Author(s)

Damba Yahaya^1,2, Nicholas Denwar³, Mustapha Mohammed^4*, Matthew W. Blair^1*

¹Department of Agricultural and Environmental Sciences, Tennessee State University, Nashville, TN, USA.
²Department of Biotechnology, University for Development Studies, Tamale, Ghana.
³Council for Scientific and Industrial Research, Savannah Agricultural Research Institute, Tamale, Ghana.
⁴Department of Crop Sciences, Tshwane University of Technology, Pretoria, South Africa.

To explore the variations in symbiotic N₂ fixation and water use efficiency in cowpea, this study evaluated 25 USDA cowpea genotypes subjected to drought under field conditions at two locations (Kpachi and Woribogu) in the Northern region of Ghana. The ¹⁵N and ¹³C natural abundance techniques were respectively used to assess N₂ fixation and water use efficiency. The test genotypes elicited high symbiotic dependence in association with indigenous rhizobia, deriving between 55% and 98% of their N requirements from symbiosis. Consequently, the amounts of N-fixed by the genotypes showed remarkable variations, with values ranging from 37 kg·N-fixed·ha^-1 to 337 kg·N-fixed·ha^-1. Most genotypes elicited contrasting symbiotic performance between locations, a finding that highlights the effect of complex host/soil microbiome compatibility on the efficiency of the cowpea-rhizobia symbiosis. The test genotypes showed marked variations in water use efficiency, with most of the genotypes recording higher δ¹³C values when planted at Kpachi. Despite the high symbiotic dependence, the grain yield of the test cowpeas was low due to the imposed drought, and ranged from 56 kg/ha to 556 kg/ha at Kpachi, and 143 kg/ha to 748 kg/ha at Woribogu. The fact that some genotypes could grow and produce grain yields of 627 - 748 kg/ha under drought imposition is an important trait that could be tapped for further improvement of cowpea. These findings highlight the importance of the cowpea-rhizobia symbiosis and enhanced water relations in the crop’s wider adaptation to adverse edaphoclimatic conditions.

Drought, Cowpea, Carbon Isotope Discrimination, Nitrogen Fixation, Grain Yield

Yahaya, D. , Denwar, N. , Mohammed, M. and Blair, M. (2019) Screening Cowpea (Vigna unguiculata (L.) Walp.) Genotypes for Enhanced N₂ Fixation and Water Use Efficiency under Field Conditions in Ghana. American Journal of Plant Sciences, 10, 640-658. doi: 10.4236/ajps.2019.104047.