الفهرس 
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Abstract
The research presented in this thesis was designed to: 1)- Study the effect of water stress on different maize traits. 2)- Test the genotypic differences among many maize genotypes in drought tolerance and to identify the best ones. 3)- Evaluate the role of general and specific combining ability of inbred lines in hybrid performance under water stress conditions. This study was carried out at the Experiments Station of the Faculty of Agriculture, Mansoura University, during 2012 and 2013 summer seasons.In 2012 summer growing season, the six maize parental inbred lines were crossed in all possible combination excluding reciprocals by using a half diallel crosses mating design to obtain 15 single crosses. The fifteen F1 single crosses were evaluated at 2013 growing season under two irrigation treatments in 2 separated fieled trials. Irrigation treatments were normal irrigation every 12 days (normal), and irrigation every 18 days (water stress). Each experiment arranged in Randomized Complete Blocks Design (RCBD) with 3 replications in the 2013 growing season.The following measurements were recorded: A- Flowering and vegetative traits: Anthesis date, silking date, anthesis-silking interval (ASI), ear leaf area/plant, plant height, ear height,. B- Yield and yield components: Number of ears/plant, ear length, ear diameter, number of rows/ear, number of kernels/row, 100-kernel weight, ears yield per plant, grain yield per plant, shelling percentage, and C-Quality traits: Crude protein percentage and oil percentage.Data recorded from experiments conducted in 2013 maize growing season were subjected to statistical analysis using randomized complete block design (RCBD) with three replicates for each experiment, as described by Gomez and Gomes (1984). Data of all 15 single crosses at each irrigation treatment were analyzed as randomized blocks. The sum of squares of crosses was partitioned to general and specific combining abilities, following method 4 model 1 (fixed effects) of Griffing (1956).Based on the previous results it can be concluded that the cross No. 1 (P1 x P2) under well irrigation conditions, and the cross No. 2 (P1 x P3) under water stress conditions, were the best cross combinations in yield and most yield components traits under such conditions, as well as the best crosses in specific combining ability and the most superiority over commercial hybrids under the study conditions. Therefore, this study recommends the cultivation of these hybrids and enter them in maize breeding programs to improve yield and quality under drought conditions.