Evaluation of the sole and integrated application of nano-graphene oxide, zeolite, and chitosan on gas exchanges and silymarin content of milk thistle (Silybum marianum L.) under salinity stress

Identifying environmental factors, plant characteristics, and agronomic activities plays an essential role in medicinal plant production. Milk thistle (Silybum marianum L.) is a well-known medicinal plant with extensive use in diverse liver diseases and is economically a significant crop. This research was conducted to evaluate the effect of the sole and integrated applications of graphene oxide (GO), zeolite, and chitosan as modifying materials on gas exchange and the secondary metabolites of milk thistle under severe salinity stress. Seven sole and integrated combinations of nano-materials comprised of T1, T2, T3, T4, T5, T6, T7, and control (T8, no nano-materials application) and two levels of saline water (12 ds/m) and tap water (control, 0.8 ds/m) were applied to the soil of experimental plots based on a factorial design with three replications. The results showed that the highest photosynthesis rate was obtained with T7 treatment for both water treatments. The highest plant silymarin concentration was obtained from the T6 treatment under both saline and tap water conditions. This treatment increased the silymarin concentration by 15.9% compared to the T8. The highest plant silymarin yield (180 mg per plant) was recorded for the T7 under tap water (control) condition, and 130.3 mg/plant for T6 under salinity stress, respectively. The Transmission Electron Microscope technology indicated that GO at low concentration (0.01%) could be safely used to enhance milk thistle germination and growth under severe salinity stress conditions