Relationship between yield and yield components in Euroflour sunflower hybrid under water stress

To investigate the effect of water stress on Euroflour hybrid of sunflower, an experiment was conducted in research field of Tabriz Branch, Islamic Azad University. Experiment was carried out as a randomized complete block design with three replications. Water stress levels were irrigation after 50, 100, 150, 200 and 250 mm evaporation from class A pan. Based on the results, grain yield decreased 25%, 29%, 42% and 51% at irrigation after 100, 150, 200 and 250 mm evaporation traetments in comparison to the control (irrigation after 50 mm evaporation), respectively. Besides, oil yield percentage reduced up to 30%, 36%, 54% and 62% at irrigation after 100, 150, 200 and 250 mm evaporation treatments compared to the control, respectively.Increasing water stress decreased head diameter, 100 seed weight, seed kernel weight, number of filled seeds per head, biomass, chlorophyll content, leaf area index, relative water content, and oil percentage. Water deficit, on the other hand, increased seed hollowness and stomatal resistance. So, Euroflour is a susceptible sunflower cultivar to water deficit and any delayed irrigation will decrease yield through decreasing 100 seed weight and number of filled seeds per head which are the most important components of grain yield in sunflower.