A half diallel cross between eight common bread wheat varieties and/or lines (Triticum aestivum L.) was evaluated under three different nitrogen rates for six quantitative characters in RCBD with three replications. Nitrogen rates, genotypes, parents, hybrids, genotypes x nitrogen rates interaction and hybrids x nitrogen rates mean squares were significant for all traits under study. General and specific combing ability mean squares were found to be significant for all traits. High ratios which largely exceeded the unity were obtained for all studied traits except grain yield/plant in low and normal nitrogen fertilization rates indicating that large part of the total genetic variability associated with these traits was additive and additive by additive gene action. For the exceptional case GCA/SCA ratios was less than unity, therefore, it could be concluded that the large portion of the total genetic variability associated with this case is due to non-additive gene action. The largest heterotic magnitude express by the previous traits. May strength ened the conclusion about the 9 importance of non-additive gene effects in their inheritance. For grain yield/plant; eight, ten, eight and sit crosses expressed significant and positive (Sij) effects in zero, low, normal nitrogen levels and the combined analysis, respectively. However, the most desirable (Sij) effect were recorded for the crosses 3 x 6, 1 x 8, 2 x 4, 6 x 7 and 5 x 6 in the respective cases. Also, the cross 1 x 2 (8.40**) in zero nitrogen level, 2 x 4 (13.14**) in low nitrogen level and 1 x 8 (22.10**) in normal nitrogen level ranked the first best (Sij) effects in the respective cases. |
