Combining Ability Analysis Using Diallel Crosses among Eight Inbred Lines of maize under Two Planting Dates

A half diallel cross between 8 inbred lines of maize was evaluated at two different planting dates for nine quantitative characters. Planting dates and crosses mean squares were significant for all studied traits. Mean squares due to crosses x planting dates were significant obtained for most studied traits. General (GCA) and specific (SCA) combing ability mean squares were significant for all traits. High ratios which largely exceeded the unity for days to 50% tassling and silking, plant height, ear height, no of rows/ ear , no of grains / row and 100 kernel weight were obtained, indicating that a large part of the total genetic variability associated with these traits indicates that of additive and additive by additive gene action. For remain cases, GCA/SCA ratios were less than unity, therefore, it could be summarized that the most percentage of the total genetic variability for these traits was due to non-additive gene action. For plant height, ear height and grain yield/ plant, the ratio of SCA x D/SCA was higher than GCA x D/GCA. This result indicates that non- additive effects were more influenced by sowing date than additive genetic effects for this trait. P1 seemed to be the best general combiner for early maturity, short plants, low ear position, grain yield/plant and some of its components in the combined analysis of both sowing dates. The parental combination P1xP3, P1xP5, P1xP7, P2xP4, P2xP5, P2xP7 , P3xP4, P3xP5, P3xP6 , P3xP4, P6xP7 and , P7xP8 for grain yield/plant exhibited significant positive  effects being 13.54, 14.68, 12.79, 21.81, 21.61, 9.15, 21.64, 27.34, 7.36, 6.37 and 33.49, respectively