Plant water relations and proline accumulation on two cowpea (Vigna unguiculata (L.) Walp.) cultivars as a response to water stress
Cowpeas produced under rainfed conditions of arid and semiarid areas of Sub-Saharan Africa often experience periods of water stress. It is therefore important to identify drought tolerant cultivars of cowpeas and the mechanisms involved in their ability to withstand these conditions. The aim of this study was to evaluate the responses of physiological parameters such as leaf water potential, leaf diffusive resistance, relative water content, leaf proline content and cell membrane stability to water stress and to identify the parameters, which can be used to distinguish between drought tolerant and drought susceptible cowpea cultivars. Water stress was applied from 16 to 30 days after emergence (DAE) to two cowpea cultivar namely Akkerbone Bechuana Wit (AB Wit) and Akkerbone CH14 (ACH14) by withholding water to the stressed plants. Well-watered plants were watered regularly to keep the soil moisture content close to or at field water capacity. Water stress increased leaf diffusive resistance (LDR) and proline accumulation and decreased relative water content (RWC) in both cultivars and water potential only in AB Wit. Increases in proline content seemed to correlate more closely to changes in relative water content than changes in water potential. Water potential, relative water content and proline accumulation, therefore, seemed to be useful parameters to distinguish between drought tolerant and drought susceptible cowpea cultivars.