Grain Yield and Active Substances of Milk Thistle as Affected by Soil Salinity

The ripe seeds of milk thistle ( Silybum marianum L. Gaertn) contain active substances of flavonoides that are important in the pharmaceutical industry. Evidence showed that stress conditions such as salinity can affect growth and development of plants, including active substances of some medicinal plants. Silymarin and silybin are important active materials of milk thistle whose concentrations correspond to some degree of plant stress. To test for this relationship, a pot experiment was conducted using a completely randomized design with seven level of salinities (0.35, 1, 3, 6, 9, 12, and 15 dS/m) for two genotypes, Ahwaz wild type and cultivated German origin (Royston). At the harvest, the results have showed that both genotypes grow satisfactorily and had a normal size in soils up to salinity of 9 dS/m, compared to the control plants. However, growth parameters such as plant height, number of leaves per plant, number of capitula per plant, main shoot capitulum's diameter, and seed yield and yield components per plant was reduced with salinity greater than 9 dS/m in both genotypes. However, concentrations of active substances (silymarin and silybin) in seeds significantly increased compared to the control plants. Results from the high-performance liquid chromatography ( HPLC) analysis indicated that the amount of silybin was approximately four times greater in plants cultivated under a salinity of 15 dS/m than in the plants grown under nonsaline conditions. Our results suggested that both types of milk thistle survive under salinity as high as 15 dS/m levels and produced seeds with rich in active substances.