This investigation aimed to study the potentiality of heterosis expression, heritability, expected genetic advance, nature of gene actions and potance ratio for some quantitative traits (grain yield and its contributory characters, heading date and plant height) in two bread wheat crosses Sids 1 x Gemmeiza 5 and Gemmeiza 9 x Sids 4 were chosen for the percent study on the base of wide variability. Six populations (P1, P2, F1, F2, BC1 and BC2) were used to estimate genetic parameters under two levels of nitrogen fertilization (35 kg N/fed and 70 kg n/fed).
The results can be summarized as follows:
The hybrid combination Sids 1 X Gemmeiza 5 was detected to be the highest cross showed significant useful heterosis for grain yield per plant (37.58% and 76.11%) under 35 kg.n. /f and 70 kg.N./f, respectively.
Inbreeding depression values were found to be highly significant in most cases in the two crosses under investigation.
3. The F2-deviations (E1) were significant for plant height and number of spikelets / main culm spike for all crosses under the both of nitrogen fertilization levels. Also backcross-deviations (E2) were found to be significant for heading date, main culm spike length, number of spikelets / main culm spike and number of kernels per spikelet under the two levels of nitrogen fertilization.
The additive gene effects (a) were found to be significant for heading date, plant height and 1000 grains weight for all crosses under investigation under the two levels of nitrogen fertilization.
Dominance gene effects (d) were found to be significant in the two crosses for number of spikelets/main culm spike under 35kg.N./f only.
The three epistatic types additive × additive, additive × dominance and dominance × dominance were found to be significant for most traits under investigation.
High heritability estimates in broad sense were detected for nearly all traits studied. high estimates of narrow sense heritability were found for all crosses for heading date, plant height, number of spikes per plant, main culm spike length, number of kernels per spikelets, number of kernels per main culm spike and grain yield per plant under 35 kg.N./fed.
High genetic advance under selection was found to be associated with high narrow sense heritability estimates for number of spikes per plant and grain yield per plant for all crosses under 35 kg.N./f.
The breeder can use cross Sids 1 X Gemmeiza 5 in breeding programs that it has high heterosis for yield character and its components and high genetic advance under selection was found to be associated with high narrow sense heritability estimates for number of spikes per plant and grain yield per plant.