Abstract

This dissertation focuses on the tetraploid core collection (TCC) of wheat, examining the genetic, environmental, and microbial factors that influence root and shoot traits, thereby informing breeding strategies for enhancing resilience and yield. A genetic diversity analysis of the Global Durum Genomic Resource of tetraploid wheat (Triticum turgidum ssp) accessions utilizing a 90k SNP array identified clearly distinct genetic clusters shaped by geographic origins and breeding programs. Within this collection, Triticum turgidum landraces (TDL) exhibited higher genetic diversity and localized adaptations, especially in root growth angle (RGA), a trait with high heritability impacted by population structure. Genome-wide association studies (GWAS) and haplotype analyses pinpointed significant QTL associated with RGA on chromosomes 2A, 6A, and 7A, suggesting adaptive haplotypes that could enhance extensive lateral root systems. The second part of the thesis investigated root development in TCC of 45 genotypes. Microbial treatments (unpublished) with Bacillus ssp. s50, Enterobacter ssp, and Pseudomonas syringae GR12-2. Results revealed genotype-specific responses affecting root stability and elongation: Bacillus reduced root length across genotypes with a few noticeable exceptions, whereas Enterobacter and GR12-2 promoted moderate root elongation in more genotypes, potentially linked to stress resilience. Broad-sense heritability estimates confirmed substantial genetic variation in root trait response, with some genotypes, including the durum cultivar KOFA (a Desert Durum) identified as genotypes for breeding robust root systems under varying conditions. The final part of the thesis evaluated key agronomic traits—spike length, fertile spikelet counts per spike, grain area, and thousand-grain weight (TGW)—across two years of field trials. Analysis demonstrated stable expression in traits such as spike length and seed area, both of which are polygenic. Heritability estimates revealed significant genetic contributions to variability in TGW and grain area, highlighting the potential for breeding high-yield genotypes capable of adapting to diverse environmental challenges.