effect of root system and water use efficiency on grain yield and drought tolerance of bread wheat (triticum aestivum l.) genotypes

two glasshouse and field experiments were conducted to assess the effects of root system, water uptake, water use efficiency and early vigor on yield and drought tolerance of bread wheat in two successive farming seasons (2009-11). the experiments were conducted as randomized complete block design and two-year results analyzed as combined design. considerable genetic variation was observed among 40 genotypes for most of the traits. root length and water uptake showed significantly positive correlations with yield under drought stress condition (r=0.71** and r=0.47**, respectively) and drought tolerance score (r=0.67** and r=0.43**, respectively). moreover, genotypes with higher root length had higher water use efficiency and biomass (dry shoots and roots weight). water uptake had significant correlation with root system (root dry weight and length), above ground dry matter and water use efficiency. these correlations demonstrate breeding for a character may modify other traits simultaneously. stepwise regression analysis showed that the root length was the most important traits on yield under drought stress, followed by biomass, leaf length, water use efficiency and yield potential. based on two years results, mahdavi and akbari had the highest yield in drought stress and normal conditions, respectively.