Plant growth regulator-mediated modulation of biomass partitioning, root yield and root quality in Ashwagandha (Withania somnifera L. Dunal)

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Ashwagandha (Withania somnifera L. Dunal) is cultivated primarily for its medicinal roots, and improvement in root productivity must be considered together with biomass partitioning and root quality. A field experiment was conducted during the late Kharif season of 2017-18 at the College of Horticulture, Mandsaur, Madhya Pradesh, India, to evaluate the effects of foliar application of indole-3-butyric acid (IBA), 2,3,5-triiodobenzoic acid (TIBA) and chlormequat chloride (CCC) on dry-matter production, root yield, root biochemical quality and economics of Ashwagandha cv. RVA-100. Ten treatments comprising IBA (100, 150 and 200 ppm), TIBA (40, 50 and 60 ppm), CCC (250, 500 and 750 ppm) and water-sprayed control were arranged in a randomized block design with three replications. Sprays were applied at 30, 45 and 75 days after sowing. IBA 100 ppm consistently promoted fresh and dry matter accumulation and produced superior fresh and dry root biomass. It also recorded the highest root harvest index (31.00%) and root yield (461.33 kg ha⁻¹), compared with 269.67 kg ha⁻¹ in the control. Root biochemical responses differed from biomass responses: IBA 200 ppm produced the highest nitrogen (0.67%) and protein (4.10%) concentrations, whereas TIBA 40 ppm produced the highest withanolide content (1.45%). The economic analysis identified IBA 100 ppm as the most profitable treatment in the detailed treatment-wise economic dataset, with the highest net return and benefit:cost ratio. The results demonstrate a clear treatment-dependent trade-off between root biomass and phytochemical concentration. Thus, IBA 100 ppm is the most suitable option when the production objective is root yield and economic return, whereas TIBA 40 ppm may be preferred where enhancement of root withanolide concentration is the primary objective. These findings provide a physiological and production-oriented basis for targeted use of plant growth regulators in Ashwagandha. [1, 2]

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