الفهرس 
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Abstract
The field experiments of this investigation were carried out at the Experimental Stations of the Fine Seeds International Company (Bani Sweif Governorate) in two seasons. The objective of this study was to assess mean performance, combining ability, heterosis and genotype by environmental interaction for earliness, yield contributing, yield and its components in maize hybrids. The study comprised 40 maize genotypes (36 F1 hybrids and 4 commercial checks) were evaluated under six environments (E1, E2, E3, E4, E5, and E6) as a combination between three planting densities (24,000, 32,000, and 40,000 plants / feddan as normal, medium, and high) and two sowing dates (on April 10th and on May 28th as optimal and late). A split plot design with a randomized complete block (RCB) arrangement in three replications was used in this study. The main plots were assigned to three planting densities, while the sub-plots were assigned to maize genotypes. Sowing date (SD), planting density (PD), and their interaction (SD × PD) were highly significant for most studied traits. Highly significant differences were exposed for genotype (G) for all characters. Mean squares for genotypes (G), hybrids (H), and commercial cheeks showed significant and highly significant for all the studied characters under each plant density. The ratio of σ2 GCA/ σ2 SCA was a more than unity for earliness characters, ear site-plant, ear diameter, and number of rows per ear, indicating that additive genetic variances were predominant and played the major role in the gene expression of these traits. The rest of the characters are controlled by non-additive gene action. The 2nd sowing date had negative affected on all maize hybrids for all traits. Genotype G36 (L8 × L9) performed better under three planting densities during both sowing dates for grain yield. In general, the results showed that close relationship between per se performance of F1 crosses and their SCA effects under six environments for most studied traits, such that F1 hybrids ranking highest based on per se performance for these characters, also they show high SCA effects and vice versa. Joint regression analyses and AMMI analyses revealed significant genotype (G) and environmental (E) effects as well as GE interaction effect for grain yield. The analysis of variance explained 43.49% of the total grain yield variation by the environment, 35.02% by differences between genotypes, and 8.67% by GE interaction. Standard heterosis values ranged from -65.02 to 7.28% for grain yield (ardab/ feddan) over check variety Pioneer 32D99.