Phytochemical responses of camelina to brassinolide and boron foliar spray under irrigation regimes

The high level of boron in dryland and semi-arid soils is an important issue that strongly affects growing and developing crops, especially under drought stress. Meanwhile, brassinosteroid (BR) as a noval stress hormone can improve resistance to abiotic stress in plants. To explore the appropriate foliar application of boron (0.5 and 1 %) and 24-Epi-brassinolide (0.5 and 1 μM) and their combinations on camelina (<i>Camelina sativa</i> L.) under irrigation regimes a field experiment was conducted during 2018-2020 years. Irrigation regime consisted of well irrigation from emergence until the end of the growing season (WI₀), withholding irrigation from flowering to siligue formation (WI₁), and withholding irrigation from siligue formation to harvest (WI₂)]. Our finding revealed that boron had a destructive effect on phytochemical parameters of camelina while application of brassinolide mitigated the boron impacts and improved the parameters. Results showed the highest increase in chlorophyll <i>a</i> (26.8 and 23.8 %) at B_0.5 + BR_0.5 treatments under WI₁ and WI₂ conditions, respectively. Application of BR (0.5 and 1 μM) and low level of B (B_{0.5 %}) combination alleviated drought stress by improving osmolyte accumulation (proline) (5-9% increase), antioxidant enzymes, superoxide dismutase (SOD) (5.35-5.72 % increase), catalase (CAT) capacity (4.10 % increase) and secondary metabolites (total phenol and flavonoid) (6.78-10.26 % and 4.60-5.27 % increase). Further, malondealdehide (MDA) decreased (8.73 %) at BR and B combination and increased with a high level of B (B_1%) application under-withholding irrigation. All of these results confirmed that BR and B synergistically (mainly B_0.5 + BR_0.5 and B_0.5 + BR₁) regulate the phytochemical properties response in the camelina plant to drought stress.