Safflower ( Carthamus tinctorius L.) seed germination, seedling growth and biochemical properties affected by drought stress, genotype and 24-epibrassinosteroid

Finding methods, which may alleviate drought stress on the growth and biochemical properties of safflower (Carthamus tinctorius L.), as one of the important medicinal plants, is of significance. The objective was to alleviate drought stress on seed germination, seedling growth, and biochemical properties of different genotypes of safflower using 24-epibrassinosteroid (EBR). The experiments, conducted in the greenhouse in 2014 and 2015, were factorial on the basis of a complete randomized block design with three replicates. Drought stress (85 (S1), 65 (S2) and 45% (S3) of field capacity), genotype (Goldasht, Faraman and Sina), and the foliar application of 24-epibrassinosteroid (EBR) (0 and 10−7 M) were tested. Seed germination indices, seedling growth and biochemical properties were determined. The results indicated the significant effects of drought stress on the measured parameters including seed germination, which was the most sensitive stage. The use of EBR significantly increased seed germination and seedling growth, nutrient uptake and grain protein and oil contents, at different levels of stress. EBR significantly enhanced grain N (7.3%) and P (0.5%) uptake, as well as protein percentage (38.7%), even at the highest level of stress (S3), to the levels which were comparable with S1 and S2. The use of EBR may improve seed germination and the growth of safflower seedlings under drought stress conditions by affecting the physiological properties, mainly related to the mechanisms of protein production.