| Abstract | This research was carried out at the Experimental Farm, Faculty of Agric., Kafr El-Sheikh Univ. The aim of the experiment was to study heterosis and combining ability for the most important traits of maize (Tasselling and silking dates, plant and ear heights, ear length, ear diameter, number of rows/ear, number of kernels/row, 100 grain weight and grain yield (ardab/fed.) Seven inbred lines of corn were crossed in one half diallel cross in 2004. The resulted 21 single crosses in addition to three recommended commercial crosses, were grown in a randomized complete block design in 2005 season. The variation among single crosses were partitioned into gca and sca, using griffing's method 4 model 1. The results are summarized as follows:
1.Highly significant differences were found among the studied inbred lines, also the gca effects were significant for all studied traits and the sca effects also, were, significant, except for 100-grain weight.
2. The cross (P5 x P6) was the earliest for tasseling and silking dates. The crosses (P3 x P7) and (P5 x P7) were of desirable performance for plant and ear heights. Mean while the cross (P1 x P2) was the best cross for ear length and number of kernels per row and grain yield/fed. and cross (P4 x P6) for ear diameter and number of rows/ear and the single cross (P1 x P4) for 100-grain weight.
3.The gca/sca ratio revealed that importance of additive genetic variance in the inheritance of all studied traits, except plant height and number of rows/ear.
4.The best general combining ability for earliness were lines P3, P4, P5, P6 and P7, while for grain yield ardab/fed. were lines P1, P2 and P3.
5.Estimate of specific combining ability effects indicated that the best crosses were 3 x 4 for tasseling date, silking date and ear height, the cross P2 x P7 for plant height, the crosses P3 x P6, P4 x P7, P4 x P6, P6 x P7 and (P1 x P3) for ear length, ear diameter, number of rows per ear, number of kernels per row and weight and 100-kernels, respectively, while the cross (1 x 2) showed the best desirable sca effects for grain yield ard./fed.
6.The cross (P 5 x P6) showed negative and significant useful heterosis for tasseling and silking dates relative to the earlier check, while the crosses (P3 x P7) and (P5 x P7) had negative and significant useful heterosis relative to the shortest check for plant and ear heights, respectively. The cross (P1 x P2) for ear length and number of kernels per row, (P4 x P6) for ear diameter and number of rows per ear, (P1 x P4) for weight of 100 kernels, and (P1 x P2) for grain yield ardab/fed. showed positive and significant heterosis relative to superior check in these traits.
7.The best cross (P1 x P2) was the superior one which significantly outyielded the three checks.
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