Effects of salicylic acid application on yield and essential oil content of Moldavian balm (Dracocephalum moldavica L.) under drought stress conditions

Moldavian balm (Dracocephalum moldavica L.), belonging to the Lamiaceae family, is an annual and aromatic plant, which is used in traditional and modern medicine in the treatment of gastrointestinal and cardiovascular disorders. In order to evaluate the effect of salicylic acid on yield and essential oil of Moldavian balm under drought stress conditions, a field experiment was conducted as a split plot based on randomized complete blocks design with three replications at the Department of Natural Resources and Watershed of Piranshahr City in 2012. The main factor was irrigation at three levels (40, 80 and 120 mm evaporation from pan), and the sub factor was plant spraying with salicylic acid at three levels (0, 0.5 and 1 mM). Results showed that the effect of drought stress on dry yield, thousand seed weight, harvest index of flowering stem, and essential oil yield was significant. Similar results were obtained for the effect of plant spraying with salicylic acid on dry weight and essential oil yield. It should be noted that dry yield and essential oils yield were most affected by drought stress. In addition, the highest values of thousand seed weight and harvest index of flowering stem was related to the irrigation treatment of 120 mm evaporation. The present study results also showed that the interaction effect of two factors studied on essential oil percentage and essential oil harvest index was significant. In this regard, the maximum amount of essential oil and essential oil harvest index belonged to application of 1 mM salicylic acid in irrigation treatment of 120 mm evaporation from pan.