Planting date affected biochemical characteristics, assimilate remobilization, yield components and yield of safflower cultivars under water stress

Adjusting the planting date is a low-cost and easy way to overcome the effects of water stress. A two-year field study was conducted to consider the effect of planting dates on biochemical and physiological characteristics and yield of safflower under water stress. Treatments consisted of irrigation regime (normal irrigation, and irrigation cut-off at flowering and seed filling stages), planting date (6 and 26 December and 15 January) and safflower cultivar (Goldasht and Isfahan). Irrigation cut-off at flowering and seed filling decreased total chlorophyll between 7.5 to 28.4 % while carotenoid content, catalase and peroxidase reached the highest amount on 6 and 26 Dec. Under irrigation cut-off at flowering, the relative water content (RWC) of Goldasht on 26 Dec planting date was more than Isfahan between 10.8 to 11.7%. Although irrigation cut-off at flowering increased the canopy temperature, Goldasht on 26 Dec had the lowest canopy temperature. In Goldasht on 26 Dec planting date, the seed yield decreased between 21.4 to 31.0% under irrigation cut-off which was less than the other planting dates. The dry matter remobilization and remobilization efficiency due to higher mean temperatures and evaporation in the first year was more than the second year. A positive relationship was observed between seed yield with total chlorophyll, RWC, number of seed per capitula, remobilization efficiency and water use efficiency. Overall, 26 Dec planting date was the optimum planting date especially in Goldasht, but a late planting date could not mitigate the negative effect of water stress.