GENETIC STUDIES ON THE EFFECTS OF DROUGHT TOLERANCE AND EARLINESS ON GRAIN YIELD IN DURUM WHEAT HAVING DIFFERENT THERMAL RESPONSES

A diallel cross involving six durum wheat genotypes was evaluated to determine the genetic behavior of earliness components as well as yield and its components in durum wheat under irrigation and drought conditions. In addition, to drought susceptibility index, thermal unit and reduction percentage were calculated. The resultant hybrids along with their parents were evaluated in two experiments. The first experiment (stress) was irrigated once (70 days after planting while the second one (normal) was irrigated four times at Sids the experiment Station, Agriculture Research Centre. Genotypes mean squares were significant for most studied characters in the two experiments except for heading under normal experiment. GCA variance values were higher two or more times than the SCA variance one for most studied characters in both experiments, suggesting the predominant of additive and additive x additive gene action in controlling these characters. Parent P1 (Sohage1) could be considered as a good combiner for early heading and maturity under stress for days and thermal units; P2 (Sohage3) could be considered as a good combiner for early maturity under stress and normal of days and only under stress of thermal unit, while P3 (Beni Swief 6) could be considered as a good combiner for (early maturity under normal irrigation). Mareover, Parent P4( Portoroco) could be considered as a good combiner for grain yield /plant and kernel weight under stress and normal irrigation and susceptibility index for No. of spikes/ plant meanwhile, parent P5 (Quadrato) is a good combiner for grain yield/ plant, grain filling rate and No. of spikes/ plant of the two experiments and susceptibility index for both No. of kernels/ spike and kernel weight but parent P6 (Beni Swief1) considered a good combiner for grain yield/ plant and grain filling rate under two stress and normal irrigation and also early maturing of No. of days under only irrigation only. The best SCA values were detected for cross P1 x P 4 for the earliness of maturity (No. of days and thermal units) under stress water and the reduction percentage for number of days and thermal units of normal to stress conditions, grain filling rate, susceptibility index for No. of spikes/ plant, No. of kernels/ spike and kernel weight, and grain yield/ plant under both stress and normal conditions, crosses P1 x P 6, P 2 x P 6, P 3 x P 4 and P 3 x P 5 gave the best SCA effects for grain yield/ plant under both stress and normal conditions.