Magwaza, Lembe Samukelo.Odindo, Adeyemi Oladado.Liwani, Unathi.2020-01-082020-01-0820172017https://researchspace.ukzn.ac.za/handle/10413/16723Master of Science in Crop Science. University of KwaZulu-Natal, Pietermaritzburg, 2017.Wheat is one of the most important crops grown in South Africa. However, its production is threatened by the current drought periods the country has been experiencing. This includes a decline in the production of irrigated wheat which boosted the country’s wheat production. In South Africa information which could guide irrigated wheat farmers in using less water at water stress tolerant growth stages is still in its infancy. In order to assist these farmers, the International Maize and Wheat Improvement Centre (CIMMYT) bred genotypes reported to withstand very hot and dry conditions. In contribution, this study was undertaken with the following objectives: 1) to select water stress tolerant irrigated genotypes through evaluating the response of their physiological traits after water stress at tillering, flowering and grain filling 2) to determine the growth stage at which limited water supply would have minimal effect on the growth, development and yield of eight newly developed wheat genotypes. An 8 (genotypes) × 2 (water treatments (stress and no stress (control)) × 3 (growth stages (tillering, flowering and grain filling)) factorial experiment was conducted in a randomized complete block design and replicated three times. Results for the first objective indicated that the rate of photosynthesis was only affected (p < 0.05) for genotype LM98 after water stress at tillering and LM43 after water stress at flowering. The rest of the genotypes showed tolerance (p > 0.05) in these growth stages and at grain filling. Water stress in the three growth stages did not affect (p > 0.05) the transpiration rate and stomatal conductance. Only the instantaneous water use efficiency of genotype LM43 and LM35 was not affected (p > 0.05) by water stress at tillering but affected (p < 0.05) for the same genotypes at flowering. Whereas, water stress at grain filling affected (p < 0.05) the instantaneous water use efficiency of genotype LM35, LM79, LM57 and LM98. Water stress imposed at grain filling had no effect (p > 0.05) on the relative water content. It, however, had an impact (p < 0.05) on the relative water content of LM43 and LM35 when it was imposed at tillering. The genotypes also showed susceptibility (p < 0.05) to water stress at the flowering stage with genotype LM98, LM79, LM83 and LM57 affected. It was then recommended that genotype LM35, LM79, LM57 and LM98 maintained a higher water use efficiency after water stress at grain filling. While the instantaneous water use efficiency of LM43 and LM35 was higher after water stress at tillering but reduced by water stress at flowering stage. From the results of the second objective it was discovered that the plant height of the studied genotypes was not affected (p > 0.05) by water stress at tillering and grain filling. The number of fertile tillers was reduced (p < 0.05) by water stress at tillering in susceptible genotypes while at flowering and grain filling the number of fertile tillers for all the genotypes was not affected (p > 0.05). The spike length was affected (p < 0.05) by water stress at all growth stages while the harvest index was not affected (p > 0.05). Aboveground biomass was only affected (p < 0.05) at tillering stage. Grain yield production which was the primary concern declined only after water stress at tillering. Grain yield production was more linked to the number of fertile tillers after water stress at each growth stage. Based on overall findings this study was able to recommend that the studied genotypes can be subjected to water stress at grain filling and flowering. At tillering, genotype LM83 is better at tolerating water stress while genotype LM47, LM79 and LM66 are susceptible.enWater stress.Genotypes.Growth stages.Physiological traits.Wheat.Thesis