The main objective of this study was directed to evaluate combining ability
effects of exotic lines, and to determine the mode of gene action, which control, grain
yield and its components, as well as some morphological and earliness traits of yellow
maize. Thus, four exotic yellow maize inbred lines were top crossed with two local
populations as testers. The results from the evaluation of these genotypes revealed
that Lines differ in their order performances, when crossed with each of male parent
(tester). All top crosses showed Significant heterotic effect over their mid and better
parents for ear length, number of kernels per row, 100 kernels weight and grain yield
per plant. Line 1 (Mv 0.9) proved to be a good general combiner for earliness, ear
height, ear diameter, number of rows per ear and grain yield per plant. Whereas, line
2 (Mo 17) was the best general combiner for tallness, ear length, number of grain/row
and gr combiner for tallness and most of yield component trcits, The results showed that the magnitudes of additive genetic variance were
positive and lower than those of non additive genetiC variances for 50% silking, plant
height and yield and its components. This fact could be verified by the dominance
degree ratio, which was more than one for all traits, indicating that over dominance
played a major role in the inheritance- of these traits. The promising top crosses,
which resulted from exotic lines and local tester exhibited desirable specific combining
ability (SeA) effects and high heterotic values. Therefore, these superior crosses offer
a good chance for possibility of improving yellow maize in Egypt