Effect of water stress applied at different stages of growth on seed yield and water-use efficiency of Cowpea

Faculty of Agriculture, University of Khartoum, 13314 Shambat, Sudan *Cell phone: +249912988847 ABSTRACT Previous studies report conflicting results regarding the sensitivity of cowpeas (Vigna ungiculata (L.) Walp.) to growth stage water deficits. A field study was designed to monitor the effects of water deficit imposed at different growth stages on yield and water use of cowpeas and to identify any critical stages of development when cowpea is particularly sensitive to water deficits. The experiment was conducted for two consecutive seasons during 2005/06 and 2006/07, plus a pot experiment in the Demonstration Farm of the Faculty of Agriculture at Shambat, Sudan. Three contrasting cowpea genotypes were used in this study, namely; Ein el Ghazal (an introduced cultivar), Zalingei (local type) and Elobied (local type). The well-watered plants were irrigated at 10 days interval and in the stress treatments water was applied at 20 days interval during the vegetative stage (SV), the reproductive stage (SR) and both stages (CS). The results showed that, the reproductive stage of development is the most sensitive to water deficit in cowpea, causing a reduction in water-use efficiencies and seed yields of at least 50% in all three genotypes. In contrast, the genotypes showed a better ability to recover from stress at vegetative stage. The reduction in seed yield was associated with reductions in number of harvested pods per plant, number of seeds per pod and seed size. Differences between the genotypes were significant and in this regard, the introduced cultivar had better yield and higher water-use efficiency compared to the local types. This study suggests that there is considerable variation between cowpea genotypes in tolerance to water stress, and that maximizing the number of pods and seeds are among the most important traits for maintaining stable and high seed yields under water deficit conditions.