Plant Growth Promoters (PGPs) Alleviate Salt Stress, Enhance Physiological Parameters, Secondary Metabolites and Silymarin Content in Milk Thistle

The objective of this research is to explore the impact of plant growth promoters on enhancing the growth, yield, antioxidants, reactive oxygen species and phytochemical production (including flavonoids, lignin, and secondary metabolites) of Milk thistle (Silybum marianum L. Gaert.) under salt stress conditions. This study aims to fill the gap in knowledge regarding the potential of these growth promoters in improving the salt tolerance potential of Milk thistle when exposed to a saline environment. A pot study was conducted during the years 2017 and 2018 to determine the effect of plant growth promoters (such as thiourea, moringa leaf extract, and ascorbic acid) on yield qualities, secondary metabolites, and the silymarin content of milk thistle under salt stress. Data analyzed for silymarin content (239.99%), phenylalanine ammonia-lyase activity (199%), and flavonoids (42.17%) revealed a strong relationship with the soil-supplied plant growth stimulants, particularly ascorbic acid. Furthermore, the increasing trend of yield characteristics, silymarin accumulation, and antioxidant activities was noted in the Quetta ecotype, followed by Faisalabad and Gujranwala. Given the importance of silymarin to the medical sector and its involvement in the treatment of various serious illnesses, it is suggested that the Quetta ecotype be promoted for cultivation with soil supplementation of plant growth regulators to obtain a higher silymarin yield. In conclusion, plant growth promoters, regardless of ecotypic changes, efficiently increase the secondary metabolites and silymarin content under salt stress.