Genetic Properties of Drought Tolerance Indices in Durum Wheat

A full-diallel cross of five durum wheat genotypes was made and grains of 20 F1s and their five parents was planted in two separate experiments, rainfall (stress) and irrigated (non-stress) in order to study the genetic properties of drought tolerance indices in durum wheat. The results revealed that some parents exhibited positive and high general combining ability, while some hybrids showed specific combining ability for the majority of these indices. There is uni-directional dominant effect for all traits excluding grain yield under stress conditions (Ys), yield index (YI) and yield reduction ratio (Yr). Scattering in dominant allels distribution in parents were found for all traits. There is dominant case in some single hybrids barring others for (Ys), (YI), geometric mean productivity (GMP) and stress tolerance index (STI). The estimates of gene effects revealed the significant role of additive genetic component ( D ) for Yr and STI. The non-additive component ( H l ) was higher as compared to ( D ) and the dominant genetic component ( H 2 ) was recorded with low magnitude than ( H 1 ) for all the traits. The average degree of dominance (√H 1 / D ) has been 1 for all traits. The ratio of the symmetry of the frequency of dominant and recessive alleles in all gene location controlling traits (H2/4H1) is less than 0.25 for all traits except Ys. All traits have shown above unity value for the proportion of dominant and recessive genes among the parents (KD/KR). The narrow sense heritability (Hns) was moderate for Yp (0.449), Ys (0.281) and MP (0.421), while high for remaining traits. Mid-parent heterosis was found to be positive for some hybrids in all traits. Mean productivity (MP), GMP, and STI were highly positive genetically correlated with each other as well as with Ys and grain yield under non-stress conditions (Yp).