Browsing Doctoral Degrees (Genetics) by browse.metadata.advisor "Agenbag, G. A."
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- ItemDrought tolerance studies in spring wheat cultivars produced in South Africa(Stellenbosch : Stellenbosch University, 1999-12) Strauss, Johannes Abraham; Agenbag, G. A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics & Institute of Plant Biotechnology.ENGLISH SUMMARY: Drought is considered, worldwide, to be the most important factor limiting crop yields. Spring wheat produced in the Western Cape region of South Africa is also affected by water stress. The onset of global warming may cause periods of water stress in the winter rainfall regions of South Africa more frequently, which makes it important to identify spring wheat cultivars that can withstand these conditions. The aim of this study was to determine whether cultivar differences in drought tolerance could be detected through the use of a series of physiological tests on spring wheat plants subjected to water stress at different growth stages. Furthermore to determine whether differences in physiological responses would be of any commercial value. To evaluate this, plants were analyzed to compare biomass production, yield and quality of stressed and control (unstressed) plants. A preliminary trial showed that the withholding of water might be more appropriate in the induction of water stress than the use of polyethylene glycol. The trial also showed that the reduction of 2,3,5-triphenyltetrazoliumchloride (modified method) was not sensitive enough to detect water stress in spring wheat. The evaluation of the physiological parameters showed that differences in drought tolerance do exist in spring wheat cultivars produced in the Western Cape region. The accumulation of proline and the water content of leaves proved to be the most sensitive parameters tested. A combination of these parameters may provide valuable information in newly bred spring wheat cultivars. In a study on biomass production it was shown that the above ground biomass was reduced by applied water stress. No clear distinctions in drought tolerance could, however, be made between cultivars. The use of leaf area (rate of leaf abscission) shows promise as a method to distinguish between drought tolerant cultivars. Yield and the yield components of all cultivars tested were severely reduced by water stress at both the flag leaf-, milky kernel growth stage. Although reductions in yield and yield components was shown, no single cultivar proved more tolerant than the other. The application of water stress resulted in a general increase in kernel protein content. Flour yield was lower, due to a relatively smaller production of non-protein components in the kernel. Although protein content increased with increased water stress, no significant differences were noted in micro-loaf volumes. The results of the mixograph parameters tested were also similar.