## 1 Introduction  
Among the various abiotic stress factors, water deficit is the one that most affects plant productivity, especially in marginal areas. Safflower, a deep-rooted plant of the Asteraceae family, is tolerant to dry and saline conditions [1]. It has been reported that safflower plants can grow under water deficit without a significant decrease in seed yield [2]. As a drought-tolerant crop, safflower produced a similar seed yield under irrigated and non-irrigated conditions in semi-arid (258.9 mm rainfall per year) and highland (1850 m above sea level) climates in Eastern Anatolia, Turkey [3]. The Crop Water Stress Index (CWSI) is used to quantify the water status of plants. [PERSON] [4] pointed out that leaf temperature is a suitable criterion for the selection of drought-tolerant safflower genotypes. Relative water content (RWC) is an important physiological parameter for measuring the drought stress tolerance of plants [5]. [PERSON] et al. [6], who studied sainfoin (_Onobrychis vicifolia_ Scop.) genotypes under drought stress and non-stressed conditions, reported that water deficit significantly decreased RWC, which affected forage production. [PERSON] et al. [7] showed that seed yield of safflower was greatly reduced under drought stress when 100, 75, 50, 25 and 0 per cent of maximum evapotranspiration was restored. The results of a study showed that wheat genotypes with lower grain yield under severe water deficit conditions had lower water use efficiency (WUE), stomatal conductance and transpiration than others [8]. Evaluation of the growth and performance of durum wheat and triticale in the Mediterranean climate showed that triticale with higher stomatal conductance and transpiration efficiency had higher water and radiation efficiency in the dry season [9]. Osmotic adaptation (Oadj) is considered an important physiological mechanism of adaptation to water deficit in many crops [10]. It appears that Oadj may be an important mechanism of drought tolerance in plants such as safflower under drought conditions. [PERSON] et al. [11] studied Oadj in chickpea lines and progeny from their crosses under late drought conditions and found that OA does not contribute to seed yield. They concluded that Oadj is not a suitable trait for the selection of water deficit-tolerant genotypes of chickpea. [PERSON] et al. [12] found that the highest water use efficiency in safflower with mean values of 3.04 and 1.23 kg ha\({}^{-1}\) mm\({}^{-1}\) was achieved with three and one supplemental irrigation, respectively. The additional irrigation also had a significant influence on grain yield. Thus, a grain yield of 392 kg ha\({}^{-1}\) was obtained with one irrigation and the yield was 48% higher with two irrigations than with a single irrigation, while a grain yield of 1258 kg ha\({}^{-1}\) was obtained with three irrigations, 220% higher than with a single irrigation. The results of evaluation of safflower cultivars under water deficit stress at different reproductive stages showed that drought during flowering and bud formation resulted in a decrease in water use efficiency by 28.9 and 18.3 percent, respectively [13]. [PERSON] et al. [14] reported that WUE can be used as an indirect trait for the selection of water deficit-tolerant genotypes of oilseed rape (_Brassic napus_ L.). The results of the study of safflower genotypes under pre-seasonal and seasonal irrigation showed that the differences between genotypes in WUE were insignificant and small [15]. [PERSON] and [PERSON] [16] pointed out that all generative subphases of safflower respond to water deficit. [PERSON] et al. [17] reported that moderate and severe drought stress significantly reduced the performance of safflower. The results of the evaluation of the six safflower lines under normal and drought conditions showed significant differences in leaf chlorophyll content, RWC, water potential and seed yield.