الفهرس 
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Abstract
Two sets of filed experiments were performed at the Experimental Stations of Agriculture Rresearch Center, Egypt during the three successive growing seasons 2015/2016, 2016/2017 and 2017/2018. The first set of experiments included twelve bread wheat genotypes were grown to evaluate grain yield, its contributing characters and yellow rust resistance in two Agriculture Research Stations representing different governorates in Egypt i.e Kafer El-Hamam (Sharkia) and Sakha (Kafer El-sheikh) belonged to the Agriculture Research Center, Egypt, during 2015/2016 and 2016/2017 winter successive growing seasons at two sowing dates (20 Nov and 15 Dec). The second set of experiments included eight parental wheat genotypes to introduce six crosses. The six populations i.e., P1, P2, F1, F2, BC1 and BC2 of the six wheat crosses were grown at Kafer El Hamam Station during the three growing seasons 2015/2016, 2016/2017 and 2017/2018 under artificial infection with physiological races of yellow rust. The obtained results displayed significant differences among the tested locations, sowing dates, and genotypes for most measured traits. The yellow rust measurements viz, final rust severity (FRS), the average coefficient of infection (ACI), and area under disease progress curve (AUDPC) revealed that Giza-171, Misr-1, Gemmeiza-12, Shandweel-1, Sids-13, Line-1, Line-2, and Line-55 had better resistance. Based on heat sensitivity measurements, Line 1 and Line 2 followed by Line 35, Shandweel-1 and Line-55 were classified as more tolerant to heat stress compared with the remaining genotypes. The genotypes Line-55, Gemmeiza12, Giza-171, Line-1, Line-2, and Misr-1 were able to maintain acceptable agronomic performance under timely and late sowing dates in all evaluated environments. Different statistical procedures were employed to explore the adaptability and stability of tested genotypes i.e., joint regression, stratified ranking, Wricke’s Ecovalence values, cultivar superiority, additive main effects, and multiplicative interaction (AMMI), AMMI stability value, and genotype plus genotype-by-environment interaction (GGE). The applied stability parameters were quite similar for describing the stability of the evaluated wheat genotypes. Gemmeiza-12, Giza-171, Sids-12, Shandweel-1, Line-1 and Line-2, were desirable and stable. The heatmap and hierarchical clustering were exploited for dividing the evaluated bread wheat genotypes into different clusters based on yellow rust resistance measurements, heat tolerance indices, and agronomic performance. Line-1 and Line-2 had the best performance for all rust resistance, heat tolerance, and agronomic performance followed by Giza-171, Line-55, Line-35, Gemmeiza-12, Shandweel-1, Misr-1, and Sids-13. In conclusion, our findings provide evidence of utilizing promising genotypes in rust resistance, heat tolerance, and agronomic performance in breeding programs for improving wheat grain yield stability mainly under climate change. Results of second experiment, six bread wheat populations (P1, P2, F1, F2, BC1 and BC2), revealed highly significant differences due to genotypes, parents and their cross populations for all studied characters. The first Gemmeiza 12 × Sids 13 and second Gemmeiza 12 × Line 55 crosses were more resistant to yellow rust. A clear heterosis strength appeared in most of the crosses understudy. Narrow sense heritability “Tn” was high (>50%) for number of spikes per plant, number of grains per spike, spike grain weight and final rust severity as well as relatively moderate for grain yield per plant.