Main Article Content
Knowledge on combining ability and type of gene action of available germplasm would help maize breeder in identifying proper parents and breeding procedure for improving plant density tolerance (PDT). A split plot experiment with three replications was carried out; where plant densities were devoted to main plots, namely low density (LD), medium (MD) and high (HD) density (47600 to 71400 and 95200 plants/ha, respectively) and subplots to genotypes. Both GCA and SCA variances were necessary for the expression of studied traits under all plant densities, but the magnitude of δ2SCA was much higher than that of δ2GCA for most studied traits, suggesting the predominance of non-additive gene effects in controlling inheritance of the most studied traits under all plant densities. Lines were the highest contributor to the total variation under all densities (HD, MD and LD). For grain yield under increased plant density, the best general combiners were L28, IL51, L21, L17, L14, IL84, IL15 and IL53 and the best test crosses in SCA effects were IL84 × SC10, L21 × Sd7, IL151 × Giza 2, IL51 × Giza 2, IL15 × Sd7 and L17 × Giza2. This germplasm could be used in future plant breeding programs for improving maize PDT. Based on the SCA effects of crosses under HD, the three testers successfully classified 15 out of 23 tested inbred lines into three heterotic groups: Five inbreds belong to heterotic group-1, five to heterotic group-2, while the remaining five belong to heterotic group-3; these three groups can maximize heterosis by crossing inbred lines belonging to different heterotic groups/unrelated lines.