الفهرس 
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Abstract
The present investigation was carried out during 2010 and 2011 rice growing seasons at the Research Farm of Rice Research and Training Center (RRTC), Sakha, Kafr El-Sheikh, Egypt, to study: 1- The mean heterosis effect as a deviation from both mid-parent and better-parent. 2- General and specific combining ability effects. 3-Phenotypic correlation coefficients among all possible pairs of the studied traits, under water stress and normal conditions. Six rice genotypes namely; Giza177, Sakha101, Asucena, IR78875-176-B-2-B, IR81025-B-2-7-3 and IR80508-B-194-1-B were crossed in all possible combinations excluding reciprocals according to Griffing (1956), method (2), model (1). All genotypes (six parents and their 15 F1 crosses) were planted under both normal irrigation (irrigation every four days) and drought conditions (drought stress was imposed by using flush irrigation every 12 days without standing water after irrigation) in a Randomized Complete Block Design (RCBD), with three replications. characters were investigated and divided into two main groups as follows: A- Root and vegetative traits: Number of tillers/plant; days to heading (days); plant height (cm); root length (cm); root volume (cm3), and root: shoot ratio. B- Yield and its component traits: Panicle weight (g); panicle length (cm); number of primary branches panicle-1; 1000-grain weight (g); grain yield/ plant (g), and drought susceptibility index (DSI). The statistical analysis was done using Method 2, Model 1 (fixed model) of Griffing (1956) which is a fixed model and was considered most appropriate as its all requirements were met by experiment. Conclusion and recommendation: Based on the previous results it can be concluded that six crosses namely; crosses no. 2 (Giza 177 X AZUCENA), no. 3 (Giza 177 X IR 7887-176-B-2-B), no. 10 (AZUCENA X IR 7887-176-B-2-B), no. 11 (AZUCENA X IR 80508-B-194-1-B), no. 12 (AZUCENA X IR 81025-B-347-3) and cross no. 14 (IR 7887-176-B-2-B X IR 81025-B-347-3) were the lowest crosses affected by water stress (more tolerant to drought), were the best cross combinations in yield and most yield components traits under drought conditions, as well as these crosses were the best crosses in specific combining ability and the most superiority over mid and better parents heterosis. Therefore, this study recommends the cultivation of these six crosses and enter them in rice breeding programs to improve grain yield trait under drought stress condition. Also, it could be concluded that yield ability under drought stress condition could be achieved through selection for each of plant height, panicle weight and panicle length traits.