture gaining considerable attention globally. Information about the number of viable indigenous Bradyrhizobia in soils planted with legumes and their capacity to nodulate is a valuable tool in developing strategies to improve biological nitrogen fixation. Such strategies could potentially lead to increased soybean yields at low cost. This study was conducted to isolate and enumerate Bradyrizobium species dwelling in the root nodule of soybean plant using Bradyrhizobium japonicum selective medium (BJSM). Twenty (20) strains of Bradyrizobium species were isolated from the root nodules of soybean plants harvested from Ahmadu Bello University farm site, located at Bomo district of Sabongari local government area, Kaduna State, Nigeria. This was achieved using the streak method of isolation on BJSM. Ninety percent (18) of these isolates were confirmed as Bradyrizobium species using the plant infection test as they were able to nodulate the roots of soybean plants. The enumeration of the indigenous Bradyrizobium species gave a count ranging from 2.07x105 - 4.0x106 CFU/mL. Thus, the number of Bradyrhizobia obtained in the soil of this study is sufficient to achieve satisfactory results on nodulation and nitrogen fixation. Key words: Soybean, Bradyrhizobium species, Nodulation, Nitrogen fixation