الفهرس 
TitleOnly 14 pages are availabe for public view
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Abstract
In the aim of production of new maize hybrids with a greater nitrogen use efficiency and balanced source-sink ratio, the objectives of the current investigation were to (1) Investigate of the morph-physiological changes in a new four maize hybrids during the early and rapid vegetative growth stages under deficient and sufficient N rates, (2) Assessment of the dynamics of critical physiological markers in C and N metabolism as leaf gradually moves from assimilation to remobilization modes during grain filling stage in these hybrids, and (4) Assessment of how differences in the morphological and physiological responses of these new hybrids relate to their nitrogen use efficiency and yield in N-sufficient and N-deficient soil. The new hybrids included Mo17 × B73, Sids7 × B73, NC358 × B73, and Tzi8 × Mo17, grown in the field for two consecutive years under two levels of N fertilizers: High N (285.7 kg N ha-1) and low N supply (71.4 kg N ha-1). Plant samples were harvested at various developmental stages including at 25 DAS (early vegetative, prior N application) and 50 DAS (late or rapid vegetative). Also, at flowering (” " ~ " ” 75 DAS), 30 plants for each hybrid were tagged and self-pollinated and their ear leaves were collected every 5 days through the first critical 20 days of grain filling period and finally at physiological maturity (110-120 DAS). The results of the present investigation can be summarized in the following points : 1- The new hybrids exhibited significant genetic variability in most of the tested parameters at early vegetative stage, which became more vigorous under sufficient and deficient N rate at late vegetative and during grain filling stages. 2- The tested hybrids showed a general reduction in all growth parameters and dry matter accumulation and remobilization, metabolites (photosynthetic pigments, sucrose, N fractions, amino acids, and enzymes), N accumulation and remobilization, and yield in response to N limitation and vice versa in response to N adequacy except starch, C/N ratio, secondary metabolites, asparaginase, and protease enzymes. Among hybrids, Tzi8 × Mo17 and NC358 × B73 exhibited alternative superiority over Sids7 × B73 and Mo17 × B73 for several of these traits. For some traits related to dry matter, Sids7 × B73 competed with the superior hybrids, particularly under high N supply. Mo17 × B73 maintained the lowest records of the above-investigated traits. 3- Kernels number per ear and ear weight were the most affected traits by N limitation. The percentage of low N-induced reduction in kernels number per ear for NC358 × B73 and Tzi8 × Mo17 were 40.7% and 26%, respectively, which was significantly lower than the other two hybrids. NC358 × B73 and Tzi8 × Mo17 had higher NUE and NUpE compared to Sids7 × B73 and Mo17 × B73, which attained the highest NUtE. Based on the above finding we recommend large-scale testing of hybrid NC358 × B73 under both N sets and hybrid Sids7 × B73 under high N input. On the other hand, testing hybrid Tzi8 × Mo17 under low N conditions.