Research related to plant responses to combined stresses is very limited, especially in medicinal plants. Present investigation was conducted in order to evaluate the effects of drought and UV-B stress on physiological performance and chemical properties of major Iranian medicinal species of Bunium persicum. A factorial plan based on a randomized complete block design was performed with two irrigation levels [irrigation after 60 (control) and 150 mm (drought stress) evaporation from evaporation pan] and three UV-B treatments [no UV (control), 1 and 2 hr radiation] in three replications. Results showed that plants under normal water condition and 2 hr UV-B radiation produced a higher seed yield. Yield components were generally higher in normal water condition and 1 hr UV-B treatments, except for some parameters, including seed size. Plants which grown under UV radiation had higher content of essential oil (EO) compared with the ones that did not receive UV treatments. Contrary with the yield components, qualitative properties of EO were affected by the levels of applied treatments and drought stress, and the 2 hr UV-B treatments highly improved antioxidative properties of EO. 22 -diphenyl 1-picrylhydrazyl radical (DPPH) scavenging activity, hydrogen peroxide scavenging activity, Fe reducing power and phenol content were enhanced by high UV-B radiation level and drought conditions. In general, some alleviative effects between drought and UV-B were observed in regards to yield and yield components of B. persicum, although they were not very considerable. The interaction of applied treatments was more obvious in antioxidative activities of essential oil.

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