Alaa Youssef Salah Youssef creator preparation. Mohamed Salah EL Soda thesis advisor. Neama Hussein Osman thesis advisor. Atef Abdel Fatah Mohamed Shahin thesis advisor. text theses ua 2025 monographic eng ara 138 pages : illustrations ; 25 cm. + CD. This study was conducted from 2019 to 2020 at Merchouch (Morocco) and Izmir (Turkey), and from 2022 to 2023 at Sakha and Sids (Egypt), to investigate the genetic variability of stripe rust resistance in spring bread wheat. Stripe rust, caused by Puccinia striiformis f. sp. tritici, is a major biotic stress affecting wheat (Triticum aestivum) production worldwide. Identifying resistant wheat genotypes and their associated genomic regions is crucial for breeding programs aimed at improving stripe rust resistance. In this study, a panel of 154 spring bread wheat genotypes from the International Center for Agricultural Research in the Dry Areas (ICARDA) was evaluated across the four locations. Disease severity was assessed under natural field infection at the adult plant stage using the coefficient of infection (CI) as a quantitative measure of resistance. Genomic DNA was genotyped using 17,692 high- quality single-nucleotide polymorphism (SNP) markers, and genome-wide association studies (GWAS) were performed to identify significant marker– trait associations (MTAs) related to stripe rust tolerance. The mixed linear model (MLM), accounting for population structure and relatedness, was applied to each environment. A total of 136 significant MTAs were identified (−log10 (p) > 3.0), with the strongest associations located on chromosomes 2A, 3B, 4A, 5B, and 7A. Several MTAs were found near known resistance genes, including Yr18 and Yr57, while others appeared to represent novel loci. These findings highlight the polygenic nature of stripe rust tolerance in wheat and the influence of environmental variation on tolerance expression. The results provide valuable insights into the genetic architecture of tolerance and offer potential targets for marker-assisted breeding. أُجريت هذه الدراسة خلال عامي 2019–2020 في مرشوش (المغرب) وإزمير (تركيا)، وخلال عامي 2022–2023 في سخا وسدس (مصر)، بهدف دراسة التباين الوراثي لمقاومة صدأ الأوراق المخططة في قمح الخبز الربيعي. يُعد صدأ الأوراق المخططة، المتسبِّب عن فطر Puccinia striiformis f. sp. tritici، من أهم عوامل الإجهاد الحيوي التي تؤثر في إنتاجية القمح (Triticum aestivum) عالمياً. ولذلك يُعد تحديد الطرز الوراثية المقاومة ومناطق الجينوم المرتبطة بها أمراً بالغ الأهمية لبرامج التربية الهادفة إلى تحسين مقاومة القمح لهذا المسبب المرضي.في هذه الدراسة، جرى تقييم مجموعة مكونة من 154 طرازاً وراثياً من قمح الخبز الربيعي التابعة للمركز الدولي للبحوث الزراعية في المناطق الجافة (إيكاردا) عبر المواقع الأربعة. specialized by Alaa Youssef Salah Youssef ; Supervisors Dr. Mohamed Salah EL Soda, Dr. Neama Hussein Osman, Dr. Atef Abdel Fatah Mohamed Shahin. Thesis (M.Sc)-Cairo University, 2025. Bibliography: pages 114-138. Issues also as CD. Text in English and abstract in Arabic & English. Disease ‪Wheat ‪ أمراض القمح Wheat Stripe rust GWAS Marker trait associations القمح الصدأ المخطط 633.11 EG-GICUC 260411 20260426115415.0 eng