Symbiotic Efficiency and Genetic Characterization of Rhizobia and Non Rhizobial Endophytes Associated with Cowpea Grown In Semi-Arid Tropics of Kenya

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Date
2021Author
Muindi, Mercy Martha
Muthini, Morris
Njeru, Ezekiel Mugendi
Maingi, John
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Cowpea (Vigna unguiculata (L.) Walp) is an important multipurpose legume crop grown in arid and semi-arid 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 semi-arid areas
of lower Eastern Kenya. Rhizobia trapping and SE experiments were done in the greenhouse while genetic diversity
was evaluated based on 16S rRNA gene sequencing. Twenty morphologically distinct isolates representing
a total of 94 isolates were used for genetic analysis. After 16S rRNA gene sequencing, the isolates closely
resembled bacteria belonging to the genus Rhizobium, Paraburkholderia and non-rhizobial endophytes (Enterobacter,
Strenotrophomonas and Pseudomonas). This study also reports for the first time the presence of an efficient
native cowpea nodulating Beta-Rhizobia (Paraburkholderia phenoliruptrix BR3459a) in Africa. Symbiotic efficiency
of the native rhizobia isolates varied (p < 0.0001) significantly. Remarkably, two isolates, M2 and M3 recorded
higher SE of 82.49 % and 72.76 % respectively compared to the commercial strain Bradyrhizobium sp. USDA 3456
(67.68 %). Our results form an important step in the development of efficient microbial inoculum and sustainable
food production.