Effects of salicylic acid and cycocel on percentage and yield of essential oil and physiological characteristics on Moldavian balm (Dracocephalum moldavica L.) under drought stress conditions

Introduction Drought is one of the most important environmental stresses that affects the morphology, physiology and biochemistry of the plant and it has a major impact on agricultural production. The Moldavian balm is herbaceous that originated in middle Asia and about 66 compound are identified in this plant. Application of growth regulator lead to increases of plant resistance against biotic and abiotic stress and is involved as a strategy to prevents adverse effects of environmental stress. According to semi-sensitivity of dragonhead plant to drought condition, its medicinal importance as well as, its industrial widespread use, this study was conducted to evaluate dragonhead essential oil yield and its compound under drought condition and also, to evaluate physiological aspect of drought resistance. Material and methods In order to investigate the effects of salicylic acid and cycocel on the gas exchange on Moldavian balm in drought stress condition research was conducted in the spring of 2014 and 2015 at research farm of agricultural college, Zanjan University. The experiment was laid out in split plot with two factors of moisture levels and growth regulators in a randomized complete block design with four replications. The main factor is the moisture levels at two levels without stress (Complete irrigation until the end of the growth period), drought stress (Complete irrigation before start flowering and discontinuation of irrigation until the end of the growth period). Sub-substrate of different levels of salicylic acid (800 and 1600 μm), cycocel (600 and 1200 μm), and control (dissolve with distilled water), which applied for a single application before start flowering. Findings The results of two-year combined analysis of variance showed that the interactions of the sampling stage in the year in moisture for leaf relative water content, canopy temperature, essential oil percent, essential oil yield, plant fresh weight and plant dry weight was significant at the 1% probability level. Mean interactions of growth regulator in during sampling stage showed the salicylic acid treatment (800 μM) at the end of flowering stage (H3B1) had the highest percentage of essential oil (0.37) and the lowest percentage of essential oil is related to the 600 micro molar (0.16) cycocel treatment at the flowering stage (H1B2). Conclusion  The percentage of essential oil in the start flowering stages, flowering and flowering ends is increasing, so that the highest percentage of essential oil is associated with the flowering ends stage. Under stress conditions, the essential oil yield is reduced. Cycocel treatments 1200 micro molar it was caused by increased root growth and increased water absorption from the depths of the soil the plant has more essential oil than other treatments. In drought stress conditions, essential oil yield decreased and essential oil percentage increased. Also, by applying drought stress, the water status of the plant changes significantly and the relative water content of the leaves decreases. According to the results of the experiment, it can be concluded that drought stress reduced the yield and essential oil percentage of the Moldavian balm.The use of salicylic acid in conditions of drought stress compared to cycocel increases the yield and essential oil percentage.