The investigation was laid out at the Experimental Farm of Rice Research and Training Center (RRTC), Sakha, Kafer EL-Sheikh, Egypt, during three successive rice growing seasons, 2010, 2011 and 2012.The study aimed to fin the effect of gene action in the inheritance of grain yield, its components and some rice grain quality traits under normal conditions. The materials for this study consisted of six rice genotypes namely; Sakha101, Sakha102, Egyptian Yasmin, GZ1368s-5-4, IET1444 and IR78875-176-B2-B, These genotypes have a wide range of variation due to their different genetic background. The six rice parents were crossed to produce F1 hybrid seeds of three crosses, namely, Sakha101 x GZ1368s-5-4, Sakha102 x IET1444 and Egyptian Yasmin x IR78875-176-2B. The six populations, P1, P2, F1, F2, BC1 and BC2 for each cross were utilized to determine the genetic parameter of the studied characters.
The results revealed that mid parent values (m) were highly significant in positive direction for all traits in all crosses, Moreover, additive effect was highly significant in negative direction for grain yield/plant trait in cross I, as well as, grain length, grain shape and amylose content % in cross II. In addition, dominance effect was played an important role in the inheritance of grain shape, and amylose % in negative direction and grain yield in positive direction in cross III. These results also indicated that all types of gene interaction were played an important role in the inheritance of all traits, according to the cross itself.
The broad sense heritability was high for all traits, it was ranged between (85.51 and 98.73%) for 1000 grain weight in cross I and grain yield/plant in cross I, respectively. Moreover, low to moderate estimated values of narrow sense heritability were observed for all traits in all crosses, the highest value (32.5%) was recorded for grain shape trait in cross III. However, the great discrepancy between the estimates of heritability in broad and narrow sense for 1000-grain weight character was reflected in low estimates of dominance variance or high estimates of additive variance for this trait. In addition, low estimates of expected genetic advance (9.03 and 9.04) were observed for amylose %, and 1000-grain weight in cross I, respectively. Low to moderate expected genetic advance with low narrow sense heritability for amylose content % and 1000-grain weight could be expected because this trait is under polygenic control. Moreover, additive and dominance components of variation were significant in the inheritance of these traits, but additive component was higher than the dominance one.
Conclusively, the results suggested that early generation selection may be effective in improving of these traits in cross I. On the other hand, the results also indicated that the selection in late generations will be improving grain shape in cross II and 1000 grain weight in cross III.