Safflower’s (Carthamus tinctorius L.) physio-biochemical mechanisms to improve its drought tolerance

Drought is a main stressor affecting plant production worldwide. Safflower (Carthamus tinctorius L.) is known to exploit biochemical strategies to tolerate drought stress. However, the little so far known about these strategies does not guarantee safflower yield stability in future. To fill the gap, changes in the biochemical traits and antioxidant activities of safflower were monitored using 100 genotypes under the two non-stress and drought-stress field conditions in two subsequent years (2017 and 2018). While drought stress was observed to give rise to reversible increases in total phenolics (TPC), total flavonoids (TFD), total flavonols (TFL), total anthocyanin (Ant), proline, malondialdehyde (MDA), and antioxidant activity, it decreased total chlorophyll (ChlT) and total carotenoid (Car) contents in safflower. Under drought stress, the highest values for TPC (21.55 16.07 mg GAEg⁻¹ fresh weight [FW]), Car (0.08 mg g⁻¹ FW), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) activity (98%) were measured in G₁₆, averaged over the two study years. Also the highest values for TFD (5.17 mg QEg⁻¹ FW), TFL (1.99 mg QEg⁻¹ FW), Ant (234.1 µmol g⁻¹ FW), ChlT (0.67 mg g⁻¹ FW), and proline (851 μmol g ⁻¹ FW) were recorded for G₈₀, G₆₀, G₂₃, G₆₂, and G₃₃. The least MDA content (2.8 µmol g⁻¹ FW) was denoted to G₉₁ under drought stress. The results of both principal component and correlation analyses demonstrated the effective role of total flavonoids in safflower drought tolerance. The high genetic variance was seen to result in the high heritability of biochemical traits under drought stress, thereby improving drought tolerance in safflower cultivated in drought prone regions. The significant genetic variations in all the biochemical traits indicated that these traits, especially TPC and TFD, could be used as screening criteria for genotypic selection in arid climates.