Background and objective: Investigation on genetic variability and correlation study between yield and its components of genotypes on rice may increase the opportunity to exploit its potential which will help meet the demand of high grain yield and nutrition supply. The current study aimed to determine correlation and path coefficients between twenty-two Egyptian and exotic rice genotypes to establish selection criteria which might help to develop genotypes for high yielding. Materials and methods: Twenty-two Egyptian and exotic rice genotypes were evaluated through seven agronomic traits. Agronomic data were collected during the two successive rice growing seasons, 2017 and 2018. The matrix of phenotypic correlations was estimated and analyzed into direct and indirect effects through path coefficient analysis. Results: Results showed that grain yield per plant had a high positive and significant correlation (p ≤ 0.01) with panicle number per plant, full grain number per panicle, and 1000 grain weight, 0.791**, 0.670**, and0.766**, respectively. As expected, there was a negative correlation (p ≤ 0.05) between days to heading and panicle number per plant (r =-0.496*) and with1000 grain weight (r =-0.433*). Path coefficient analysis showed that despite high positive and significant correlation (p ≤ 0.01) between grain yield per plant and many variables, a small number of these correlations was verified to have a relationship of cause and effect. Variables with positive and significant correlation and with a high direct effect on grain yield per plant were 1000 grain weight (0.5107 direct effects) followed by panicle number per plant (0.4003), and full grain number per panicle (0.3028). Conclusion: The three traits (1000 grain weight, panicle number per plant, and full grain number per panicle) are the most important variables for use in grain yield per plant assessment programs as selection indices because they have positive and significant correlations and direct and/or indirect effect on the correlation value of the increased rice grain yield production. Hence, for increasing grain yield, the direct selection of genotypes based on positively correlated traits will be more fruitful while planning any rice breeding program to achieve higher grain yield in rice.
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...
Six rice genotypes with different drought tolerance were crossed. Six populations (P1, P2, F1, F2, BC1 and BC2) of three rice crosses namely Giza 177 x Giza 178 (cross I); Sakha 103 x WAB 880 SG 33 (cross II) and Sakha 104 x IET 1444 (cross III) were raised in a randomized complete block design with three replications during the three successive summer seasons from 2010 to 2012 at the Farm of Rice Research and Training Center Sakha, Kafer El-Sheikh, Egypt. This study aimed to determine the heterosis, gene action, heritability, genetic advance and phenotypic correlation response to selection and prediction by the new lines for the traits of days to 50 % heading, plant height, panicle length, number of panicles/ plant, number of filled grains/ panicle, 100-grain weight, sterility % and grain yield/ plant. Flashing water irrigation was added every 10 days intervals. The results obtained from the mean of parents, F1 and F2 generations showed wide range in mean values between the parents and the presence of partial and overdominance were found for all studied characters. Significant and highly significant positive estimates as a deviation from mid and better parents in all crosses for panicle length, number of panicles/ plant and grain yield/ plant, also highly significant positive estimates as a deviation from mid and better parents in the first two crosses for plant height. Scaling test provide evidence of non-allelic interaction in controlling all the characters studied in most crosses, the additive gene effect (d) was more important in the genetic system for all studied characters, dominance gene effects (h) and additive x additive gene effects (i) were played an important role in the inheritance of plant height, panicle length, number of filled grains/ panicle, 100-grain weight, sterility % and grain yield/ plant. The additive x dominance (j) were significant and involved in the inheritance of days to 50 % heading, plant height, number of panicles/ plant, number of filled grains/ panicle, 100-grain weight, sterility % and grain yield/ plant. However, the dominance x dominance (l) were involved in the genetic control of all characters. Heritability estimates in broad sense were high. Meanwhile, heritability estimates in narrow sense were mostly low. The maximum genetic advance of the mean values was found to be high for number of panicles/ plant, plant height and days to 50 % heading characters. Highly significant and positive correlation was found for grain yield/ plant with panicle length, number of panicles/ plant, number of filled grains/ panicle and 100-grain weight in all studied crosses. From the foregoing results, cross II (Sakha 103 x WAB 880 SG 33) and cross III (Sakha 104 x IET1444) could be recommended for growing under water deficiency to obtain the highest rice grain yield and the highest values of saving water at the same time.
Rice breeders are encouraged to classify potential F1-hybrids without crossing all viable mixtures by testing depending on genetic distance due to lack of labor and time in yield trials. The goals of this research were to establish heterosis and investigate the relationship between genomic distance and agronomic attributes under drought. Half-diallel mating design, 28 F1′s and 8 parents were evaluated under drought and genotyped using 11 microsatellite markers. In total, 39 alleles were detected. Results indicated that the greatest heterotic effects for grain yield were observed in Sakha 103 × Sakha 104 and GZ7576-10-3-2-1 × Giza 179, which gave 29.32–22.57% heterosis, respectively. Heterosis for grain yield in these crosses occurred as a rise in panicle weight, filled grains per panicle, low sterility and 100-grain weight. Correlations of marker-based genetic distance with mid-parent heterosis were positively and significantly correlated with sterility percentage (r = 0.390 *, p < 0.05). However, better-parent heterosis was positively and significantly correlated with sterility percentage (r = 0.352 *, p < 0.05) and grain yield per plant (r = 0.345 *, p < 0.05). Associations indicate that high grain yield and low sterility of rice crosses can be expected from microsatellite marker-defined distances of parents. This study indicated that genetic distance is very effective for heterosis prediction in breeding programs.
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