الفهرس 
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Abstract
Two field experiments were carried out in Agric. Expt. Farm at Shalakan, Kaluobia Governorate, Cairo, Egypt during 2010/2011 and 2011/2012 growing seasons to study the Response of three bread wheat cultivars to sowing date. Each experiment included 15 treatments which were the combination between five sowing date and three wheat cultivars. The experimental design used was split plot design in 6 replications. The main plots were occupied by five sowing dates (October 1st, October 16th, November 1st, November 16th and December 1st). The three wheat cultivars namely Sakha 93, Giza 168 and Gemmiza 9 were distributed randomly in the sub-plots. br The weight of blades was in highest values at heading stage followed by marked decreases by advancing the plants towards maturity stage. The substantial decreases in blades dry weight could be mainly attributed to differentiation of spikes and translocation of photosynthetic assimilates -#102;-#114;-#111;-#109; vegetative to reproductive organs. The accumulation of dry matter in spikes was significantly the highest for wheat cultivar Gemmiza 9. br At harvest, Gemmiza 9 exhibited the tallest plants, highest spikes No/m2, Main spike length and weight as well as grain No/main spike, grain , straw, biological and GCP yields, NUE, NRE GCPC, wet and dry gluten as well as gluten hydration percentage; test weight and 1000-grain weight. The studied traits were greatly affected by genetic make-up of the studied cultivars. It was found a positive relationship between GCPC, vitreosness, wet gluten content; test weight and 1000-grain weight. br Sowing wheat plants at 1st November exhibited statistically maximum dry weight of blades, stems + sheaths and spikes in comparable to early and late sowing in the season. It was generally noticed a remarkable reduction in percentage of blades and stems + sheaths by advancing the plants towards maturity stage. On the contrary, the highest spikes yield either absolute amount or percentage of total plant biomass was found when the plants were sown on 1st November. br Sowing on 1st November had remarkable effect on rising NUE, NRE and NPE; yield components including plant height, spikes No/m2, main spike length and weight as well as grain No/main spike that affected positively on grain, straw, biological and grain protein yields. br Test weight and 1000-grain weight were significantly and gradually increased versus late sowing date of wheat till reached its maximum value by sowing on 1st November. It was cleared that the dry weight of vegetative organs of wheat cultivar Gemmiza 9 exhibited significant maximum dry weight of blades, stems + sheaths and spikes under different growth stages. The dry matter accumulated in plant organs were markedly and significantly decreased versus early sowing date. On the other hand, the decrease in the above traits was monitored at late sowing but by less extent as compared to early sowing. The dry weight of spikes was markedly increased reaching their maximum values at physiological maturity stage. br The dry matter partitioning showed different trend. The percentage of blades and stems + sheaths was markedly decreased by advancing the plants -#102;-#114;-#111;-#109; booting towards maturity stage. These decreases were corresponded with substantial increase in spikes percentage reaching their maximal values at physiological maturity stage. br At harvest, Gemmiza 9 exhibited maximum tallest plants, highest spikes No/plant; length, weight and grains No/main spike at all studied sowing dates reaching their maximum values when sown on 1st November. The high performance of cultivar Gemmiza 9 in yield attributes was positively reflected on its yield and grain technological parameters. br The interaction between sowing dates and studied wheat cultivars affected significantly nitrogen physiological parameters. The data cleared that all the three studied cultivars gave maximum values of NUE, NRE, and NPE by sowing on 1st November. Gemmiza 9 exhibited maximum value of NUE and NRE in comparison to the other two cultivars grown under the same date. br -#102;-#114;-#111;-#109; the above mentioned data, the author recommended that bread wheat cultivar Gemmiza 9 was the best adapted cultivar and could be grown on 1st November under the environmental conditions of Kaluobia Governorate.