Altered biomass allocation and quality improvement in roots of Indian ginseng Withania somnifera Dunal. Linn. through physiological interventions

Ashwagandha (W. somnifera Dunal. Linn.), known as Indian ginseng, contains three major bioactive compounds, withaferin-A (WA), 12-deoxywithastramonolide (WO) and withanoloide A (WD). In a field experiment, the impacts of foliar application of growth retardants/promoters was assessed with respect to biomass allocation pattern and major withanoloide content at different phenological stages in W. somnifera. Biomass accumulation pattern showed that foliar application of 500 mg l−1ethrel at 50, 65, 85, 105, and 120 days after sowing (DAS) restricted phenological progression and reduced berry weight by 61% as comparted to the control at 160 DAS. 500 mg l−1 succinic acid foliar application resulted in maximum plant height (56.4 cm), maximum dry stem weight (DWS) and dry root weight (DRW) whereas 500 mg l−1 ethrel had resulted in minimum plant height and DRW at 180 DAS. During last 50 days of crop growth, the accumulation pattern drastically changed with more than 60% of the biomass allotment to the reproductive part, the berries. The WD in roots ranged between 0.325 mg g−1and 0.342 mg g−1 during all growth stages. WA content decreased with increase in progression of crop growth and reached the lowest at 180–190 DAS. In a pot experiment, ethrel application up regulated DWF-5 by 2.44, SQE by 3.79 and CYP450s by 1.17 log2fold in roots 8 h after treatment and succinic acid had up regulated the expression of all these genes by nearly 3 log2fold change. This is in accordance with the withanoloide accumulation pattern in field condition under foliar application of these molecules.