Line by Tester Analysis for Estimats Combining Ability in Bread Wheat Under Different Levels of Nitrogen Fertilizer

Ten genotypes of bread wheat were crossed in a line x tester mating design. The twenty-one F1's and their parents (seven lines and three testers) were estimated under three levels of nitrogen fertilizer; low (25 kg N/fed), mid (50 kg N/fed) and normal (75 kg N/fed) in three experiments. Each experiments in a randomized complete block design with three replications at the Experimental Farm, Faculty of Agriculture, Menoufia University, Shebin El-Kom, Egypt during 2019/2020. The results cleared that nitrogen fertilizer levels mean squares were significant for all studied traits. A significant difference was found among lines, testers, line x testers and their interaction with nitrogen levels for all studied traits. Analysis of genetic revealed that GCA and SCA variances were significant for all studied traits under different levels of nitrogen fertilizer, indicating the importance of both additive and non-additive components in the inheritance of these traits. However, the hybrids L1 x T1, L2 x T1, L2 x T3, L3 x T2, L4 x T2, L5 x T2, L6 x T2, L7 x T1and L7 x T3were excellent harmonious combiners for specific combining ability effects for grain yield per plant and most of its components under different nitrogen fertilizer levels. The parental lines 1, 4, 6 and 7 proved to have better general combiners for grain yield per plant and most of its components under different levels of nitrogen. Therefore, these genotypes must be taken care of when breeding to tolerate low levels of nitrogen fertilization.