Two field experiments were conducted at the Experimental Farm, Gemmeiza Agriculture Research station, Agricultural Research Center white maize (ARC), Egypt during two growing seasons (2014 and 2015), to study the response of two maize hybrids i.e., white maize single cross 128 and yellow maize single cross 176 to four nitrogen fertilizer levels i.e. 0, 45, 90 and 135 kg N/fad., and three phosphorus fertilizer levels i.e. 0, 15.5 and 31 kg P 2 O 5 /fad. Concerning the obtained results, SC 128 outyielded SC 176 in grain and biological yields (combined data) due to superiority in days to 50% tassiling and silking, leaf chlorophyll content, ear leaf area, leaf area index, relative photosynthetic potential for stover yield/plant, ear length and diameter, stem diameter, number of grains/row, hundred grain weight as well as grain and stover yields/plant, while SC. 176 gave the highest mean for each of plant height and relative photosynthetic potential for grain yield/plant. No significant differences among maize hybrid could be detected in relative photosynthetic potential for biological yield/plant, number of rows/ear, ear leaf efficiency and migration coefficient. Data of combined analysis revealed that addition of nitrogen (N) fertilizer and raising its rate up to 135 kg N/fad., was accompanied by asignificant increase in each of leaf chlorophyll content (mg m-2), plant height, leaf area index (LAI), ear length and diameter, stem diameter, number of rows/ear, number of grains/row, hundred grain weight, grain and stover yields/plant, ear leaf efficacy and migration coefficient, but relative photosynthetic potential for both stover and biological yields/plant were decreased. Increase of phosphorus (P) level up to 31 kg P 2 O 5 /fad., was followed by a significant increase in grain yield/fad., and almost all their attributes, but relative photosynthetic potential for both stover and biological yields/plant were decreased. Meantime, ear diameter responded to phosphorus addition up to 15.5 kg P 2 O 5 /fad., however, days to 50% tassling and silking were not significantly affected by varying phosphorus levels according to combined analysis. In almost cases, maize hybrid SC. 128 was more efficient and more responsive than SC. 176, where the former was is need to 135 kg N/fad., and 31 kg P 2 O 5 /fad., in order to maximize the grain yield to only 42.8 ardab/fad.

Two field experiments were conducted at Gemmeiza Agriculture Research Station; the first was under normal irrigation and the second was under water stress by skipping the third and fourth irrigations during the two seasons 2018 and 2019, to study the response of 16 maize hybrids to water stress. A strip plot design with four replications was used in each year. Combined analysis across two years revealed that, significant or highly significant differences were detected between two years for the most of traits. Highly significant differences were found between normal irrigation and water stress treatment for all studied traits. Hybrids showed highly significant differences for all studied traits. The highest single crosses for grain yield plant-1 were SC 128 followed by SC 132 under normal irrigation and water stress conditions, meanwhile the highest three-way cross was TWC 321 under normal irrigation and TWC 368 under water stress. Single crosses SC 178 and SC 176 also three-way crosses TWC 352 and TWC 368 were able to tolerate drought. Correlation coefficient was significant and positive between each of ear length and number of kernels row-1 with grain yield plant-1 under normal irrigation and between 100 kernel weight and grain yield plant-1 under normal and stress irrigation.

Combining ability for grain yield and other traits were evaluated in a half diallel fashion in maize. Eight yellow maize inbred lines were crossed in half diallel fashion excluding the reciprocals during the summer season of 2018 at Gemmeiza station, the resulting 28F1 were evaluated along with check SC168 at two locations (Gemmeiza and Sids) in 2019 summer season. A randomized complete block design (RCBD) with four replications was used. Mean squares of GCA and SCA were highly significant for all the studied traits at combined data, except SCA for ear diameter. The non-additive gene effects were most responsible for controlling the inheritance of days to 50% silking, plant height, ear length and grain yield. While the additive gene effects had the important role in the inheritance of ear height and ear diameter. The parents; P6 and P7 were significant for general combiner for yield and p4 for earliness. The crosses P3 xP7, P5 x P8 and P6 x P7 had desirable SCA effects for earliness. Meanwhile, the crosses P2 xP8, P3 x P6, P4 x P5 and P5 x p7 showed high SCA effect for grain yield. The single crosses; P2 xP7, P2 x P8, P3 x P6, P5 x P7, P6 xP7 and P7 x P8 had desirable mean values for earliness and grain yield.