Browsing by Author "Khambule, Mhlengi Sboniso"

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    Improving water stress tolerance of triticum aestivum by means of male sterility marker assisted recurrent selection
    (Stellenbosch : Stellenbosch University, 2022-12) Khambule, Mhlengi Sboniso; Botes, Willem; Hess, Lezaan; Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics.
    ENGLISH ABSTRACT: Wheat is the most widely grown cereal. More than 90% of the crop is grown for direct human consumption with increasing alternative potential for starch, glutens and biofuels. Wheat agronomic and genetic improvements will increasingly play key roles in meeting current and future food security needs and/or demands, particularly in the face of climate change. With the crop’s genetic complexity, the use and potential of molecular markers in the breeding process cannot be overlooked. The aim of this study was to select crossing parents for wheat vegetative water stress improvement under low water retention. The 4th Wheat Yield Consortium Yield Trial nursery (4-WYCYT) from CIMMYT was used as a prospective donor and evaluated for vegetative water stress tolerance at different vegetative growth stages before selection and crossing with an existing MS-MARS base population. The initial evaluation was undertaken in a growth chamber setting, selection trials were undertaken in in glasshouse conditions while crossing events used a combination of these environments. Seeds resulting from the crossing events were evaluated for early vegetative vigour under glasshouse conditions. Water retention and water availability regimes facilitated various stress combinations in both the evaluation and selection trials. Water availability was a strong factor under growth chamber (GC) conditions. Early vegetative water stress survival ranged from 16-30 plants and varying across the four retention regimes under growth chamber conditions. Survival was comparable under glasshouse conditions despite growth stage of water stress onset. Evaluated entry (EE) 005 (particularly accessions 005A and 005D) performed consistently in both growth chamber trials despite stage of stress onset, and when stress occurred during early vegetative stages despite growth environment. The said entry recorded the highest evaluated average entry yield for early vegetative stress (average of yield or total seed mass performance of available accessions for a given entry) although a single accession from EE - 006 recorded the highest individual yields (significant from two other accessions of the same genotype) when stress occurred during mid-vegetative growth under glasshouse (GH) conditions. All evaluated local checks (5 in GC and 10 in GH) performed significantly below the best performing accession and/or entry for yields in both the respective glasshouse trials, with an above average performance only when stress occurred later in the vegetative growth stages. Mid-vegetative stressed trials however recorded the least yields comparatively. The 4-WYCYT was however robust and displayed varying tolerances to water stress. This informed the selection of entries of this nursery which resulted to a male fertility segregating population produced through male sterility mediated introgression. Low retention evaluated F1 male fertile seedlings were taller on average compared to their infertile counterparts. Future studies should aim to improve wheat vegetative resilience and growth in varied and relevant water stress combinations.