Exogenously used boron and 24-epibrassinolide improved oil quality and mitigate late-season water deficit stress in camelina

The high oil content and quality of camelina [Camelina sativa (L.) Crantz] seed oil for various uses, including human nutrition and industry, has encouraged many countries to increase the cultivation of this oilseed crop. Due to the coincidence of initial irrigations of summer crops with the final stages of camelina growth, production of this crop in arid and semi-arid regions depends on tolerance to the late-season water deficit stress. Therefore this two years field experiment focused on boron (B) and 24-epibrassinolide (EBL) foliar spray effect on seed yield, oil content, oil yield and fatty acids profile (FAs) of camelina in a semi-arid area (Iran) during 2018−19 and 2019−20 growing season. Experimental treatments were arranged in a split-plot design based on randomized complete blocks with three replicates. Irrigation regimes based on withholding irrigation (WI): [full irrigation (FI) at 50 % of available soil water (ASW); withholding irrigation with 20 % of ASW from full flowering to silicle formation (WI₁); withholding irrigation with 20 % of ASW from silicle formation to harvesting (WI₂)] were considered as the main plots and ten levels of foliar spray (FS) consisted of control (non foliar spray), distilled water, B (0.5 and 1%) and EBL (0.5 and 1 μM) and their concomitant use (B 0.5 % + EBL ₀.₅μₘ, B 0.5 % + EBL ₁μₘ, B ₁% + EBL ₀.₅μₘ, and B ₁% + EBL ₁μₘ) were randomized to the subplot units. Seed and oil yield decreased by 6.7–8.4 % and 10–12 %, respectively in response to the water deficit during the flowering and silicle formation stages. The negative effect of drought stress on the quality of camelina oil was recorded as 3.3–5.3 % increment in erucic acid and significant decrease in the unsaturated fatty acids (UFAs) content, oleic acid (by 4.6–8.5 %), linoleic acid (by 3.5 %), linolenic acid (by 2.5 %) and 1.2–2.8 % for monounsaturated fatty acids (ΣMUFAs) content compared with the control treatment. While foliar spary of B and EBL increased oil content by ranged from 2 to 4% under-withholding irrigation treatments. Also ecosanoic acid and polyunsaturated fatty acids (ΣPUFAs) content significantly increased under combined application of B₀.₅ + EBL (₀.₅ ₐₙd ₁).