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Abstract
Salicylic acid and ascorbic acid are two naturally occurring plant hormones influencing various physiological and biochemical functions in plants. The present study was aimed to evaluate the effect of salicylic acid (SA) and ascorbic acid (ASC) on essential oil content and compositions of dragonhead (Dracocephalum moldavica L.) under application and non-application of manure. The results showed that application of SA+ ASC significantly increased the essential oil content and essential oil yield compared to control plants. The application of 20 ton/ha farmyard manure increased essential oil content and essential oil yield by 19.2 and 56.8%, respectively. According to the results, essential oil compositions were affected by foliar application of SA and ASC under manure application. The main compositions of dragonhead were geranyl acetate (28.32-47.45%) and geraniol (13.02-25.09%) followed by (Z)-citral (6.6-15.63%), (E)-citral (5.56-15.24%) and neryl acetate (5.1-8.82%). Geranyl acetate was significantly increased with SA and ASC spray under farmyard manure application, so that the highest geranyl acetate percentage was obtained in the plants treated with SA + ASC under 20 ton/ha farmyard manure (47.45%), followed by ASC under 0 ton/ha farmyard manure (41.39%). Geranial as the second main compound in the essential oil was decreased with two latter treatments (46.1 and 38.1%, respectively), compared to control. The results of this study clearly showed that SA and ASC can affect the dragonhead essential oils and its compositions, and they can be used for enhancing or improving the essential oil content and some compositions of dragonhead in an organic agricultural system.