Exogenous salicylic acid improves photosynthetic pigments and morphological traits of four medicinal plants in an aeroponic system

Salicylic acid (SA) is a phenolic phytohormone that acts as a key regulator of the signaling network in plants under biotic and abiotic stresses. SA exerts stimulatory effects on various physiological processes to plant growth and development. In this research, valerian, chicory, withania, and purple coneflower plants were transferred into an aeroponic system where the effects of SA were investigated on some plant characteristics under greenhouse conditions. The plants were foliar sprayed with SA (0, 50, 100, and 150 mg l-1) at 20, 40, and 60 days after transplanting (DAT). Results showed that the highest chlorophyll a+b, carotenoid, plant height, root length, root volume, number of leaves per plant, root fresh weight, root dry weight, shoot fresh weight, and shoot dry weight were obtained from 150 mg l-1 SA in all the studied medicinal plants. The results revealed that the exogenous application of SA in the aeroponic system increased the root fresh weight, root dry weight, shoot fresh weight and shoot dry weight of chicory, withania, valerian, and purple coneflower plants. Also, the studied medicinal herbs grew well in the aeroponic system.