## 4 Discussion  
Water deficit stress during the reproductive phase of safflower genotypes led to a significant reduction in the studied physiological traits, including RWC, gs, Oadj, WP and WUEa, and to an increase in CWSI (Tables 3 and 4). The values of the mentioned traits among safflower genotypes were significantly different (Tables 3 and 4). [PERSON] and [PERSON] [33] described that safflower germplasm contains different genetic material to improve seed yield, earliness and drought-tolerant varieties. Stomatal conductance decreased under drought and heat stress during the flowering and seed-filling stages. This led to a reduction in mesophyll conductance in oilseed rape [34]. As a result, the lower carbon uptake led to a lower seed yield in oilseed rape genotypes. The results of a study on safflower under water deficit stress at different growth stages showed that water supply at  
Figure 1: The regression relationships between the seed yield (kg/ha) of safflower genotypes as a linear or non-linear function with water stress index (**a**), relative water content (**b**), stomatal conductance (**c**), osmotic adjustment (**d**), water potential (**e**) and water use efficiency (**f**) under drought stress and non-stress conditions. the flowering and capitulum development stages improved the water use efficiency and seed yield of safflower [35]. [PERSON] et al. [36] studied maize crops under normal and dry stress conditions and found a significant correlation between the plant water stress index and stomatal conductance (R\({}^{2}\) = 0.90). The results of measuring differences in canopy and air temperature of winter rye genotypes under normal and water deficit conditions showed that the mentioned index can detect differences in water deficit stress tolerance more accurately than the determination of the grain yield of rye [37]. The correlations between the physiological traits were positive (negative for CWSI) and significant (Table 5). They also showed positive (negative for CWSI) and significant correlations with seed yield (Table 5) (except for Oadj). The regression relationships between seed yield of safflower genotypes and physiological traits showed that CWSI, WP and WUEa had a strong relationship with seed yield and impressively high R\({}^{2}\) coefficients under both normal and water deficit stress during flowering and seed filling stages. The regression analysis equations showed that more than 80 percent of the total variation in seed yield could be independently explained by CWSI, WP or WUEa under stress and non-stress conditions. These parameters can be used more reliably to predict seed yield under stress and non-stress conditions (Figure 1). It appears that a reduction in water availability under drought conditions through a decrease in water potential and stomatal conductance of leaves and an increase in leaf temperature in safflower genotypes reduces seed yield by reducing photosynthesis. In conclusion, water stress index, water potential and agronomic water use efficiency are able to select high-yielding and drought-tolerant safflower genotypes for the late season. Most of the world's safflower production comes from marginal and arid areas. Therefore, water deficit stress, especially during the flowering and seed-filling phase, is the main limiting factor. Therefore, accurate, fast and cost-effective methods are needed to select drought-tolerant and high-yielding safflower genotypes. The cultivation of suitable safflower genotypes on marginal soils represents a valuable opportunity to prevent soil erosion and secure an economic income for farmers in threatened areas. The results of a study show that leaf temperature is a suitable criterion for the selection of drought-tolerant safflower genotypes [4]. The study of safflower genotypes under pre-season and in-season irrigation conditions showed that the differences between genotypes were insignificant and small for WUE [15].