SABRAO Journal

Parental lines, namely: F1, F2, BC1, BC2, BC11, BC12, BC21, BC22, BC1 selfed, and BC2 selfed generations of three crosses involving six cultivars of durum wheat (Triticum durum Desf.) were studied for awn length under normaland late-sown environments to analyze the nature of gene effects and components of heterosis (over the better parent). A sixparameter model in the cross Cocorit 71 x A-9-30-1 in the normal-sown condition and a 10-parameter model in most of the cases were found adequate under both environments to explain the inheritance of this trait, indicating a greater role of epistatic interactions. Additive (d) gene effect was frequently observed to be more significant than the dominance (h) gene effect. Of the epistatic interactions, digenic and/or trigenic interactions played significant roles in controlling the inheritance of this trait. Nonfixable gene effects were higher than the fixable gene effects in all the crosses in both sowing environments, indicating the significant role of nonadditive gene effects in the inheritance of awn length. Significant positive heterosis (over the better parent) was observed in the cross Raj 911 x DWL 5002 under the normal-sowing environment. Significant heterobeltiosis in this cross is attributed to the major combined effects of additive x additive x dominance (x) and dominance x dominance (l) gene effects. Absence of significant heterosis in other cases could be due to the internal cancellation of heterosis components. Significant inbreeding depression was observed in the crosses HI 8062 x JNK-4W-128 and Raj 911 x DWL 5002 in the normalsowing environment. Duplicate type of epistasis at digenic level was observed in the cross Raj 911 x DWL 5002 in the normal sowing environment, hence, selection intensity should be mild in the earlier generations and intense in the later generations. Biparental mating in segregating generations and/or diallel selective mating in diverse parents, which exploits both fixable and non-fixable components, is suggested for the improvement of this trait in durum wheat. A restricted recurrent selection, by intermating the most desirable segregants, followed by selection might prove to be a useful breeding strategy for the amelioration of this trait in durum wheat.