Abstract
This research was conducted as a combined analysis with four replications in two years (2018 ‒ 2019). Treatments were irrigation up to 90%, 50%, and 20% field capacity (as normal irrigation, moderate and severe water deficit stresses, respectively) and foliar application of natural regulators (untreated as control, salicylic acid, spermidine, and methanol). Increasing water deficit stress was led to a significant increase in essential oil percentage and proline content and a significant decrease in yield parameters and seed yield. Most of the traits (except the percentage of essential oil) were affected by natural growth regulators. The highest seed yield (1,127.59 kg/ha), plant biomass (5,426.92 kg/ha), essential oil yield (22.67 kg/ha), and proline content (29.34 μmol/g fresh weight) were obtained in methanol treated plants under normal irrigation. However, the highest amount of these traits under moderate and severe water deficit was recorded for salicylic acid-treated plants. Therefore, foliar spray of methanol was a useful treatment for non-stress conditions, but, application of salicylic acid was the superior treatment for reducing the negative effects of water deficit stress on Foeniculum vulgare.