Morphological, genetic diversity and symbiotic functioning of rhizobia isolates nodulating cowpea (Vigna unguiculata L. Walp) in soils of Western Kenya and their tolerance to abiotic stress

• Main Authors: Carolyn Odori, Jane Ngaira, Johnson Kinyua, Evans N. Nyaboga
• Format: Article
• Language: English
• Published: Taylor & Francis Group 2020-01-01
• Series: Cogent Food & Agriculture
• Subjects: cowpea; nodulating bacteria; abiotic stress tolerance; genetic diversity; symbiotic efficacy
• Online Access: http://dx.doi.org/10.1080/23311932.2020.1853009

Nitrogen is the most limiting nutrient for growth of most crop plants in sub-Saharan Africa and legume crops largely depend on fixed nitrogen from indigenous nitrogen-fixing bacteria. The identification and symbiotic characterization of indigenous rhizobia is the basis for inoculants formulation for sustainable legume production in the face of climate change. The aim of this study was to evaluate the diversity of indigenous rhizobia responsible for cowpea nodulation in farmers’ fields across three Counties of Western Kenya. The symbiotic performance of abiotic stress-tolerant rhizobia in their homologous cowpea was also assessed. The results showed high genetic variability among the rhizobia isolates based on morphology and ERIC-PCR fingerprinting. Nine indigenous rhizobia isolates tolerant to extreme temperature, salinity and pH were tested for symbiotic efficiency in a glasshouse experiment. The rhizobia isolates were able to efficiently nodulate cowpea and showed wide variations in their symbiotic efficiency (SE). Five isolates (M2bii, B6ii, B2i, V5ii and V11i) showed significantly higher SE (p < 0.001) ranging from 114.6–179.6% compared to the commercial inoculant (CIAT 899) and N supplemented treatment. Further, six isolates with variability in symbiotic efficiencies were subjected to nifH symbiotic gene sequencing and confirmed their identities as Bradyrhizobium and Rhizobium. These isolates have potential for inoculant formulation. The results indicates the existence of indigenous rhizobia isolates which can tolerate environmental stresses and are symbiotically effective and thus can be developed into inoculants to improve the productivity of cowpea in Kenya.