The present investigation was conducted to determine the magnitudes of combining ability and heterosis obtained from hybrids three produced by utilization of CMS, maintainer and restorer lines in rice. The experiment was carried out during the two growing seasons of 2010 and 2011 at Rice Research and Training Center (RRTC) Farm, Sakha, Kafr El-Sheikh, Egypt. Twelve F1 hybrids were obtained from crossing three CMS lines as female parent with four restorer lines. These hybrids were evaluated along with their parents for genotypic variances. The analysis of variance revealed highly significant differences among genotypes, parents, parents vs. crosses for days to heading (day); plant height (cm); panicles plant-1 ; panicle length (cm); filled grains panicle-1 ; spikelets fertility% and grain yield plant-1 except parents vs. crosses for panicle length (cm). The variance among males (testers) were either significant of highly significant for all studied traits. The variances among crosses due to males and females (lines x testers) interactions, showed highly significant SCA effects for all the studied traits except for plant height (cm). The estimated values for variance of general combining ability (σ²GCA) were less than specific combining ability variance (σ²SCA) for all studied traits except plant height (cm). This result indicated the preponderance of non-additive gene action. It was supported by the ratio of (σ²GCA/ σ²SCA) which was less than one for all studied traits except for plant height (cm), indicating that the non-additive type of gene action played a major role in the inheritance of these traits. Heritability estimates in broad sense (h 2 b%) were high for all studied traits. However, heritability estimates in the narrow sense (h 2 n%) were moderate for days to heading (day) (44.58%), plant height (cm) (45.81%) and filled grains panicle-1 (53.80%) and low for the other traits. Three parental lines viz.; IR69625A; G46A and GZ9057-6-1-3-2 were identified as good general combiners for grain yield plant-1 (g). Hybrid combinations as G46A x Giza178; IR69625A x GZ6296-12-1-2-1-1 and Large stigma A x GZ9057-6-1-3-2 showed high mean performances due to the presence of SCA effects.

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Four maize hybrids (122, 168, 173 and pioneer) were investigated to determine their genotypic effects on callogenesis response to 2,4-D (2,4 dichlorophynoxyacetic acid) and in vitro salt tolerance using NaCl. A callus was initiated from mature embryos cultured on three MS media supplemented with 0, 2 and 4mg/l of 2,4-D where the level 0 is the control. The produced calli from the medium which contains 2 mg/L 2,4-D for each genotype were then exposed to four salinity levels (i.e. 0, 1500, 3000 and 6000 ppm) of NaCl, respectively to evaluate some physiological aspects of the produced calli from the genotypes. The results of ANOVA revealed that the mean squares of genotypes at all levels of 2,4-D were significantly indicated the presence of differences between them for all in vitro traits. Furthermore, the mean squares of levels and genotype × levels interaction were highly significant for all traits. This indicated that these genotypes gave different responses at different 2,4-D levels. The genetic variation was high and positive with respect to the in vitro traits at each 2,4-D level. This indicated that these traits are mainly controlled by genetic factors. This finding was emphasized by the heritability values, which were more than 80% for all studied traits at each 2,4-D level. In relation to callus response to salt stress, the results indicated that the presence of significant differences between these genotypes for ion content in callus cells (K + %, Na-%), organic solutes accumulation (sugars and proline), membrane permeability and relative growth rate as well as water content with respect to the four levels of salinity. This finding is emphasized by the heritability values, which were more than 80% for most of studied traits.

In Egypt, as well as many other countries, corn is considered an important field crop. Due to the importance of corn, scientists in all countries gave corn breeding great concern. Many authors obtained high values for heterosis from the F1 maize hybrids. It is found that the amounts of heterosis from the MP % for the diallel cross mating design were: 179.30, 17.78, 51.97 and 52.77% for Ear weight, No. of rows/ear, No. of kernels/row and 100 kernels weight at Mansoura location, respectively. The values of heterosis were: 107.13, 9.06, 31.07 and 65.30% for the same traits at the second location (Sohag), respectively. However, the estimated amounts of heterosis with respect to t BP % were: 152.48, 3.79, 26.36 and 38.7% for Ear weight, No. of rows/ear, No. of kernels/row and 100 kernels weight at Mansoura, respectively. They were: 68.70,-1.32, 23.05 and 51.12% for the same traits at Sohag, respectively. But for the line x tester mating design, it is appeared that the amounts of heterosis from the MP % were: 51.14, 3.20, 11.7 and 44.60% for ear weight, No. of rows/ear, No. of kernels/row and 100 kernels weight at Mansoura, respectively. The values of heterosis were: 121.1, 19.0, 42.6 and 50.17% for the same traits at Sohag, respectively. ًWhile the estimated amounts of heterosis with respect to the BP % were: 26.33,-16.13, 1.92 and 24.32% for ear weight, No. of rows/ear, No. of kernels/row and 100 kernels weight at Mansoura, respectively. They were: 89.7,-4.2, 5.5 and 21.82% for the same traits at Sohag, respectively. GCA and SCA are usually used to estimate the types and the nature of gene action that present within hybrids. In this respect, there are different mating designs are known to obtain the estimates for these two components. Among these mating designs i.e. diallel crosses and line x testers mating designs. These two mating designs yield estimates for both GCA and SCA. The mean squares for GCA at Mansoura were highly significant for No. of kernels/row and 100 kernels weight. In general, the magnitudes of the mean squares at Sohag were larger than their corresponding estimates at Mansoura for Ear weight and No. of rows/ear while, it was the vice versa for No. of kernels/row and 100 kernels weight. The mean squares of the GCA of all yield component traits were larger in their magnitudes than their corresponding estimates of SCA at Mansoura. It is found that the results for the line x tester mating design indicated that the mean squares of GCA were highly significant. Therefore, both additive and additive by additive genetic variance appeared to be the most important and reliable component of genetic variances. The presence of significant estimates of GCA and SCA suggest the importance of either additive (GCA) or non additive gene action (SCA). Indeed, superior hybrids depend on the presence of dominance genetic variance. In the same time, superior hybrids would depend on additive by additive genetic epistasis in case of the absence of the dominance variance. Therefore, it is very important to estimate the two ...

The main objective of this study was to study the genetic behavior for some Japonica rice varieties in Egypt. An experiment was conducted to evaluate the performance of 15 F1 hybrids along with their parents i.e Giza177; Sakha101; China2; IR67701B; GZ8479-6-2-3-1 and GZ7955-13-2-1-1 in rice by using a half diallel analysis mating design at Rice Research and Training Center (RRTC) Farm, Sakha, Kafr El-Sheikh, Egypt during 2010 and 2011 growing seasons. Analysis of variance revealed highly significant differences among genotypes; parents and crosses for days to maturity (days); plant height (cm); panicle length (cm); spikelets panicle-1 ; panicles plant-1 ; panicle weight (g); 1000-grain weight (g); spikelets fertility% and grain yield plant-1 (g). Both general and specific combining ability variances were found to be highly significant for all studied traits. The ratio of σ 2 gca / σ 2 sca values were less than unity for all studied traits indicating the preponderance of non-additive genetic variance in the inheritance of these traits. High broad sense heritability estimates were observed for all studied traits suggests high component of heritable portion of variance, which is the portion exploited by rice breeder and that selection for these traits can be achieved directly based on their phenotypic performance. While, heritability estimates in narrow sense was relatively low for the same traits. According to the mean performance for the studied traits, cluster analysis divided the six rice parental varieties into tow major group based on days to heading (day), plant height (cm), spikelets panicle-1 and spikelets fertility%.