الفهرس 
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Abstract
Bread wheat (Triticum aestivum L.) is one of the mostly grown crop and essential cereal crops worldwide, which used by more than one-third of its population as a staple food and contributes more calories and proteins to the world diet than any other cereal crops. Stem rust caused by Puccinia graminis f. sp. tritici, is the most destructive disease to wheat. Under favorable conditions, stem rust may cause yield losses up to 100 % to the susceptible varieties. The new stem rust race which was designated as Ug99 in Uganda in 1999 has threatened wheat production globally. 13 races belonging to the Ug99 lineage are now known in 13 countries. In Egypt three races in the Ug99 race group; TTKST, TTKTK and TTKSK were detected. The present study conducted to screening of resistance sources to stem rust Ug99 (TTKSK) in sixty wheat genotypes delivered to Egypt by International Maize and Wheat Improvement Center (CIMMYT) during 2017/2018 and 2018/2019 growing seasons under field conditions. The results revealed that Sources with Sr24, Sr26, a combination genes (Sr2+ Sr24+Sr26) and adult plant resistance genes (APR) exhibited high level of slow rusting resistance and the most effective to the prevalent Ug99 race. While, Sources with the Sr25 gene showed disease severity ranged from moderate resistant-moderately susceptible (MRMS) to susceptible (S). Sources with Sr13, Sr22, Sr42, and SrHuw234 displayed MRMS to MSS. On the other hand, sources that carry unknown genes were susceptible (S) to stem rust Ug99 (TTKSK) at the adult plant stage in both seasons. Which suggests that they confer partial or acceptable resistance to Ug99 race. from this study the slow rusting lines achieved with combining non-race specific and race specific genes that is more durable at adult plant resistance, so can used in wheat breeding programmed for stem rust resistance.
Additionally, 32 Egyptian wheat cultivars were evaluated for the level of slow rusting resistance to stem rust. Four parameters are used as a criteria to identify slow rusting in the field included average coefficient of infection (ACI), area under disease progress curve (AUDPC), relative area under disease progress curve (rAUDPC) and relative resistance index (RRI) . In all, two wheat genotypes; Sakha 93 and Sakha 94 possess race-specific resistance, 19 genotypes with different levels of slow rusting resistant and the rest susceptible genotypes were included in two experiments with and without fungicide protection under high disease stress. Our results showed the highest significant value of mean 1000 kernels weight (TKW) reduction and mean test weight (TW) reduction with susceptible genotypes were 21 and 22 %, respectively. Correlation coefficient of mean TKW and TW reduction with disease parameters; ACI, AUDPC, rAUDPC and RRI were highly significant. The slow rusting genotypes showed a range of severity response indicating phenotypic diversity, which could be used for breeding wheat genotypes in wheat improvement programs.