Study of Water Stress Effects on Water Use Efficiency and Drought Tolerance of New Sunflower Cultivars

To investigate sensitivity indicators of five new sunflower cultivars under water stress conditions in terms of drought tolerance (DT) and water use efficiency (WUE), a split plot experiment based on the randomized complete block design (RCBD) with three replications was conducted in 2020 in the Braun Area of Isfahan Province, Iran. The surface irrigation treatments included three levels based on evaporation from class A evaporation pan: 90 (no-stress), 120 (mild stress), and 150 mm (severe stress), as the main factor, and sunflower hybrids Chiara, Oscar, Fantasia, Hysun33, and Shams, as the secondary factors. Indicators such as economic yield (EY), biological yield (BY), WUE, harvest index (HI) and DT were analyzed. The highest rates of HI (43%), WPe (4854 kg.ha-1), and BY (13457 kg.ha-1) were obtained from no-stress treatment, followed by 120 mm treatment. Among the cultivars, Fantasia variety with BY equal to 12268 kg.ha-1, economic yield (4081kg.ha-1), and HI of 43% had the highest values. The highest WUE was obtained in the conditions of mild stress and severe stress  equal to 0.85 and 0.72 kg.m-3, respectively. Among sunflower cultivars, the highest WUE belonged to Hysun 33 with 1.04 kg.m-3. Fantasia with 0.96 kg.m-3and Shams with 0.84 kg.m-3 ranked next. Also, the lowest values of WUE were related to Oscar and Chiara cultivars with values of 0.81 and 0.75 kg.m-3, respectively. In total, deficit irrigation in the 120 mm treatment had the least negative effect on yield and harvest index, and it was suitable in terms of WUE. Finally, Fantasia showed the highest BY, DT, and HI with suitable WUE.