College of Agriculture

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The College of Agriculture is committed to advancing agricultural education, research, and community service. It serves as a center for knowledge creation and dissemination in crop science, animal production, natural resource management, and sustainable agriculture.

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Subject: search.filters.subject.Genetic diversity

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    GENETIC DIVERSITY AND GENOME-WIDE ASSOCIATION MAPPING IN TETRAPLOID WHEAT (TRITICUM TURGIDUM SPP.) GERMPLASM OF ETHIOPIA
    (Hawassa University College of Agriculture, 2024) MIHERETU FUFA GELETA
    Genetic Diversity and Genome-Wide Association Mapping in Tetraploid Wheat (Triticum turgidum spp.) Germplasm of Ethiopia PhD Dissertation Miheretu Fufa Geleta Hawassa University, 2024 Ethiopia is a center of diversity for Tetraploid wheat (Triticum turgidum spp.) species, which hold ample genetic variation; howevr, the country remains a net importer of wheat due to a huge gap between production and consumption. The present study was aimed to investigate the extent and pattern of diversity based on phenotypic traits, grain quality traits, and molecular markers; and Genome-Wide association studies for phenotypic and grain quality traits. Diversity assessment at the entire genotypes based on the qualitative traits revealed intermediate (0.60±0.01) diversity and high diversity concerning glum color (0.78), spike density (0.61), and seed color (0.86); however, low diversity for awndness (0.15). All qualitative traits showed highly significant (p<0.001) variation across regions of collections and altitudinal classes; however, only spike density was significantly (p<0.05) different at the species level. Within populations diversity was higher than between population diversity. Analysis of variance based on the quantitative traits revealed highly significant variation (p<0.001) among genotypes and for genotype by location interaction in all traits except for the number of effective tillers per plant. The observed mean and range values of the phenotypic traits revealed high variability in the accessions. Phenotypic Coefficient of Variation (PCV) and Genotypic Coefficient of Variation (GCV) values were high for grain yield, biomass yield, and harvest index. The estimates of heritability (H2 ) ranged from 41.78 to 84.62 % respectively for grain yield and the number of seeds per spikelet. High genetic advance as a percentage of mean was observed for the number of seeds per spikelet, the number of effective tillers per plant, grain yield, biomass yield, and harvest index. The number of seeds per spikelet gave a high value of genetic advance and heritability implying high genetic gain from its selection. Grain yield showed a highly significant (p<0.001) negative correlation with days to booting and days to maturity and a positive correlation with the remaining quantitative traits. The combined ANOVA based on the grain quality traits revealed a highly significant variation (p < 0.001) among the genotypes and for genotype by location interaction for all traits. The genotypes showed a wide range in their thousand kernel weight, zeleny index, and vitreousness percentage. Grain yield and protein content, respectively, showed high and low values of PCV and GCV; however, an intermediate value of PCV and GCV was observed for gluten content and thousand kernel weight. Zeleny index and vitreousness percentage showed high PCV and intermediate GCV; however, protein content showed low PCV and GCV. The estimate of broad sense heritability (H2 ) ranged from 33.57 % for vitreousness percentage to 66.36 % for zeleny index. The values of genetic advance and GAM observed were respectively high for grain yield (31.94, 26.91) and zeleny index (31.89, 29.34); intermediate for thousand kernel weight (18.27, 16.59), gluten content (15.70, 13.55), and vitreousness percentage (15.75, 12.97) and low for protein content (9.81, 8.44). Grain yield showed a highly significant positive correlation with thousand kernel weight (0.43***) and vitreousness percentage (0.19**) and positive correlation, but not significant, with protein content, gluten content, and zeleny index. xxi Principal component analysis (PCA) based on phenotypic traits showed that the first and second principal components (PC) respectively accounted for 19.74% and 15.96 of the total variation in the entire genotypes, respectively. The first five principal components combined explained 61.21 % based on the entire genotypes. On the other hand, PCA of grain quality traits showed that the first and second PCs respectively accounted for 34.12 % and 20.65% of the total variation and the three PCs explained 69.11% of the total variation in the entire genotypes. Eleven landraces and eleven improved varieties were top performing based on their grain yield and grain quality traits. Clustering based on phenotypic traits and grain quality traits respectively grouped the whole genotypes into seven and six clusters without clear regional grouping. Furthermore, the genetic diversity and population structure were investigated for the study panel as well as the landraces based on 10349 DArTSeq markers distributed across A and B genomes. The study panel was clustered into two populations: pop1 and pop2 respectively comprising 150 landraces and 3 released varieties and 19 released varieties and 12 landraces pop2 being more diverse than pop1; likewise, landraces were clustered into two subgroups. Analysis of molecular variance (AMOVA) revealed highly significant (P<0.001) variation between populations and within populations the latter being higher than the former implying that more attention should be given to individual accessions within populations to explore the existing genetic diversity. Little to moderate genetic differentiation (Fst) was respectively reported for the landraces (0.028) and the study panel (0.117) implying no significant differentiation among populations. High gene flow (1.297-8.818) was recorded based on DArTSeq markers at all level. PCA based on DArTSeq markers grouped the released varieties and the landraces separately in the study panel; however, PCA of the landraces did not show clear groupings. 127 genotypes were reported to have one or more private alleles at 755 loci, an indication of key adaptive genes at these loci to be exploited in breeding programs. In conclusion, high genetic diversity was detected in Ethiopian tetraploid wheat germplasm, which could be utilized for future wheat breeding programs. The landraces ETW115 and ETW135 and the released varieties (Tesfaye and Bekelcha) could be used in a crossing program owing to their maximum genetic distance. Analysis of genome-wide LD in the whole collection showed that 44.98% of the total marker pairs had a significant LD (p<0.01) with a mean r2 value of 0.129791. 44.59% (18668) and 8.62% (3609) of the significant marker pairs showed r2 values above 0.2 and 0.7, respectively, indicating a higher level of LD in the genome. The number of significant marker pairs observed was higher in the B genome (24.44%) than the A genome (20.54%). GWAS identified 44 SNPs, two of which are pleiotropic, across chromosome 1A, 2A, 2B, 3A, 3B, 4B, 5A, 5B, 6A, 6B, and 7B that were significantly (FDR <0.05) associated with some of the traits studied. Thirty-five QTLs were reported while the remaining 9 QTLs were found to be novel, which need to be validated for further use in the breeding program. We also identified several candidate genes, potentially regulating the traits, and encoding various proteins involved in plant growth and development. Hence, this study highlights the significance of the Ethiopian tetraploid wheat gene pool for improving tetraploid wheat globally; thus, a breeding strategy focusing on accumulating favorable alleles at these loci could improve tetraploid wheat production in Ethiopia and beyond
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    GENETIC DIVERSITY AND DROUGHT TOLERANCE IN ETHIOPIAN DURUM WHEAT (Triticum turgidum subsp. durum) GENOTYPES
    (Hawassa University College of Agriculture, 2025) BANTEWALU HAILEKIDAN DUKAMO
    Durum wheat (Triticum turgidum subsp. durum), the second most widely cultivated wheat species after common wheat, plays a crucial role in global food security. Ethiopia, recognized as a secondary center of origin and diversity for durum wheat, harbors a broad and unique genetic reservoir well adapted to diverse agroecological conditions. However, productivity remains low due to limited availability of improved, drought-tolerant varieties and insufficient exploitation of genetic diversity. This study aimed to characterize Ethiopian durum wheat landraces, identify drought-tolerant genotypes, and assess their potential for breeding programs by integrating field, greenhouse, and molecular analyses. The research involved three interlinked components. The first was a field experiment conducted at Dera (1500 masl) and Debrezeit (1920 masl), where 104 genotypes (100 landraces and 4 checks) were evaluated under drought-stressed and non-stressed conditions using an augmented design. Thirteen agronomic traits related to yield, phenology, and canopy status were measured across both environments. Additional data were collected from an extended growing season, and drought tolerance was assessed using various indices. ANOVA, correlation, principal component analysis (PCA), and clustering were used to identify promising genotypes and trait associations. The second component involved a greenhouse experiment at Hawassa University using 20 top-performing landraces and four checks selected from the field study. Genotypes were grown under well-watered (70% field capacity) and drought-stressed (35% field capacity) conditions in a completely randomized design with three replications. Data on morphological, physiological, and biochemical traits were collected, including grain yield, relative leaf water content (RLWC), chlorophyll content, canopy temperature, and proline accumulation. Statistical analyses were employed to evaluate drought responses, including correlation, PCA, cluster, and path coefficient analysis. The third component focused on the molecular characterization of 94 genotypes (86 landraces and 8 improved varieties) using SNP markers generated through DArTSeq technology. Genotyping was performed by SEQART AFRICA, producing 17,092 highquality SNPs. Genetic diversity, population structure, and linkage disequilibrium (LD) were analyzed to assess genome-wide variation and support genotype selection. Field results revealed significant genetic variation among landraces across all measured traits. Genotypes ETDW/15DZ23, 34493, ETDW/15DZ4, 34522, MCD3-14, 34217, and 31831 demonstrated superior grain yield under stress and non-stressed conditions. High heritability (h²b = 32.84–97.87) and genetic advance estimates for traits such as spike length, kernel number per spike, and tiller number indicated strong potential for selection. Drought indices, including stress tolerance index (STI), mean productivity (MP), and yield stability index (YSI), identified ETDW/15DZ23, 34493, and ETDW/15DZ4 as topperforming, drought-resilient genotypes. Strong positive correlations (r = 0.88) between grain yields under stressed and non-stressed conditions further confirmed their stability and xviii adaptability. The greenhouse experiment revealed significant effects of genotype, treatment, and their interaction (P<0.001) for most traits. Under stress, grain yield decreased by up to 68%, RLWC dropped from 93.07% to 44.91%, and proline content increased markedly, indicating drought response. Cluster analysis grouped genotypes based on resilience, with one cluster showing the highest yield (5.99 t/ha) under well-watered conditions, while another showed superior RLWC (65.80%) and yield (2.90 t/ha) under stress. Path analysis underscored the importance of RLWC, proline, and chlorophyll content in drought tolerance. Molecular analysis revealed 14,136 informative SNPs distributed across the A and B genomes, with chromosome 2B having the highest marker density. Population structure analysis indicated considerable variation within and among landraces, with AMOVA showing 51.75% of genetic variation within populations and 48.15% within individuals. The genome-wide LD decay threshold was 4.58 Mbp, with the highest LD values on chromosome 4B. Average polymorphic information content (PIC) and gene diversity values were moderate, indicating a diverse and informative marker set for future breeding applications. This study highlights the significant phenotypic and genotypic diversity within Ethiopian durum wheat and identifies promising genotypes for drought tolerance and yield stability. The integration of field performance, physiological traits, and genomic data provides a robust platform for developing improved durum wheat cultivars. These findings support the use of landraces in breeding programs targeting climate resilience and food security. Future work should focus on multi-environment trials, genome-wide association studies (GWAS), and marker-assisted selection to accelerate genetic improvement and enhance drought tolerance in Ethiopian durum wheat