Physiological Responses of Some Drought Resistant Cowpea Genotypes (Vigna unguiculata (L.) Walp) to Water Stress
Drought is an abiotic stress that affects the growth of cowpea genotypes in Sub-saharan Africa One of the first physiological responses to water stress in crops is the functioning of the leaf. The aim of the present study is to determine leaf physiological responses of cowpea to water stress. The study was conducted at International Institute of Agriculture (IITA) Kano state, Nigeria during the period of 17th November to 23rd December 2009. Seven cowpea genotypes differing in drought resistance were evaluated. The experiment was laid out in randomized complete design with three treatment regime, which include unstressed (control), moderate and severe water stress condition. The criteria measured include, Chlorophyll fluorescence parameters, chlorophyll content (SPAD), Water Use Efficiency (WUE) specific leaf area (SLA), shoot and root biomass. The results showed that water stress significantly reduced chlorophyll content (SPAD). 100% reduction was recorded in moderate and severe water stress. The results of photochemical yield (Fv/Fm) indicated that 71% of the genotypes at severe stress had reduction in Fv/Fm, while 42% was recorded in moderate stress. Genotype IT98K-555-1 recorded the highest reduction in Fv/Fm. The result showed a positive correlation between photochemical yield and chlorophyll content (SPAD) at unstressed (r= 0.921), moderate (r=0.903) and severe (r= 0.861) at 5%. Water stress significantly reduced above ground biomass. Lower biomass was recorded more under severe water stress. Reductions in shoot biomass were more significant in IT0K-835-45 and IT98K-555-1. At severe water stress, most of the genotypes recorded lower water use efficiency, except in genotype IT00K-901-5. The results showed a general increase in root biomass in moderate and severe water stress condition, except in IT00K-835-45 and IT96D-610. Increases in the root biomass were recorded more under moderate stress.
Keywords: Water stress, Water Use Efficiency, Leaf physiology, Drought Resistance, Cowpea (Vigna unguiculata (L.) walp)