Combining ability analysis was calculated for grain yield and some yield related traits in rice through 8 x 8 diallal set analysis excluding reciprocals at the Experimental Farm of Sakha Agricultural Research station Kafr El-Sheikh, Egypt during 2016 and 2017 summer seasons under normal and water stress conditions. Mean squares of Parents and their crosses were highly significant for all traits studied under both environments and their combined analysis, indicating that overall wide differences among these populations and reflecting the diversity at the parent and their crosses for the studied traits.
GCA and SCA mean squares were found to be highly significant for all traits studied under both environments indicating that the role of additive and non – additive gene action in the expressions of these traits. The ratio of GCA/SCA was less than unity for all traits under both environments, except for grain yield /plant under stress condition, indicating that non – additive gene action was more responsible for the inheritance of these traits. The variety IRAT 170 and Morobroken could be used as a good combiner parents for grain yield /plant and some of its components under normal as well as stress conditions due to its significant and/or highly significant (gi^) in positive direction while the parental varieties; Giza 177, Giza 178 and Giza 179 behaved as good combiner for No. of days to 50% heading under both environmental conditions. The crosses; Sakha 106 x Giza 179, Giza177 x IET1444, Giza 177 x Morobroken, Giza178 x Giza 179, Giza 178 x Morobroken and IET 1444 x Morobroken had significant () in positive direction under normal condition for grain yield and some of its components. While the crosses; Sakha 106 x Giza 177, Sakha 106 x Giza 179 and Giza 178 x Giza 179 had significant () in positive direction for grain yield and some of its components under stress condition.