Shimelis, Hussein Ali.Odindo, Alfred Oduor.Tshikunde, Nkhathutsheleni Maureen.2020-03-252020-03-2520192019https://researchspace.ukzn.ac.za/handle/10413/17033Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.Drought stress is one of the most important limiting factors to sustainable and profitable wheat production in sub-Saharan Africa (SSA), including South Africa. Use of drought adapted genetic resources is regarded to be the most economic and environmentally friendly approach to mitigating the adverse effects of heat and drought stress. Therefore, there is need to select desirable wheat genotypes with enhanced water-use efficiency and drought tolerance parameters to boost wheat production in water-limited environments. Genotypes with enhanced drought-tolerance and water-use efficiency can be developed targeting yield-related agronomic and physiological traits which are well-correlated with grain yield potential. Therefore, the objectives of this study were: 1) to determine drought tolerance of dryland wheat genotypes based on leaf gas exchange and water-use efficiency in order to identify promising genotypes for drought tolerance breeding and 2) to examine associations between morphological and physiological traits of selected wheat genotypes under drought stress in order to identify unique traits that may be used as direct or indirect selection criteria for improving water-use efficiency and drought tolerance in wheat. In the first study, leaf gas exchange and water use efficiency of ten genetically diverse wheat genotypes were tested under water-stressed and non-stressed conditions. Results showed high significant differences (P < 0.001) in water condition x genotypes interaction with regards to net photosynthetic rate (A), the ratio of net CO2 assimilation rate and intercellular CO2 concentration (A/Ci), the ratio of intercellular and atmospheric CO2 (Ci/Ca), intrinsic water-use efficiency (WUEi), instantaneous water-use efficiency (WUEinst) and water-use efficiency (WUE). This suggests that genotypic variability of wheat exists for these traits. Heat and drought tolerant wheat genotypes such as G339 and G334 were identified and selected for breeding for enhanced drought tolerance possessing suitable physiological traits such as high A, transpiration rate (T), stomatal conductance (gs), A/Ci, WUEi and WUEinst under drought stress condition. In the second study, response of wheat genotypes were assessed based on morpho-physiological traits and water use efficiency under water-stressed and non-stressed conditions. Significant differences (P< 0.05) were observed among the tested wheat genotypes with regards to the number of productive tillers (NT), number of leaves per plant (NL), total dry mass (DM), leaf area index (LA), leaf area ratio (LAR), A, gs, T, WUEinst, WUEi, WUE. Pearson’s correlation analysis indicated that NL, NT, plant height (PH), DM, grain yield (GY), A were positively and significantly correlated with WUEinst. Instantaneous water use-efficiency positively correlated with NL (r = 0.76; P < 0.001), NT (r = 0.67; P = 0.03), PH (r = 0.72; P = 0.01), DM (r = 0. 81; P < 0.001) and GY (r = 0.70; P = 0.02) under water stress (WS) condition. Wheat genotypes namely: G339, G343 and G344 which exhibited high NT and DM under WS condition were selected with enhanced water-use efficiency. Overall, the present study evaluated and selected drought tolerance wheat genotypes that can be used to improve wheat grain yield under water stress conditions. Furthermore, morphological traits (NT and DM) and physiological traits (A, T, gs, A/Ci and WUE) well-associated with water-use efficiency were detected. These traits can be used as direct and indirect selection criteria in dry land wheat improvement programmes.enPhysiological traits.Effect of genotype.Soil moisture content.Thesis