The purpose of the study was to evaluate the relationship between the genetic (GD) and phenotypic (PD) distance of parents and the specific combining ability (SCA) and mid – parent, heterosis, (MP).
The experiment comprised (8) cultivers of tetraploid wheat (Triticum durum Desf.) and (15) hybrids obtained by crossing in a (line× tester) scheme. Parents and hybrids were planted in the botanic experimental station, in the Agricultural and Forestry Collage of Mosul University, conducted in a randomized complete block design (R. C. B. D.) with three replications during the growing season (2010 – 2011), (2011 – 2012). SCA as well as at mid parent heterosis (MP) were estimated for quantitative characters, GD and PD values were investigated between pairs of parental genotypes. GD was evaluated by using randomly amplified polymorphic DNA markers. The ratio between the general combining ability components to that of the specific one revealed that the non-additive genes effects were more important in the inheritance of all the studied characters. Most of hybrids showed desirable or highly significant (SCA) and heterotic values at (MP) for most studied characters. As well as, a highest genetic distance determined between cultivars; 3(Azeghar– 1) and 6 (Acsad– 65) and the lowest between cvs. 2(Leeds) and 4(Doma– 1) by using (Nei and Li 1979). (Non-significant correlations were observed between genetic distance (GD) as well as (PD) with both: the amount of SCA and heterosis for grain yield, wherase the correlation coefficient between(GD) and heterosis for these characters had apositive and significant value.