Analytical Study of the Research Gap in Drought Stress Physiology of Cowpea Genotypes from North East Nigeria

Cowpea improvement programmes for the drought-stressed Sahelian zone have generated improved varieties, but the specific physiological mechanisms underlying drought tolerance variation among locally collected North East Nigerian landraces have received insufficient characterisation, creating gaps in breeding programme target trait definition. This study examined the research gap in drought stress physiology of cowpea genotypes from North East Nigeria through systematic literature review and original physiological characterisation of ten landraces collected from Borno and Yobe States. A combined scoping review and empirical characterisation methodology was employed. Scoping review of 11 databases identified 67 publications from 2019 to 2024 on cowpea drought tolerance, of which only 9 specifically characterised North East Nigerian germplasm. Of these nine, none investigated membrane stability, osmotic adjustment, and antioxidant enzyme activities simultaneously. Ten landraces were subjected to progressive drought stress at the flowering stage in a screen house at the University of Maiduguri, with polyethylene glycol-induced water deficit applied. Relative water content, leaf water potential, membrane stability index, proline accumulation, and superoxide dismutase activity were measured at field capacity and at 50 and 75 percent water deficit. Results showed significant genotypic variation in all parameters. Landrace BW-07 from Borno combined the highest membrane stability (78.4 percent), lowest proline accumulation to osmotic adjustment ratio, and best relative water content maintenance, suggesting constitutive drought tolerance mechanisms. The study identifies four under-characterised physiological traits as research priorities and recommends BW-07 as a parental line for breeding programmes.

Keywords: cowpea drought tolerance, physiological characterisation, North East Nigeria, landrace germplasm, drought stress physiology