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The present study was carried out at the Experimental Farm, Faculty of Agriculture, Kafrelsheikh University, Egypt during 2011, 2012 and 2013 seasons. Three elite hybrid rice combination namely; IR64608 A x Giza 181, IR64608 A x Gz.1368-5-4 and IR64608 A x Suweon 287R were produced (in 2011) and evaluated beside their four parents (3 pollen parents and the iso genic maintainer of the CMS line IR64608 A) a long with seventeen rice cultivars/ or lines. Such genotypes including 7 of the most commercial rice cultivars, 3 drought tolerant rice varieties, six elite maintainers and IET 1444. All the materials (24 rice genotypes) were grown under two irrigation treatments; drought stress (irrigation every 12 days) and irrigation every 6 days through two successive seasons of 2012 and 2013. The aim of this investigation was to study the response of elite hybrid rice combinations to drought stress compared with a large number of Egyptian and exotic rice cultivars /varieties having a wide range of drought tolerance, determine the association between grain yield and the other agronomic characters under water stressed and non-stressed environments as well as estimate the range of drought susceptibility index for grain yield for the genotypes under study and to sheds light on phenotypic and genotypic coefficients of variability, heritability and genetic advance from selection. The genotypic variance (σ 2 G) was highly significant for all the studied traits, indicating wide range of genetic variability among rice genotypes. Also, the variance due to irrigation treatments (σ 2 T) was highly significant for all characters. Furthermore, G x T interaction was highly significant for all characters except for 1000-grain weight, indicating that the genotypes interacted considerably with environmental changes and 1000-grain weight was more genotypically controlled. The three hybrid rice genotypes involved in this study surpassed all the other genotypes in grain yield, number of panicles/ plant, number of grains/ panicle, number of spikelets/ panicle and panicle length. This was true under drought stress and over the two treatments. The hybrid rice IR64608 A x Suweon 287R recorded the most desirable estimates of grain yield (4.82 and 2.83 ton/fed.), number of grains/ panicle (231 and 160) and number spikelets/ panicle (255 and 205) under normal and drought stress, respectively. Grain yield was significantly correlated with each of panicle length, number of spikelets/ panicle and number of grains/ panicle under stressed and non-stressed environments. While, it was significantly correlated with days to 50% heading under drought stress and with number of panicles/ plant under higher moisture environment. The estimates of PCV was maximized in case of sterility percentage (42.9%) followed by number of panicles/ plant, while GCV values were maximized in case of number of panicles/ plant. The differences between PCV and GCV was high for number of grains/ panicle and grain yield, indicating the influence of environment on them but such differences were low in case of the other traits. High broad sense heritability estimates was recorded for days to 50% heading (94.3%), number of panicles/ plant (93.7%), panicle length (89.47%) and number of spikelets/ panicle (86.55%). The desirable genetic gain from selection was found to be associated with high heritability estimates in case of number of panicles/ plant and number of spikelets/ panicle. Moroberekan, Hexi 41B, IET1444, IR68884 B, WAB 878 and IRAT 170 detected the lowest DSI values however, their grain yield was still low compared with the hybrids and most of the other genotypes under drought stress.

PERFORMANCE, GENETIC VARIABILITY, AND TRAITS ASSOCIATION OF HYBRID RICE UNDER NORMAL AND DROUGHT ENVIRONMENTS