Labuschagne, Maryke T.Herselman, Liezelvan Biljon, AngelineNida, HabteEngida, Chalachew Endalamaw2024-05-212024-05-212023http://hdl.handle.net/11660/12526Thesis (Ph.D. (Plant Breeding))--University of the Free State, 2023Climate-resilient and high-yielding sorghum cultivars must be developed for sustainable food systems and improved livelihoods in sub-Saharan Africa. Low grain protein, Fe and Zn concentrations are a frequent problem in food crops and they affect the crop's nutritional value, particularly in cereals. In this study, a total of 361 Ethiopian sorghum landraces with four commercial checks were grown under well-watered, wet intermediate and natural drought conditions for two consecutive seasons. The purpose of this research was to assess the genetic diversity and drought tolerance of this Ethiopian sorghum landrace collection using agronomic and grain quality traits and to select promising lines for production and/or breeding. The specific objectives were to (i) assess the level and pattern of genetic variation and drought adaptation in a sorghum landrace collection using phenotypic traits, (ii) evaluate chemical composition, genotype by environment interaction, drought effects and environmental influence and determine performance and stability of sorghum landraces, (iii) identify genomic regions associated with grain quality to determine the genetic basis for starch, protein and mineral concentrations of Ethiopian sorghum landraces. In stress environments, yield and yield components as well as grain quality traits had low means, range, genetic variance (σ²g) and heritability values. In terms of grain yield performance under different water regimes, Melkassa (irrigated) had a 54.5% higher mean grain yield than Miesso (drought stress) in 2020 and Melkassa (irrigated) had a 26.9% higher mean grain yield than Miesso (drought stress) in 2021. Therefor drought stress reduced mean grain yield by 44.6% and grain weight by 14%. In all environments, ten genotypes (G189, G210, G125, G324, G325, G353, G319, G219, G187 and G229) had the highest stress tolerance index (STI), geometric mean productivity (GMP), mean productivity (MP) and yield in non-stress conditions (Yp) and stress conditions (Ys). In stress environments, starch content decreased by 5%, while protein content increased by 21% when compared to wet intermediate conditions. The Zn content was 60% and 55% higher in wet intermediate environments than in irrigated and stress environments, respectively. The Fe content was 21% and 13% higher in wet intermediate environments than in irrigated and stress environments, respectively. A genome-wide association study (GWAS) on 365 diverse Ethiopian sorghum landraces identified 209,572 single nucleotide polymorphisms (SNPs) (HB 𝘱 ≤ 0.05). Several candidate genes were identified that were significantly associated with grain Zn, Fe, starch, protein and ash concentrations, such as LEA, CHI, bZIP, ARF12 and WOX6. The Late Embryogenesis Abundant (LEA) and basic leucine zipper (bZIP) family of proteins are involved in various stress responses in plants. The ABC transporter and sugar carrier proteins, Auxin Response Factors 12 (ARF12), Alpha-glucan phosphorylase and Zinc finger CCHC gene, are known for starch synthesis and storage in growing seeds. The WUSCHEL-related homeobox 6 (WOX6) and TatD family of hydrolases genes, acts as a transcription factor and is known to regulate stem cell maintenance and differentiation. Chitinase (CHI), flavonoid glycosides, architecture1 (tga1) and Class III peroxidase 70 and 69 precursors are all engaged in biological processes including plant defence against pathogens. The Zinc finger proteins (ZNFs) family is involved in Zn and Fe ion uptake and transport. These genes are involved in various biological processes such as stress response, starch synthesis, plant development and defence. The identification of loci associated with grain quality provides new insight into the genetic control of the traits, while sorghum landraces with nutritious grains can serve as sources of genes for breeding for good nutritional value.encandidate genesenvironmentgrain qualitygrain yieldGWASsorghum landracesstress toleranceThesisUniversity of the Free State