الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 32 |  |  |
| | | from | 32 | | |
Abstract
The genetic materials used herein included six genotypes of wheat i.e., Misr1, Giza168, Shandaweel1, Gemmeiza9, Sids1 and Sakha 94. These genotypes were crossed in a half diallel cross mating design in 2010/2011 growing season at the experimental farm of Tag El-Ezz Agricultural Research Station in Dakahliea Governorate. The six parental genotypes and their 15 crosses were evaluated in 2011/2012 growing season under three nitrogen fertilization levels i.e., 25, 50 and 75kg N/fad., The aim of the present investigation was to determine the magnitude of both general and specific combining ability (GCA, SCA) and their interactions under three nitrogen fertilization levels for days to heading, days to maturity, grain filling period, plant height, main spike length, number of spikes/plant, number of grains per spike, 1000-grain weight, grain yield/plant and grain protein content (%). The mean squares for general and specific combining abilities were highly significant for all studied traits under the three different nitrogen fertilizer levels. Analysis of data also showed high GCA/SCA variance ratios, which exceeded the unity, suggesting that selection based on phenotype could be effective to improve and develop wheat genotypes concerning these traits under these conditions, where the additive genes were prevailed. The mean squares of interaction between nitrogen levels and both general and specific combining ability were significant for the studied traits. Generally, the obtained results showed that Gemmeiza9 proved to be good combiner for improving number of spikes/plant, 1000- grain weight, grain yield /plant and grain protein content under the three nitrogen fertilizer levels and Shandaweel1 for spike length, 1000-grain weight and grain protein content under the three different nitrogen fertilizer levels and Misr1 and Sids1 for number of grains per spike under the three nitrogen fertilizer levels. Some crosses had significant desirable SCA effects for yield, yield components and earliness traits and most of these crosses might be of great importance in breeding program for traditional breeding procedures under low nitrogen level in order to decrease nitric compound pollution in soils. Thus, the parental cultivars displayed enough of genetic variability. The significant of mean squares for parents vs. crosses provide evidence for heterosis. Moreover, nitrogen mean squares were significant indicating that these characters behaved differently from one nitrogen level to another. The cross combination (Shandaweel1×Gemmeiza9) gave the heaviest 1000-grain weight ant the maximum value of number of grains/spike and grain yield /plant was obtained by the cross ( P1×P5). The additive genetic variances (D) were significant for most of studied traits under three nitrogen fertilization levels. Significant values for the dominance components (H1) were obtained for all traits under three nitrogen fertilizer levels. Values of (H1) were larger in magnitude than their respective (D) ones for all traits under three nitrogen levels. N use efficiency characters, were studied among some Egyptian bread wheat varieties and their F1 crosses in order to detect the existed genetic variabilities and to examine their genetic behaviors under three nitrogen fertilizer levels.