The present investigation was carried out at El-Gemmeiza Agricultural Research station, Agricultural Research Center (ARC), Egypt during four successive seasons from 2007/2008 through 2010/2011. Three crosses were used among five parental varieties, namely P1xP2 (1), P3xP4 (2) and P4xP5 (3) five populations (P1, P2, F1, F2 and F3) for each cross were used in this investigation. Highly significant heterotic values in positive direction were found for all charcters except for plant height and 1000-grain yield in the first cross, spike length in the second cross, and plant height, No. of grains/spike and No. of spikes/plant in the third cross. Over domenance for all characters except plant height and 1000-grain weight in the first cross, spike length in the second cross and No.of grains /spike in the third cross was detected. Inbreeding depression was obtained in two out of three crosses for spike length, No.of grains/spike, No.of spikes/plant, 1000-grain weight and grain yield/plant and in one out of the three crosses for plant height. The important roles of both additive and non-additive gene actionwere found in certain studied traits. Significant positive F2 deviation (E1) were indicated for plant height in the third cross, No.of spikes/pant and grain yield/plant in the second and third crosses and 1000-grain weight in the first and third crosses. High to medium values of heritability estimates were found to be associated with high and moderate expected and actual gain in most traits. These obtained results indicated that, these traits could be used in the early generations, but would be more effective if postponed to late generations.

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In order to study the effect of heterosis and nature of genetic on plant height and yield traits were studied in a 7x7 diallel cross without reciprocals and their F 2 generation in wheat to define and select an efficient and prospective material for immediate use in hybridization programs to improve grain yield of wheat in Egypt. Parents, F 1 and F 2 were evaluated for quantitative traits in 2016/2017 season. Significant genotype mean squares and its components (parents and crosses) were obtained for all traits in both generations. Significant heterosis in F 1 generation was obtained for all studied traits. Heterosis of grain yield/plant relative to mid parent varied from 4.64 to 75.50% in F 1 crosses. The P2xP3, P1xP4 and P2xP5 were the best crosses for grain yield heterosis. General (GCA) and specific (SCA) combining ability mean squares were significant for all traits. MS (GCA)/ MS (SCA) ratios indicated the relative importance of additive and non-additive gene action in their inheritance for all the traits. The nine crosses i.e. P1xP2,

In order to study the variations amongeset a half diallel cross using seven varieties for drought characters, estimating combining ability and genetic components. Two field experiments was carried out at the Experimental Farm of faculity of Agricultural-Tanta University during the two seasons 2016/2017 and 2017/2018, seven diverse wheat varieties (Triticum aestivum, L.) and 21 F1's were planted in two experiments. The first experiment was normally irrigated four times at different stages, the second one irrigated only once at tillering stage. The main results can be summarized as follow ; the water stress treatment decreased the means of flag leaf area (FLa), flag leaf angle (FLang), transpiration rate (TR), number of spikes/plant (NS/P), number of grains/spike (NK/S), 1000-grain weight (100-GW) and grain yield/plant (GY/P) for parents and their hybrids. The means of stomatal resistance (SR), chlorophyll a/b ratio (Chl a/b) and leaf temperature (LT) was increased under water stress. Irrigation mean squares were significant for all studied traits, indicating that the two irrigation regimes behaved differently for these characters. In addition, mean squares due to genotypes were highly significant for all traits except for FLA under stress condition.

In order to investigate the combining ability, gene action and heterosis morphological, yield and its components traits in wheat F 1 crosses using line x tester analysis. Experiment was conducted with sixty three genotypes consisting of fifteen lines, L