the impact of barley root structure and physiological traits on drought response

abstract drought is the most important factor limiting crop yield word wide. osmotic adjustment (oa) and strong and deep root system result in increased cereal drought tolerance through increasing water uptake and water use efficiency. the impact of root structure and physiological traits on drought stress response was studied in three barley cultivars including yousof (drought tolerant), morocco (susceptible), and fajr30 (semi-tolerant) and an iranian accession of wild species, hordeom spontaneum (tolerant). seeds were planted in pvc pipes 100 cm depth and 10 cm diameter. two moisture regimes applied including a normal irrigation at field capacity (control), and drought stress at 20% available water. root characteristics and physiological traits were measured ar flowering stage. drought stress reduced stomatal conductivity, rwc, leaf water potential, osmotic potential, oa and increased leaf temperature. minimum decline in leaf water potential, osmotic potential and rwc was observed in tolerant varieties (yousof and h. spontaneum). the tolerant and susceptible varieties showed the highest and the lowest oa. drought stress led to reduced root dry weight and volume in all varieties, susceptible variety showing the highest decline. root depth increased under stress in all tolerant and semi-tolerant cultivars, while decreased in the susceptible one. the results showed that tolerant varieties are varieties which could uptake more water by increasing root depth leading to higher oa and higher rwc. higher rwc results in more transpiration and lower leaf temperature under stress condition.