Two field experiments were carried out in Agric. Expt. Farm at Shalakan, Kaleobia Governorate, Cairo, Egypt during 2010/2011 and 2011/2012 growing seasons to study the response of some bread wheat cultivars to sowing dates. Each experiment included 15 treatments which were the combination between three wheat cultivars (Giza 168, Sakha 93 and Gemmiza 9) and five sowing dates (1st October, 16th October, 1st November, 16th November and 1st December). The experimental design used was split plot design in 6 replications. The data revealed that sowing dates and cultivars both significantly affected wheat yield and its components. Sowing on 1st November exhibited significant maximum plant height, number of spike/m2, main spike length and weight, grains number of main spike as well as grain, straw and biological yields as compared to early or late sowing in the season. Concerning wheat cultivars, Gemmiza 9 gave significantly highest yield and its components in comparison to Sakha 93 and Giza 168. The effect of the interaction between wheat cultivars and sowing dates were significantly differed in plant height, main spike length and weight, grain weight/spike as well as grain, straw and biological yields as well as GCPY. Gemmiza 9 exhibited the significant highest parameters when sown on 1st November as compared to the other studied two cultivars. The data revealed that sowing Gemmiza 9 wheat cultivar on 1st November was the most suitable environmental conditions for growing wheat in Kaluobia Governorate.

The objectives of this study were to examine the relationship between wheat yield cultivars (Sakha 93 and Giza 168) and antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and phenylalanine ammonia-lyase (PAL) activities under different soil water content i.e. low, moderate and high content by Irrination at 806/6 ETo (1280m'/fed.), by, 100% ETo (1600m'/fed.) and120% ETo (1920m'/fed.), respectively. Two lysimeter experiments were carried out in two successive seasons i.e. 2006/2007 and 2007/2008 to estimate wheat yield and one experiment in plastic bags carried out of the greenhouse to determine the antioxidant enzymes of 28 days wheat plant under three different soil water content i.e. providIng wheat seedlings with aforementioned treatment. Exposing wheat cuitivars i.e. Giza 186 or Sakha 93 to water stress by Irrigation at 80% ETo (1280 m3/fad.) exerted an increase in CAT, SOD, POD, APX and PAL over those irrigated at 100% ETo (1600 m'/fad.) or at 120% ETo (1920 m'/fad.), but the previous enzyme activities in the tissue of Saka.93 surpassed of that of Giza 168 cuitivar. spike weight and weight of 100 grain/plant of Sakha 93 cuitivar overcome that of Giza 168 at low soil moisture content (80% ETo), whereas opposite results were obtained at high and moderate water content (120% and 100% ETo) in the first growing season (2006/2007) and spike weight/plant in second growing season (2007/2008). There was a proportional relationship between increasing soil moisture content and grain yield/plant but the difference between moderate water content 100% ETo (1600 m'/fed.) and high water content 120% ETo (1920 m3/fed.) was not significant. Providing 28 days wheat plant with low water content, decreased wheat yield/plant and its attributes comparing with moderate water content for the two studied cuitivars. The current study indicates that Sakha 93 cultivar was the most tolerant cuitivar compared with Giza 168.