Ten genotypes of bread wheat were crossed in a line x tester mating design. The twenty-one F1's and their parents (seven lines and three testers) were estimated under three levels of nitrogen fertilizer; low (25 kg N/fed), mid (50 kg N/fed) and normal (75 kg N/fed) in three experiments. Each experiments in a randomized complete block design with three replications at the Experimental Farm, Faculty of Agriculture, Menoufia University, Shebin El-Kom, Egypt during 2019/2020. The results cleared that nitrogen fertilizer levels mean squares were significant for all studied traits. A significant difference was found among lines, testers, line x testers and their interaction with nitrogen levels for all studied traits. Analysis of genetic revealed that GCA and SCA variances were significant for all studied traits under different levels of nitrogen fertilizer, indicating the importance of both additive and non-additive components in the inheritance of these traits. However, the hybrids L1 x T1, L2 x T1, L2 x T3, L3 x T2, L4 x T2, L5 x T2, L6 x T2, L7 x T1and L7 x T3were excellent harmonious combiners for specific combining ability effects for grain yield per plant and most of its components under different nitrogen fertilizer levels. The parental lines 1, 4, 6 and 7 proved to have better general combiners for grain yield per plant and most of its components under different levels of nitrogen. Therefore, these genotypes must be taken care of when breeding to tolerate low levels of nitrogen fertilization.

Some promising bread wheat lines (Triticum aestivum vulgare L.) generated from interspecific hybridization program at Sids Agricultural Research Station, ARC, Egypt and two standard checks cultivars (Sakha 94 and Sids 1) were evaluated for grain yield performance and its components and phenotypic and genotypic stability across ten environments represent North, Middle and South Egypt. Results of the combined analysis of variance for the traits under study showed highly significant effects for lines, environments, and line by environment interaction. The means of grain yield for individual lines ranged from 2.42 to 3.18 Kg/plot. When the phenotypic grain yields were subjected to stability analysis against an environmental index according to Eberhart and Rusell (1966), the regression coefficients for individual lines ranged from 0.51 to 1.17. Among the lines tested, lines no. 1, 2, 3, 5, 6, 9, 21 and 22 characterized-on phenotypic stability lines across all environments. Regarding the genotypic stability according to Tai (1971), with probability 90%, lines number 3 and 7 have genotypic stability for grain yield under the ten environment.

Source and sink relationship determine the growth and development in cereals, and can serve as reliable indicator to estimate durum wheat yield. A multi-year field trial was executed on ICARDA farm, Sids Agricultural Research Station farm, Agricultural Research Center (ARC), Egypt, during the two successive growing seasons of 2018/2019 and 2019/2020 to determine the effect of defoliation (source and sink limitation) on the yield attributes and grain yield of eight durum wheat cultivars. Eight defoliation treatments viz., i) control (no defoliation), ii) flag leaf blade removed, iii) flag leaf blade and the secondary leaf removed, iv) secondary leaf removed, v) spike awns and secondary leaf removed, vi) spike awns and flag leaf blade removed, VII) spike awns removed, and viii) Spike awns, flag leaf blade and secondary leaf removed were applied on eight durum wheat cultivars viz. i) Bani Suef 1, ii) Bani Suef 3, iii) Bani Suef 4, iv) Bani Suef 5, v) Bani Suef 6, vi) Sohag 3, vii) Sohag 4 and viii) Sohag 5. The study was comprised of wheat cultivars as the main plot while, defoliation (source and sink limitation) treatments as the sub-plots. Cultivars and treatments had significant effect on the number of grains spike-1, 1000-grain weight and grain yield. However, the highest grain yield was obtained from 'Bani-suef-1under all wheat defoliation treatment. On the other hand, the removal of spike awns and the secondary leaf treatment produced the highest 1000-grain weight and grain yield.

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