Title : Optimizing moisture stress and salicylic acid application to enhance root yield and bioactive compounds in ashwagandha (Withania somnifera)
Abstract:
Ashwagandha (Withania somnifera), a widely used medicinal herb in the Solanaceae family, is known for its anti-inflammatory, anti-aging, immunomodulatory, and anticancer properties. Its root is the key component in herbal formulations, making root yield and bioactive compound content critical for medicinal applications. This study investigates the effects of moisture stress and salicylic acid (SA) application on Ashwagandha’s growth, yield, and secondary metabolite production under controlled conditions. A polyhouse experiment was conducted in the WL2B climate zone of Sri Lanka. Two independent trials were performed: (1) assessing four soil moisture levels (50%, 60%, 80%, and 100% of field capacity [FC]) combined with SA foliar sprays at concentrations of 10 mM, 1 mM, 0.1 mM, and a control (no SA), and (2) evaluating seven moisture stress levels (50–100% FC [control], 45–50% FC, 40–45% FC, 35–40% FC, 30–35% FC, 25–30% FC, and 20–25% FC). Each treatment was replicated three times, with individual plants grown in sand-filled pots. Growth parameters such as plant height, number of leaves, SPAD value, root dry matter, polyphenol content, flavonoid content, and DPPH radical scavenging activity were measured. Results indicated that the highest root dry weight (7.62 g) and total polyphenol content (3.78 GAE mg/g d.w.b) were obtained under 50% FC with 1 mM SA, increasing root dry weight and total polyphenol content by 2.7 and 12.49 folds, respectively, compared to the control (100% FC without SA). In the second experiment, the highest shoot growth (plant height, number of leaves, and SPAD value) was observed in plants at 50–100% FC. However, the highest root dry matter (0.59 ± 0.09 g), total polyphenol content (5.75 ± 0.02 GAE mg/g d.w.b), flavonoid content (2.90 ± 0.03 mg CEQ/g d.w.b), and DPPH radical scavenging activity (80.69% ± 0.67) were recorded under 35–40% FC. These findings suggest that moderate drought stress (35–40% FC) enhances root yield and bioactive compound accumulation in Ashwagandha.
Recommendations:
A moisture stress level of 35–40% FC is recommended to maximize root biomass and secondary metabolite production, improving the medicinal quality of Ashwagandha. Additionally, foliar application of 1 mM SA under 50% FC significantly enhances root dry weight and polyphenol accumulation, making it an effective strategy for increasing Ashwagandha’s pharmaceutical potential. While controlled drought stress can stimulate secondary metabolite synthesis, extreme stress (below 35% FC) may negatively affect plant health.
Future Perspectives:
Further research should focus on the genetic and biochemical mechanisms underlying Ashwagandha’s response to drought stress and SA application. Understanding these pathways can help optimize sustainable cultivation strategies and enhance the plant’s medicinal value. Given the growing global demand for high-quality medicinal herbs, integrating moisture stress management and SA applications can significantly improve Ashwagandha cultivation, contributing to sustainable agriculture and the herbal medicine industry.
