GENETIC EXPLORATION OF WHEAT D-GENOME FOR IMPROVED NUTRITIONAL AND AGRONOMIC TRAITS

OLUFUNKE MERCY AYEGBIDUN

Bread wheat (Triticum aestivum L.) is one of the world's most important cereal crops, providing a major source of calories and protein for the global population. However, genetic diversity within the D subgenome of modern wheat has been substantially reduced through domestication and breeding, limiting opportunities for continued genetic improvement. This dissertation investigated the potential of wild-derived alleles from the D-genome progenitor, Aegilops tauschii, to improve agronomic performance, grain nutritional quality, and breeding efficiency using the D-Genome Nested Association Mapping (DNAM) population.Chapter Two examined the genetic basis of five agronomic and end-use quality traits, including grain yield, plant height, heading date, test weight, and grain hardness, across multiple environments using genome-wide association analysis. Several stable marker–trait associations were identified, including a region on chromosome 7D associated with plant height, heading date, and grain yield located near an ATP-binding cassette (ABC) transporter gene. Additional loci associated with plant height were also detected outside the well-characterized Rht regions, suggesting alternative sources of genetic variation for modifying plant architecture. Chapter Three focused on the genetic architecture of grain micronutrient concentration and protein content. Genome-wide association analyses identified stable loci for iron, zinc, calcium, copper, manganese, and protein across environments. A consistent locus associated with grain iron concentration was detected on chromosome 3D near a homocysteine S-methyltransferase gene, while additional genomic regions on chromosomes 1D and 3D were associated with multiple nutritional traits. Chapter Four evaluated genomic selection strategies for accelerating the improvement of grain iron and zinc concentration. Prediction accuracy increased with training population size before reaching a plateau at approximately 60–70% of the available population. Multi-trait genomic prediction improved the prediction of iron and zinc when correlated secondary traits were available for the testing population, whereas the inclusion of weakly or negatively correlated agronomic traits reduced predictive ability. In summary, these studies show that Aegilops tauschii-derived diversity provides valuable genetic variation for improving both agronomic and nutritional traits in bread wheat. The identification of stable genomic regions associated with important traits and the evaluation of genomic prediction strategies provide useful resources for incorporating wild alleles into wheat breeding programs aimed at improving yield and nutritional quality.

GENETIC EXPLORATION OF WHEAT D-GENOME FOR IMPROVED NUTRITIONAL AND AGRONOMIC TRAITS

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