Evaluation of morphological, physiological, and photosynthetic responses of sunflower cultivars (Helianthus annuus L.) under different irrigation regimes

In order to determine the water requirement of sunflower cultivars, an experiment was conducted during 2015-2016 at Ardestan Station, Isfahan. The experiment was carried out in a factorial randomized complete block design with four replications. Treatments included 3 irrigation regimes (D1: irrigation after 60 mm, D2: irrigation after 120 mm, D3: irrigation after 180 mm evaporation from small tub evaporation) and 5 sunflower cultivars (Azargol, Prograss, Gabur, Hysan 25, and Hysan 36). Results showed that under non-stress and moderate stress, Azargol and Prograss cultivars had the highest rate, in terms of seed filling period, the weight of 1000 grains, stem diameter, and head diameter. Under severe stress, Prograss and Gabur cultivars were remarkable, so that Prograss cultivar had the highest seed filling period, weight of 1000 grains, stem diameter, and Gabur cultivar had the highest number of budding, number of flowering, and stem diameter. In the study of physiological characteristics, results showed that under non-stress and moderate stress chlorophyll a, b, total chlorophyll, and net-photosynthesis in cultivars Progerass and Gabor were significantly increased compared to other cultivars. In severe stress conditions, the Progress and Gabor cultivars in chlorophyll a, b and total chlorophyll content were superior to other cultivars. The results of proline analysis indicated that proline leaf content increased significantly with water stress. Among the cultivars under severe stress conditions, proline leaf content in Progerass and Gabor cultivars was significantly higher than other cultivars. The results of this study showed that Azargol, Gabor, and Progerass cultivars are more tolerant than Hysan 25 and Hysan 36.