Increasing plant density and improving N fertilizer rate along with the use of high density-tolerant genotypes would lead to maximizing maize (Zea mays L.) grain productivity per unit land area. The objective of this investigation was to match the functions of optimum plant density and adequate nitrogen fertilizer application to produce the highest possible yields per unit area with the greatest maize genotype efficiency. Six maize inbred lines differing in tolerance to low N and high density (D) [three tolerant (T); L-17, L-18, L-53, and three sensitive (S); L-29, L-54, L-55] were chosen for diallel crosses. Parents and crosses were evaluated in the 2012 and 2013 seasons under three plant densities: low (47,600), medium (71,400), and high (95,200) plants ha −1 and three N fertilization rates: low (no N addition), medium (285 kg N ha −1 ) and high (570 kg N ha −1 ). The T × T crosses were superior to the S × S and T × S crosses under the low N-high D environment in most studied traits across seasons. The relationships between the nine environments and grain yield per hectare (GYPH) showed near-linear regression functions for inbreds L54, L29, and L55 and hybrids L18 × L53 and L18 × L55 with the highest GYPH at a density of 47,600 plants ha −1 and N rate of 570 kg N ha −1 and a curvilinear relationship for inbreds L17, L18, and L53 and the rest of the hybrids with the highest GYPH at a density of 95,200 plants ha −1 combined with an N rate of 570 kg N ha −1 . Cross L17 × L54 gave the highest grain yield in this study under both high N-high-D (19.9 t ha −1 ) and medium N-high-D environments (17.6 t ha −1 ).

Among the phenotypic, biochemical, and molecular methods employed in assessment of genetic diversity, the phenotypic method has proven efficient for the assessment, description and classification of germplasm collections to enhance their use in maize breeding. The objectives of the present study were: (i) to assess the extent of genetic diversity in a collection of Egyptian commercial maize hybrids and populations, through field evaluation under water and N stressed and non-stressed conditions, using morphological data based on Principle Component Analysis (PCA), (ii) to measure the genetic distance among these genotypes using UPGMA cluster analysis and (iii) to assess the relationship between grain yield and yield-related traits of maize genotypes using GT-biplot analysis. A two-year field experiment was conducted in a split-split plot design with 3 replications, where 2 irrigation regimes, three N rates and 19 maize genotypes occupied the main plots, sub plots and sub-sub plots, respectively. The germplasm was assessed for 21 agronomic traits. Highly significant differences (P ≤ 0.01) were observed among the maize hybrids and populations for all measured traits.  Results of the GT biplot in the present study indicated that high values of 100-Kernel weight, ears/plant, kernels/plant, kernels/row, plant height, nitrogen use efficiency, nitrogen utilization efficiency, and grain nitrogen content and short ASI could be considered reliable secondary traits for improving grain yield under stressed and non-stressed conditions. The highest genetic distance was found between G9 (SC-2055) and each of G15 (American Early Dent), G18 (Midland) or G19 (Ried Type). The Agglomerative Hierarchical Clustering based on phenotypic data assigned the maize genotypes into five groups. The different groups obtained can be useful for deriving the inbred lines with diverse features and diversifying the heterotic pools.

Maize grain yield response to elevated levels of soil nitrogen is dependent upon genotype of the cultivar. Thus the optimum rate of N-fertilizer differs from maize genotype to another according to its nitrogen use efficiency (NUE). The main objective of this study was to determine the optimum Nrate for each studied inbred and hybrid that maximize grain yield. Six inbred lines of maize differing in their productivity under low-N were crossed in a diallel fashion to produce 15 F1ˊs. Parents and F1ˊs were evaluated in two seasons (2012 and 2013) using a split-plot design in randomized complete blocks arrangement with 3 replications. Main plots were allotted to four N-rates, i.e. 0, 80, 160 and 240 kg N/fed for N1, N2, N3 and N4, respectively. The sub-plots were assigned for the genotypes. Reducing N-level from 204 to 160, 80 and 0 kg N/feddan (fed) [one fed = 4200 m2] caused an increase in days to silking (DTS), anthesis silking interval (ASI), barren stalks (BS), economic NUEe and biological NUEb NUE and a decrease in the remaining studied traits including grain yield and its component. Maximum increase and decrease in traits occurred at N1 level (0 kg N/fed). The inbred lines L17, L18 and L53 proved to be tolerant (T), while L29, L54 and L55 inbred lines were sensitive (S) to N stress. The most tolerant crosses to low-N stress and the most responsive crosses to elevated levels of nitrogen were identified. Only two crosses (L18 × L53 and L18 × L55) showed high tolerance to low-N stress and responsiveness to high-N expressed in grain Original Research Article

Presence of G×E interaction reduces the correlation between genotypic and phenotypic parameters and complicates progress of selection. Among several methods proposed for evaluation of the GE interaction, the AMMI and GGE-biplot are the most informative models. The objective of this study was to estimate the G×E interaction in sorghum parental lines and to identify sorghum B-lines of stability and adaptability across different environments using the AMMI and GGE-biplot models. Six environments with 25 sorghum B-lines were conducted at two locations in Egypt (Giza and Shandaweel) in two years and two planting dates in one location (Giza). A randomized complete block design was used in each environment (yield trial) with three replications. The AMMI analysis of variance indicated that the genotype (G), environment (E) and GE interaction had significant Original Research Article

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