This investigation aimed to study combining ability and heterosis through a
half diallel cross mating design in Gemiza maize population using six S5 parental lines
to produce fifteen crosses. The data were recorded on ten quantitative characters t.e,
grain gield/ plant, ear length, ear diameter, number of rows!ear, number of kemels!
row, 100- kemel - weight, plant height, ear height, tasseling date, and silking date.
Combining ability were estimated according to Griffing's procedure (1956). Meth0d-4-
model-I. The results showed that, Generally, the best crosses (G2 x G6), (G3 x G4)
and (G3 x G5) for grain yield! plant and its components, and towards earliness; and
crosses (G2 x G4) and (G4 x G5) for plant height (towards shortness and ear height
(twards low ear placement) Genotypes mean squares showed highly significant
differences for all studied traits. Significant estimates of specific combining ability
(S.CA) along with insignificant (G.C.A.) variances were detected for grain yield/plant,
ear length, ear diameter, number of kemeVrow, 100-kemel-weight and plant heights,
revealing that non-additive type of gene action was the more important part of the total
genetic variability for these traits. For other traits i.e, silking and tasseling dates
exhibited high G.CA! S.CA ratios which exceeded the unity indicating the
predominance of additive gene action in the inheritance of such traits. Desirable
significant (G.CA) effects (gi) were obtained by G3 and G5 for number of rows! ear;
G4 for plant height, G5 for ear height (towards shortness); and G3 and G4 for
tasseling and silking dates (towards earliness). Estimates of specific combining ability
(S.C.A) effects (Sij). Generally, the best crosses were (G3 x G4), (G2 x G5), and (G1
x G6) these crosses may be of prime importance in breeding programmes for hybrid
maize production providing that the additive genetic system present in the good
combiner as the complementary and epistatic effeds that act in the same direction to
reduce undesirable plant characteristics and maximize the character in view. The
crosses showed non-significant heterotic effects either positive or negative values for
the check variety (Sc. 129) where the heterotic values ranged from (6. 18% to
18.77%) positive values and (-2. 56% to 37.49%) negative values.