Growth and polyphenol content of Ashwagandha (Withania somnifera L. Dunal) under combined drought stress and salicylic acid treatment

Ashwagandha is a medicinal herb that has very high demand in the global market. Root is the main part harvested from this plant because of its rejuvenating properties. This study investigated the effects of drought stress and salicylic acid on the growth yield and polyphenol content of Ashwagandha. A polyhouse experiment was conducted where Ashwagandha plants were grown under four levels of soil moisture that included 50%, 60%, 80%, and 100% of field capacity (FC) and four Salicylic acid (SA) levels as control, 0.1 mM, 1 mM and 10 mM was applied as a foliar spray as treatments to induce the secondary metabolite production. Plant height, number of leaves, number of fruits, number of fallen leaves, SPAD value and leaf area, root dry matter content, free proline content and total polyphenol content were measured. The highest root dry matter content (7.62 g) and total polyphenol content (3.78 GAE mg/g d.w.b) were reported with the interaction effect of 50% of FC and combined with 1 mM SA application. Under the combined effect of 50% of FC and 1 mM SA the root dry matter content, free proline content and total polyphenol content were increased by 2.7, 2.13 and 12.49 folds respectively compared to control (100% FC and without SA). These findings suggest that a drought stress level of 50% field capacity combined with a 1 mM SA foliar spray can significantly enhance the root yield and polyphenol content of Ashwagandha.