Foliar salicylic acid spraying effect’ on growth, seed oil content, and physiology of drought-stressed Silybum marianum L. plant

Abstract

Water deficit is one of the most sever worldwide problems of agricultural systems, which influences both yield and quality. Applying compositions like salicylic acid (SA) can improve plant resistance against environmental stresses. The present study was conducted to evaluate the impact of irrigation intervals and SA application on plant growth, osmotic parameters, oil yield, and oil composition of milk thistle. A completely randomized design was applied with a factorial arrangement of two factors: irrigation intervals as the first factor, including 5 days (control), 10 days (D1), 15 days (D2), 20 days (D3) and SA application as the second factor, including 0, 0.5 and 1 mM. From the obtained results, it was clear that water deficit damaged plant growth, including relative water content (RWC), seed yield, and oil content. Results show that spraying 0.5 mM SA partially increased plant growth and seed yield parameters under control condition. Under drought stress conditions, spraying 1 mM of SA had more significant effects on higher seed yield and oil content, compared to 0.5 Mm. Drought stress increased proline content, total soluble carbohydrates (TSC), sucrose, total phenolic compounds (TPC), and DPPH free radical scavenging, while applying 1 mM of SA increased these parameters in both well-watered and water deficit conditions. In addition, the production of linolenic acid, palmitic acid, and stearic acid enhanced under drought stress, while linoleic acid and total soluble proteins (TSP) dropped by increasing drought intensity. Applying 1 mM of SA increased all these parameters more effectively than other SA treatments. According to our results, we suggest that SA can play an essential role as a regulator for improving osmotic adjustment, RWC, and yield of milk thistle plants under drought stress conditions. Therefore, the application of a proper amount of SA can be considered as a practical and straightforward strategy for increasing seed oil quality and seed yield, for both industrial and edible purposes, in arid and semi-arid areas.