Effects of water stress on the growth and yield of six accessions of cowpea (vigna uunguiculata (l) walp) from three agro-ecological zones in Ghana.

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Cowpea (Vigna unguiculata) usuallyis found to grows in the tropical and sub-tropical ecological regions of the world. It is cultivated by peasant farmers for both domestic and economic purposes. Edaphic and climatic factors affect the growth and fruit production of the crop. The Rrecent erratic rainfall in the tropics, as a result ofdue to climate change, is causing a lot of harm to affects farmers as a result of poor fruit yields of the crop. The study was to assessed the effects of water stresses on the growth and fruit yield of six accessions of cowpea from three agro-ecological zones in Ghana. The cowpea seeds of six accessions of cowpea from three agro-ecological zones were acquired from the Plant Genetic Resources Research Center (PGRRC, Bunso) and and given the experimental codes; (SD1, SD2) for those from the Semi-deciduous zone, (CS1, CS2) for the Coastal savanna and (SS1, SS2) for the Sudan savanna.. After The seeds were tested for viability tests, in the laboratory. sSixty seeds of each accession were selected planted in a ba lackblack polythene containing 2.0 Kg of well mixed soil. Twenty plants of each of the accessions were grouped under three watering regimes; W0 (for normal irrigation or control), W1 (50% water deficit) and W2 (80% water deficit), after three weeks of growth. The sample size was 360 plants. The watering was given the description W0 for the normal irrigation or control, W1 for medium water stress (50% water deficit) and W2 for severe water stress (80% water deficit). The accessions in each of the treatment protocols were sampled three times during their growth period after the start of the water stress application. Some morphological and anatomical features were measured. in-situ while tissues of the plants were processed into temporal and permanent slides for anatomical measurements under the microscope. The onset of flowering and fruiting were noted whileand the massweight of yields was measured.weighed. Environmental parameters were assessed by using appropriate instruments. The results weredata was subjected to analysis using of variance (ANOVA ) by the Microsoft Excel software, and the means separated by using the least significant difference at P<=0.05. The results show that Aall the accessions exhibited a general reduction in the size of their morphological, and anatomical features and fruit yields as under severity in the water stress increasedapplications, an exception was found in the frequency of xylem vessels and the cutin cover on the leaves which increased along the stress treatments. Plasmolysis in the cells may have caused the cell reductions while the plants may have increased the production of xylem vessels with smaller lumen to tolerate the water deficit condition. The accessions from the Semi-deciduous (SD1, SD2) zone performed well under the normal watering but showed widerthe highest significant reductions in featuressizes and fruit yields along theincreasing water stress regimes. The accessions from the Coastal savanna (CS1, CS2) showed the lowest reductions in both their morphology and anatomy along the water stressed regimes, and also produced the largest amount of fruits in the stressed regimes. The accession CS1 was inferred to be the most appropriate accession for cultivation in the dry ecological regions of Ghana.
A thesis submitted to the Department of Theoretical and Applied Biology, Kwame Nkrumah University of Science and Technology in fulfilment of the requirement for the award of the degree of Master of Philosophy in Biological Sciences