TITLE:
Screening Cowpea (Vigna unguiculata (L.) Walp.) Genotypes for Enhanced N2 Fixation and Water Use Efficiency under Field Conditions in Ghana
AUTHORS:
Damba Yahaya, Nicholas Denwar, Mustapha Mohammed, Matthew W. Blair
KEYWORDS:
Drought, Cowpea, Carbon Isotope Discrimination, Nitrogen Fixation, Grain Yield
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.10 No.4,
April
26,
2019
ABSTRACT: 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.