Effects of water stress on the leaf physiology and grain yield of some drought resistant cowpea genotypes (Vigna unguiculata (l.) (Walp)
Cowpea adapts to drought through escape, avoidance or tolerance mechanism. The aim of the present study was to screen for drought resistance through analysis of leaf physiological traits (stomatal conductance and chlorophyll content) and grain yield of cowpea subjected to different water stress conditions. Field experiments were conducted at IITA farm centre in Wasai (longitudes 8o 37o E and latitude 12o 11o N) located in Minjibir local government area of Kano State, Nigeria, during the terminal rainy season from 27th September to 3rd December 2008. The experimental material comprised of twenty cowpea lines arranged in randomized complete block design with three treatment regimes, which include wet (unstressed), moderate (pod-filling stages) and severe (vegetative stages) water stress condition. Soil moisture was monitored using Neutron Moisture Meter. Physiological traits measured include leaf stomatal conductance and chlorophyll content (SPAD) measured at 17 and 33 days after water stress induction and agronomic components. The results showed that, at 33 days after water stress induction, reduction in chlorophyll content (SPAD) was 100% under vegetative and pod-filling stages. However 99% of the genotypes respond to water stress by reducing their stomatal conductance at vegetative and pod-filling stress, variety IT00K-1217 and IT00K-898-2 had an increase in their conductance (1.22% and 2.54%). The results revealed that drought stress reduced grain yield component more at vegetative (76.25%) than at pod-filling stage (64.88%).