Four rice genotypes differed in drought tolerance were crossed. Six populations (P1, P2, F1, F2, BC1 and BC2) of two rice crosses namely; Sakha 102 x IR 83142-B-60-B- (cross I) and Giza 159 x Takanari 1 (cross II) were raised in a randomized complete block design during the three successive summer seasons from 2014 to 2016 at the farm of Rice Research Agricultural station, Sakha, Kafr El-Sheikh, Egypt. This study aimed to determine heterosis, gene action, heritability, genetic advance and phenotypic correlation response to select and predict by the new lines for some root traits (Root length, Root volume, Number of roots/plant and Root/Shoot ratio %) and some grain quality traits. Flush water irrigation was added every 12 days intervals. The results indicated that highly significant and positive heterosis as a deviation from mid- and better- parent were obtained for all root and grain quality, except for grain shape in the first cross and for grain length in the second cross which showed highly significant and negative estimates of heterosis as a deviation from mid-parent. In addition, incomplete dominance to over-dominance was operative for most of the studied traits.
Additive gene effect (d) and dominance gene effect (h) were more important in the genetic system for all the studied characters, additive x additive gene effects (i), additive x dominance (j) and dominance x dominance (l) gene effects were involved in the genetic control of all characters, except some exceptions. Heritability in broad sense was high in most traits of the two studied crosses, except cross I for root/ shoot ratio under normal condition. The highest value of heritability estimates (95.95 %) was recorded for root volume in the cross I under normal condition. The narrow sense heritability was moderate to low in most traits of the two crosses. High values of predicted genetic advance were estimated for most traits of the studied traits. Significant or highly significant positive phenotypic correlation was found between most of the studied characters for the two studied crosses especially between root and grain quality characters with grain yield/ plant, except amylose content trait.
In general the cross Giza 159 x Takanari 1 could be grown under water deficit for further screening and selecting desirable root and grain quality traits at the same time.