A Study on combining ability and heterosis were conducted on 15 F1 hybrids along with eight rice genotypes (five lines and three testers) to understand the pattern of inheritance of yield, its components and some root traits for selecting superior genotypes. The experiment was carried out using line x tester mating design, during 2010-2011 rice growing seasons at the experimental farm of Rice Research and Training Center, Sakha, Kafr El-Sheikh, Egypt. Analysis of variance revealed significant differences among genotypes, lines, testers and line x tester interactions for days to 50% heading, plant height, panicle length and weight, number of filled grains/panicle, number of panicles/plant, number of roots/plant, root length and volume and grain yield/plant traits under water stress conditions, indicated that the genotypes had wide genetic diversity for the studied traits. Significance of the means of sum squares due to lines and testers indicated a prevalence of additive variance. However, significant differences due to interactions of line x tester for the above mentioned traits, indicating the importance of both additive and non-additive variance in the inheritance of these traits. The mean squares due to GCA as well as SCA were significant for all studied traits except 100-grain weight and root/shoot ratio. Thus, the significance of GCA (variances due to lines and testers) and SCA (variances due to lines x testers) implied that both additive and non-additive types of variation was available for all the traits, yet additive genes were more important than the dominant genes because variance due to GCA was higher than that of SCA for all mentioned traits. Moreover, the ratio of GCA and SCA variances was greater than unity for all the traits studied that revealed the preponderance of additive gene action over the nonadditive gene action. IET 1444, Morobrekan and Giza 178 rice genotypes were the best general combiners due to highly significant GCA effects for number of roots/plant, root volume and root length traits. Moreover, Wab 450-JR-4-1-1 as tolerant to water stress conditions was the best general combiner for panicle weight, number of filled grains/panicle, otherwise, Sakha 102, rice genotype was the poorest combiner comparing with other rice genotypes for all the studied traits, except days to 50% heading. The crosses, Sakha 105 x IET 1444, Sakha 103 x Sakha 102 and Morobrekan x Wab 450-JR-4-1-1 were found to be the best cross combinations for most of the studied traits; these crosses had high and significant SCA in desirable direction under water stress conditions. Highly significant and positive estimates of heterosis and heterobeltiosis were recorded in Morobrekan x IET 1444, Sakha 105 x IET 1444 and Sakha 104 x Sakha 102 for number of panicles/plant, panicle length and number of roots and their volume/plant, respectively. The highest estimated values of phenotypic (Vph) and genotypic (Vg) variances were observed for number of filled grains/panicle, root number/plant and root volume indicating better scope...

Water limit is one of the major a biotic stress limiting plant production in worldwide. The research work of the present study was carried out at the Experimental Farm of the Rice Research and Training Center (RRTC), Sakha, Kafr El-Sheikh, Egypt, during the three successive rice seasons 2010, 2011 and 2012, to study the genetic effects on some of root system related to water limit and yield and its component traits under water limit condition. Six rice genotypes i.e. Giza 177, Sakha 101, GZ 7456-13-6-5-3, Sakha 105 (sensitive to drought stress), IRAT 112 and IRAT 170 (tolerant to drought stress), were chosen for this study. The results of this investigation revealed that both general and specific combining ability variances were found to be highly significant for all studied traits except root thickness, root dry weight and 1000-grain weight, indicating the importance of both additive and non-additive genetic variance in determining the inheritance of these studied traits i.e. root length, root volume, plant height, No. of days to heading, , No. of panicles/plant, No. of filled grains/panicle and grain yield/plant. With the exception of No. of panicles/plant and grain yield/plant, the GCA/SCA variances were found to be greater than unity for all the studied traits except for No. of panicles/plant and grain yield/plant, suggesting greater importance of additive genetic variance in the inheritance of these traits. Therefore, it could be concluded that selection procedures based on the accumulation of additive effect would be successful in improving of these traits. The results showed that IRAT 112 and IRAT 170 were highly significant and positive general combining ability effects for maximum root length, root thickness, root volume, root dry weight and yield and its component traits under water limit condition indicating that these genotypes could be considered as good combiners for the improvement of these traits i.e. Sakha 105 x IRAT 112 for maximum root length, Sakha 101 x IRAT 112 for root thickness, Giza 177 x IRAT 112 for root volume, IRAT 112x IRAT 170 for root dry weight and Sakha 101 x IRAT 170,Sakha 101 x IRAT 112 for grain yield/plant under water limit condition. Frequency distribution of phenotypes for each trait in F2 and their parents, all studied traits approximately fit normal distribution, F2 plants having phenotypic values greater than the higher parent and less than the lower parent (Transgressive Segregates) were observed for all studied traits.

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Salinity is a common abiotic stress that seriously negatively affects rice production in the world. The investigation was carried out at the Experimental Farm of El-Sirw Agricultural Research Station, Damietta governorate, Egypt to investigate the effect of soil salinity levels (6 and 11 dS m -1) on the morphological, leaf chemical constituents and yield traits and phenotypic and genotypic parameters of twelve rice genotypes (