Effect of drought stress on seed yield and some morpho-physiological traits of sunflower

To investigate the effect of water stress on morphological and agronomical characteristics of sunflower (oilseed hybrid Allestar)، an experiment based on randomized complete block design was conducted with three replications at the Experimental Station of Islamic Azad University، Tabriz branch. Water stress was applied as irrigation after five evaporation levels (50، 100، 150، 200 and 250 mm) from evaporation pan class A. Results showed that، increasing water stress significantly decreased head diameter، number of seeds per head، 100- seed weight، oil percent، harvest index، leaf area index and seed yield. Mean seed yield decreased from 4460، kg ha-1 in control (50 mm) to 3460، 3200، 2210، and 1810 kg ha-1 for 100، 150، 200، 250 mm evaporation، respectively. It was also revealed that leaf area index was the most sensitive morphological trait to water deficit and was declined significantly by increased drought stresses. Any delayed irrigation resulted in reduced crop yields through shortened reproduction period، reduced number of seeds produced and inability of assimilate transportation for seed filling.