الفهرس 
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Abstract
The present experiment carried out at the experimental in special Farm, during the three successive seasons. Seven common wheat varieties used to establish the experimental materials for this investigation. Those seven wheat varieties are Sids1, Gemmieza 7, Gemmieza9, Sakha 8, Sakha 93, Giza164 and Giza 168. Seven wheat varieties planted on November 2009. Crosses among the studied varieties made in first year. Grains collected and kept for the next year (2010/2011). In this year, hybrid grains planted with the seven parents for propagation. Using randomized complete block design with three replications. On the third year (2011/2012), two experiments designed; one had received normal irrigation, whereas the other one had received water only in two times. The first one at plantation the other had after forty-five days to test drought effect on agronomical characters in all tested genotypes.
Several agronomic characters recorded, those are:
Plant height (cm),main column spike length (cm),number of spikelets /main column spike, number of spikes /plant, number of grains / main spike, grain yield /plant (grain) ,1000-grain weight (gm.),heading date (days) and maturity date (days).
The obtained results summarized as follows:
1.1. Mean performance
Mean performance of the seven parents and their twenty-one crosses under normal irrigation, drought stress for all studied traits. General, the mean values of the normal irrigation condition found to be relatively better than that of drought stress in all studied traits under investigation. This affected the maturity date and maturity stages resulting to instability in wheat yield. In addition, the yield reduction of wheat under drought stress is associated with a less number of grains per spike and smaller grain size.
1.2 Variation and interaction with two different conditions:
Normal irrigation found to be significant for all studied traits. Genotypes and the resultant crosses found to be highly significant for all traits studied at the two different conditions indicating the wide diversity between the parental genotypes that used in the present study. Parents and crosses found to be highly significant for plant height, number of spikes per plant and heading date at the two different conditions. For number of spikelets per main column spike, spike length, 1000-grain weight, maturity date and number of grains per spike, the estimated values of Parent, and crosses were found be highly significant at normal irrigation while, significant only at the drought stress condition.
Results showed that genetic constitution of crosses as well as their parents is widely different and the crosses had a wide range of genetic variability. In addition, the interaction of genotypes with the two different conditions were found be highly significant for all studied traits indicating that these genotypes were inconsistent from condition to another. The interactions of the two conditions with parents found to be significant for all studied traits except for spike length and number of grains per spike.
2. Heterosis of morphological traits:
In fact, crosses would be of practical interest in hybrid breeding program because of their superiority in grain yield per plant and two traits contributing to yield, also heterosis for grain yield could be attributed to heterosis in number of spikes per plant and 1000-grain weight.
3.1. General combining ability effects:
It is of interest to note that the parent, Giza164, which possessed high general combining ability, effects for grain yield per plant, have also GCA effects for number of spikes per plant. In addition, Sakha8 and Sakha93 proved to be good combiner for heading date, maturity date, plant height, number of spikes per plant and number of grains per main spike.
The results obtained here concerning general combining ability effects could indicate that the excellent hybrid combinations obtained from the three possible combinations between the parents of high and low general combining ability effects, i.e. high × high, high × low and low × low. Consequently, it concluded that general combining ability effects of the parental lines were generally unrelated to the combining ability effects of their respective crosses.