مشخصات پژوهش

Milk Thistle (Silybum marianum L.) is one of the important ancient medicinal plants that have been used to treat liver disease, bile-related diseases and poisoned individuals by poisonous mushrooms. As an important medicinal plant in some industries such as pharmaceutical industry, the antioxidant capacity of milk thistle in conferring drought stress, as well as physiological and yield-related traits were studied. The experiment was a split plot based on randomized complete block design with three replications. The main plots included different irrigation levels (including 80, 60, 40 and 20 percent of the available soil water content) and ecotypes of Tehran and Hamedan were considered as sub-plots. Results indicated that the grain yield of Tehran ecotype was reduced 3.3%, 19.5% and 52.3% under mild, moderate and sever stress compared to optimum conditions, respectively. The grain yield of Hamedan ecotype was reduced 7.8%, 42.3% and 73.2%, respectively. Essential oil yield of Tehran and Hamedan ecotypes decreased by 22.1% and 63% in severe drought stress conditions, respectively. Tehran ecotype had higher levels of carbohydrate and proline than those of Hamedan under stress conditions. This property caused the Tehran ecotype to have more relative water content and lower slope change of grain yield and essential oil yield as compared with Hamedan. Drought stress increased the percentage of essential oil in both ecotypes and the essential oil of Tehran contained more antioxidant. In general, under mild stress conditions, the highest essential oil yield was obtained due to an increase in essential oil content and no significant reduction in grain yield. Thus, it seems that the application of mild controlled stress improves the quality of milk thistle without affecting its quantitative performance.