The present investigation was carried out at the Experimental Farm Research, Station of Nubaria during three successive seasons starting 2002/2003 through 2004/2005 to evaluate grain yield, its components and some growth traits in five inter varietal crosses of bread wheat (Triticum aestivum L.)and their six populations (P1, P2, F1, F2 Bc1 and Bc2).
Significant positive heterotic effects referring to the better parent were detected for days to heading in all crosses except for the first cross, number of spikes plant-1, number of grains spike-1 and spike weight in all crosses, grain yield plant-1 in the second, third and fifth crosses and 1000-grain weight in the fifth cross only. However, negative heterotic effects were detected for plant height in all crosses, grain yield plant-1 in the first and fourth crosses, 1000 – grain weight in all crosses except the fifth one.
Inbreeding depression estimates were significant for all crosses except the third cross for days to heading. There were overdominance effect towards the higher parents for days to heading in the first and fifth crosses, number of grains spike-1 and spike weight in all crosses except the fourth cross and grain yield in the first and fifth crosses. Partial dominance towards the lower parents for plant height in the second and fourth crosses, grain yield plant-1 in the fourth cross only, 1000 – grain weight in the second and third crosses. Additive gene effects were positive and significant for number of spikes plant-1 in the fourth and fifth crosses, grain yield plant-1 in the third and fifth crosses, 1000 – grain weight in the first, second and third crosses, respectively. Additive x additive gene action was significant for heading date in the first, second, fourth and fifth crosses and grain yield plant-1 in the first cross only. Both the F2 deviation (E1) and backcross deviation (E2) were significant for most characters. Heritability estimates in broad sense ranged from 4.22% for grain yield plant-1 in the first cross to 82.19% for 1000-grain weight in the fourth cross, however heritability in narrow sense ranged from 39.66% for number of grains spike-1 in the second cross to 96.08% for number of spikes plant-1 in the first cross. Low to high genetic advance were found to be associated with low to high narrow sens heritability estimates in all studied traits.