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Abstract
Enhancement of maize productivity from land unit area in Egypt could be achieved via growing tolerant hybrids to high plant density (HD) stress in combination with using the optimum plant density and appropriate nitrogen fertilization rate. A set of inbred lines with obvious diversity in their adaptive traits to HD and low-nitrogen (LN) were used in the present study as parents of diallel crosses (without reciprocals) to study the inheritance of these traits, identify tolerant genotypes to HD and LN stresses and determine the optimum plant density and adequate N-fertilization for maximizing grain yield/fed (GYPF). A split-split plot design in randomized complete blocks arrangement with 3 replications was used, where main plats were devoted to N levels (low; 0 kg N, medium; 120 kg N and high; 240 kg N/fed), sub-plots to plant densities (20, 30 and 40 thousand plants/fed) and sub-sub plots to maize genotypes. Some newly developed maize hybrids that characterized by more ears/plant (EPP), high harvest index (HI), high economic nitrogen use efficiency (NUEe), narrow leaf angle (LANG), short anthesis-silking interval (ASI), less barren stalks (BS) and less plant height (PH) and ear position (EP) gave very high grain yield, reaching 60 ard/fed (ca. 20 t/fed) in the cross L17 {u00D7} L54, when were grown under high plant density (40,000 plants/fed) and were given the recommended N fertilization rate per plant (6 g N). GYPF of all studied genotypes showed a quadratic response of increase to the nine environments from low to high levels, except L29, L54 and L55 inbreds, which showed a quadratic response of decrease. The inbreds L17, L18 and L53 proved to be tolerant (T), while L29, L54 and L55 were sensitive (S) to HD and/or LN