Adaptive traits related to terminal drought tolerance in hexaploid wheat (Triticum aestivum L.) genotypes under field conditions

To identify and characterize bread wheat (Triticum aestivum L.) genotypes adapted to terminal water deficit conditions, 51 superior hexaploid wheat genotypes together with commercial check cultivars were studied, in a two stages screening practice, for drought tolerance in Karaj, Kermanshah, Isfahan, Neishabour and Varamin filed stations under terminal water deficit conditions in 2002-2005 growing seasons. At the first stage grain yield was the main criteria for screening, but several other traits including 1000 grain weight, number of tillers m-2, number of grains spike-1, spike and peduncle length were also measured. Glaucousness of leaves and stems (covered by grayish or bluish waxy coating) was assessed and recorded, two week after anthesis, in the second step. Results of the first step revealed 16 genotypes as superior as compared to the checks. In the second stage of evaluation 10 genotypes with grain yield of equal to or greater than 6 t ha-1 were identified where cv. Pishtaz had 5.7 t ha-1. Water productivity for some of the superior genotypes identified in the second stage was also measured in a separate experiment. The best genotype with good grain yield stability and high grain weight was WS-82-9 which also showed higher water productivity and is morphologically characterized between irrigated and rainfed adapted cultivars. This genotype had glaucousness on its leaves, in grain filling stage, which is a positive characteristic for tolerance to terminal moisture stress. It is concluded that growing of such cultivars with intermediate features (between rainfed and irrigated adapted cultivars), the yield gap between rainfed and irrigated wheat, to some extent, reduces and leads to enhancement of the average wheat grain yield in terminal drought prone areas.