Cowpea (Vigna unguiculata L. Walp) is a widely grown leguminous crop in Ghana. This study was conducted using four varieties of cowpea based on the colour of the seed coat namely; Red, Brown, Black and Cream cowpea varieties. These cowpea varieties were subjected to three different watering regimes namely normal, moderate and severe water stress regimes. These different watering regimes were used as potential screening criteria to determine their drought tolerance ability. We monitored changes in physiological, morphological and yield traits due to the effects of four seed coat colour varieties and imposed water regimes. The effects of seed coat colour on relative water content (RWC) was significant (F = 13.15; p ≤ 0.05). Red variety recorded the highest RWC (60.14%) with the lowest RWC (50.71%) in the Black seed colour, all under severe water stress. The Red and Cream seed coats had a soil moisture content (SMC) of 62.61% and 48.70% respectively when the severe water stress treatment was considered. There was a decreasing trend in chlorophyll content for all four cowpea varieties. The Brown and Red varieties recorded the highest chlorophyll contents under moderate and severe water stress respectively. Proline concentrations were high with increasing drought severity. The Red cowpea variety recorded the maximum concentration of free proline (5.7µg/g) under severe water stress. Mean seed weight in Red seed coat, subjected to severe water stress, was 0.48 g. Results in this experiment revealed that the Red seed coat colour appeared to be tolerant to severe water stress compared to Cream, Black and Brown seed coats.

Keywords: Cowpea, seed coat colour, water stress, relative water content, soil moisture content