Symbiotic efficiency and genetic characterization of bacteria associated with cowpea genotypes grown in semiarid tropics of Kenya

<p>Cowpea (<i>Vigna unguiculata</i> (L.) Walp) is an important multipurpose legume crop grown in arid semiarid areas of sub-Saharan Africa. The crop associates with a wide diversity of high ecological value rhizobia bacteria, improving biological soil fertility and crop production. Here, we evaluated the symbiotic efficiency (SE) and genetic diversity of native rhizobia isolated from root nodules of cowpea genotypes cultivated in semiarid areas of Kenya.  Rhizobia trapping and SE experiments were done in the greenhouse while genetic diversity was evaluated based on 16S rRNA gene sequencing. Ninety four bacterial nodule isolates were purified from root nodules and placed into 20 groups based on morphological characteristics. SE of the native isolates varied (<i>p</i>&lt;0.0001) significantly. Remarkably, two isolates, M2 and M3 recorded higher SE of 82.49 % and 72.76 % respectively compared to the commercial strain <i>Bradyrhizobia</i> sp. USDA 3456 (67.68 %). The isolates closely resembled bacteria belonging to the genus <i>Rhizobium</i> and non-rhizobial endophytes <i>Enterobacter</i>, <i>Strenotrophomonas</i>, <i>Pseudomonas</i>, and <i>Paraburkholderia.</i> For the first time, we report the presence of an efficient native nodule isolate <i>Paraburkholderia phenoliruptrix</i> BR3459a in Kenya. Our results form an important step towards the development of efficient microbial inocula which are pertinent for sustainable food production in African agriecosystems.</p>