Combining Ability Analysis Using Diallel Crosses among Nine Inbred Lines of Corn under Two Nitrogen Levels

A half diallel cross between 9 inbred lines of maize was evaluated at two different nitrogen levels(60 and 120 kgN/fed.) for nine quantitative characters. Nitrogen level and crosses mean squares were significant for all traits under study. Significant crosses x nitrogen level mean squares were obtained for all studied traits except, No. of rows/ear. General and specific combing ability mean squares were significant for all traits, except days to 50% tasseling date. For days to tasseling  and no of rows/ ear at low nitrogen rate; silking at high nitrogen level; shelling% at high nitrogen level and combined analysis and plant height, ear height, no of kernels/ row, 100 kernel weight and grain yield/ plant in both and across nitrogen levels. High ratios which largely exceeded the unity were obtained, indicating that a large part of the total genetic variability associated with these traits was a result of additive and additive by additive gene action. For remain cases, GCA/SCA ratios were less than unity. Therefore, it could be concluded that the large portion of the total genetic variability for these traits was due to non-additive gene action. The parental inbred lines No. 1, 6 and 7 gave positive and significant () effects for grain yield/ plant and one or more of its components. The parental combination P₁xP₃, P₁xP₄, P₁xP₅, P₂xP₄, P₂xP₇, P₂xP_9, P₃xP_4, P₃xP₅, P₃xP₆,_, P₄xP_6, P₅xP₆, P₆xP₇, P₆xP_9, P₇xP₈ and P₇xP₉ for grain yield/plant exhibited significant positive  effects being 62.61, 20.37, 92.43, 42.37, 42.06, 17.94, 12.38, 10.57, 21.08, 53.52, 7.27, 14.95, 13.53, 42.00 and 49.83, respectively. The crosses 1x3, 2x7, 7x8, 7x9, 8x9 in low nitrogen environment, 1x3, 1x4, 1x5, 1x7, 2x4,  2x7, 6x7, 7x8, 7x9 and  8x9 at low nitrogen environment and 1x3, 1x5, 2x4,  2x7, 6x7, 7x8, 7x9 and  8x9 in the combined data gave the highest mean value of grain yield / plant.