Changes in growth and essential oil content of dill (Anethum graveolens) organs under drought stress in response to salicylic acid

Some of the harmful impacts of water shortage on crop performance may be alleviated by growth regulators such as salicylic acid. So, an experiment was arranged as a split-plot design based on randomized complete blocks in three replicates to assess changes in essential oil content of dill (Anethum graveolens L.) organs in response to water availability (water supply after 70, 100, 130, 160 mm evaporation as normal watering and mild, moderate and severe stresses, respectively), and salicylic acid (SA) levels (water spray and 0.6, 1.2 mM SA). Irrigation levels and salicylic acid treatments were assigned to the main and sub-plots, respectively. The results showed that chlorophyll a and especially chlorophyll b decreased with increasing drought stress. The ground green cover and plant organ masses (leaves and stem, flowers, and seeds) were only decreased under severe water deficit. Essential oil percentage of dill organs increased with increasing water deficit up to moderate stress, but thereafter it was decreased as water deficit severed. The highest essential oil yield of the vegetative parts and flowers was also produced in moderately stressed plants, but the greatest essential oil yield of seeds was recorded under mild water deficit. Exogenous salicylic acid enhanced the essential oil percentage of all dill organs, especially under moderate water limitation. The essential oil yield of dill organs was also increased by the salicylic acid treatment. The application of 1.2 mM salicylic acid was more effective in improving essential oil production of dill.