Effects of potassium and brassinosteroid on some morphophysiological characteristics and essential oil yield of Echinacea purpurea (L.) Moench under different regimens of water availability Availability

The aim of this study was to investigate the effects of soil application of potassium fertilizer and foliar application of brasinosteroid on morphophysiological characteristics and essential oil yield of medicinal plant purple coneflower (Echinacea purpurea (L.) Moench) in response to water availability. Treatments consisted of three levels of water availability (irrigation at 90% (control), 60%, and 30% of field capacity (FC)) in main plots and four amounts of potassium fertilizer (no potassium application (control), 50, 100, and 150 kg K2O ha-1) as well as the foliar application of three brassinosteroid concentrations (distilled water (control), 0.1, and 1 μM) in subplots. Results showed that the highest mean plant height (67.8 cm), number of leaves plant-1(151), number of flowers plant-1 (18.1), flower dry weight (151.9 g plant-1) and aerial parts dry weight (508.6 g plant-1) were obtained in the second year of the experiment under 150 kg ha-1 potassium and normal irrigation treatments. The highest percentage of essential oil (76) was obtained under irrigation at 60% of FC, 150 kg ha-1 potassium, and 1 µM brassinosteroid treatments. In the second year, the maximum amount of essential oil plant-1 (0.67 g) was related to 150 kg ha-1 potassium and 1 μm brassinosteroid treatments. In general, the results of this study showed that irrigation at 60% of FC together with 150 kg ha-1 potassium and 1 μM of brassinosteroid could reduce the effects of drought stress, increase the amount of essential oil plant-1 and improve some morphophysiological characteristics in purple coneflower.