The information on the nature and magnitude of gene action controlling important agronomic traits is essential for developing suitable breeding strategy. The present investigation was undertaken on rainfed lowland rice under normal and delayed transplanting conditions. The data were subjected to analysis of variance of compact family Block Design. Simple and joint scaling test and six parameters model of generation mean analysis were carried out to study nature and magnitude of gene effects. Simple and joint scaling tests indicated presence of epistatic gene interactions and fitness of digenic interaction model. Six parameter model of generation mean analysis revealed importance of additive (d) and dominance (h) gene effects as well as one or more of the epistatic gene interaction (I). Biological yield plant^-1 and plant height having high heritability and genetic advance in both transplanting conditions emerged as ideal traits for selection in both transplanting conditions. Grain plant^-1, tiller plant^-1, days to fifty per cent flowering in normal transplanting and harvest index in delayed transplanting indicated ideal traits for selection owing to their high estimates for both parameters in respective conditions.