COMPARATIVE MORPHOLOGICAL AND PHYSIOLOGICAL RESPONSES OF THREE COWPEA (VIGNA UNGUICULATA L. WALP.) CULTIVARS TO INDUCED WATER, SALINITY AND COMBINED WATER AND SALINITY STRESSES

Cowpea (Vigna unguiculata L.) is a major leguminous grain mostly cultivated in semi-arid and arid regions. Thus, cowpea production is usually hampered by abiotic stresses such as drought and salinity. In this study, three local cowpea cultivars (Asontem, Kirkhouse, and Wangkae) were screened for their tolerance to water deficit stress, salt stress, and combined drought and salt stress. Plant growth, as measured by plant height and internode length, was negatively impacted by the applied stresses in all the cowpea varieties tested. The Asontem cultivar showed better growth characteristics under severe drought and salt stress. With respect to yield parameters, the Asontem cultivar recorded the highest mean seed number per pod under the various levels of drought and salt stress applied except under combined salt and drought stress treatment where Kirkhouse recorded the highest value for the same yield parameter (mean seed number per pod). Asontem and Kirkhouse accumulated more phenols than the Wangkae cultivar under severe drought stress. Kirkhouse recorded the highest phenolic content (7.677± 0.0150 mg GAE/ L) under 50 mM NaCl whereas the highest for Asontem (7.486 ± 0.301 mg GAE/ L) was detected under 150 mM NaCl concentration. It was concluded in this study that the cultivars used in this study responded differently to imposed drought and salinity stresses. It appears that Asontem and Wangkae exhibited the most and least tolerance, respectively, to drought, salinity and combined drought and salinity stresses.