Salicylic Acid Foliar Spray Enhanced <i>Silybum marianum</i> Growth and Yield, as Well as Its Chemical Constituents and <i>Chalcone Synthase</i> Gene Activity

Silymarin, a secondary metabolite found mainly in the <i>Silybum marianum</i> L. fruits, has been associated with the hepatoprotective activity of the plant. Among various elicitors, salicylic acid, a “Generally Regarded As Safe” compound recognized by the Food and Drug Administration, is one of those being used in the induction and enhancement of valuable plant secondary metabolite production in various plant species. In this study, two concentrations (10⁻⁴ and 10⁻³ molar) of salicylic acid have been applied to the <i>S. marianum</i> plants as foliar spray to investigate their effects on plant growth and yield, as well as the production of its bioactive compound, silymarin. Our results indicated that both concentrations of salicylic acid increased the plant height, the number of branches, leaves, and capitula, as well as the dried weight of roots, aerial parts, and fruits. The enhancement effects in plant growth and yield were accompanied by an increase in photosynthetic pigments such as chlorophyll-a, b, and carotenoids as well as element contents such as nitrogen, phosphorus, and potassium. The potential of salicylic acid as an elicitor for the enhancement of secondary metabolites in <i>S. marianum</i> was supported by the increase in silymarin’s major components, silybin (A + B), in the salicylic acid-treated plants. Concomitant expressions of <i>CHS</i><i>1</i>, <i>2</i>, and <i>3</i> genes that have been associated with the production of silymarin in <i>S. marianum</i> were also observed in the salicylic acid-treated plants. A lower concentration (10⁻⁴ M) of salicylic acid was found to be a better elicitor as compared with the 10⁻³ M salicylic acid. An increase of 3.4 times in capitula number and fruit dried weight as well as 2.6 times in silybin (A + B) contents were observed in plants sprayed with 10⁻⁴ M of salicylic acid as compared with the control.