Effect of Foliar Application of Salicylic Acid on Reduction of Low Irrigation Impacts in Holy Basil (Ocimum sanctum)

Water deficit is one of the most fundamental problems of agricultural systems throughout the world, which influences both yield and quality of the products. Applying compounds such as salicylic acid (SA) can improve plant resistance against environmental stresses. The present study was conducted to evaluate the impact of drought stress and SA application on quantitative and qualitative traits of holy basil (Ocimum sanctum), based on a factorial experiment in the form of a completely randomized design in three replications. The experimental treatments included drought stress at three levels (100, 70, and 50% FC) and foliar application of salicylic acid at three levels (0, 0.75, and 1.5 mM). Obtained results showed that water deficit caused a decrease in plant growth factors, RWC, and the amount of photosynthetic pigments, while foliar application of salicylic acid increased the above-mentioned parameters. Drought stress and foliar application of salicylic acid increased proline content, total content of phenolic compounds, flavonoid compounds and DPPH free radicals inhibition. In addition, the percentage of essential oils increased under drought stress. Also, plants that were sprayed with salicylic acid, showed a significant increase in essential oil percentage compared to the control. By reducing irrigation water, the percentage of eugenol in essential oil was decreased, but foliar spraying with a high concentration of salicylic acid increased the percentage of this compound. The experimental treatments also had a significant effect on the percentage of 1, 8-cineole and estragole compounds. Therefore, the application of a proper amount of SA can be considered a practical and simple strategy for increasing the quality and quantity of holy basil in arid and semi-arid areas.