الفهرس 
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Abstract
Consistent with production of high yielding maize hybrids under low N input, the objectives of the current investigation were to (1) evaluate the growth, physiological and yield responses of a set of four elite maize inbreds along with two of their single cross hybrids under sufficient and deficient N inputs,(2) evaluate and compare the heterotic estimates of critical phenotypic, physiological, and yield traits in the selected hybrids under sufficient and deficient N supply and (3) investigate the genetic diversity among the selected inbreds in a key N metabolism related genes. The selected inbred lines included the two Egyptian inbreds (Sids7, Sids63) and two American inbreds (B73, Mo17). On the other hand, single cross hybrids including Sids7 × Sids63 and B73 × Mo17 were produced and used. The evaluation processes were carried out of field grown inbred and hybrids under sufficient N input (Normal: 120 kg /N feddan) and limited N supply (30 kg N feddan). For growth, physiological and yield evaluation, samples were harvested at various developmental stages including V4 (15 DAS, referred as initial), V8 (45 DAS, about two weeks before flowering), R1 (60 DAS, flowering) and R6 (physiological maturity). The results of the present investigation can be summarized in the following points: (1) The tested inbreds exhibited significant natural differences in most of the tested parameters at initial stage where the single-cross hybrids of these inbreds tended to show non-significant natural differences in most of their initial related parameters. In both inbreds and hybrids, the above natural differences became more vigorous under sufficient and deficient N rates. (2)The tested genotypes (inbreds & hybrids) showed a general reduction in all growth parameters and biomass accumulation, metabolites and yield in response to N limitation and vice versa in response to N adequacy. Among inbreds, B73 and Sids7 exhibited alternative superiority for several growth parameters and biomass accumulation and yield up to 45 DAS whereas Sids63 competed with them at later growth stages. On the other hand, Mo17 maintained the lowest efficiency. For the investigated hybrids, the Egyptian hybrid Sids7 × Sids63 had superior growth parameters and higher biomass accumulation, metabolites and yield under sufficient and limited N supply at major developmental stages. Based on the combined results of molecular analysis: (1) DNA fragments from the promoter region of AS gene from the tested inbreds were successfully amplified, sequenced, aligned and analyzed. The tested inbreds were divided into two distinct groups: the first group includes the American line B73 and the Egyptian line Sids7 whereas the other group involves the American line Mo17 and the Egyptian line Sids63.