Chemical manipulation of source and sink dynamics improves significantly the root biomass and the withanolides yield in Withania somnifera

Roots are the main economic part of Withania somnifera having high commercial value in the pharmaceutical industry. Since W. somnifera has the indeterminant type of growth habit, it exhibits a continuous berry formation which ultimately reduces the root yield. The present study was undertaken to determine the effect of altered source - sink relationship by regulating the sink availability to increase the root yields. Maleic hydrazide (MH @ 200, 500 and 1000 μmol mol−1) and Gibberellic acid (GA @ 500 and 1000 μmol mol−1) were used as chemical gametocide for inducing male sterility while mechanical deflowering was used to prevent the berry formation. In all three approaches, the root biomass and withanolides content, in general, were significantly increased. The dry matter partitioning pattern showed that only 6% of total biomass was accumulated in the roots whereas 37% accululated in the shoot and a significant amount i.e., 57% was partitioned to the berries under control condition. An application of MH and GA and the mechanical deflowering treatment, however, changed this pattern in favour of the roots. As much as 26% of the total biomass was partitioned to the roots under the MH treatments. Whereas, GA (500 μmol mol−1) and mechanical deflowering treatment increased the root biomass by 75 and more than 300% respectively. More than 200% increase in withaferin A and ∼100% increase in withanolide A content was observed in leaves under the GA (500 μmol mol−1) treatment. Mechanical deflowering treatment was also equally efficient as GA in increasing the withanolides both in the leaves and the roots. The photosynthetic traits, total sugars and starch content, and sugar metabolizing enzyme analysis showed that modification in source-sink relationship through inhibited berry formation triggers a higher partitioning of carbon assimilates from source to the roots and thus improves significantly the root biomass and the withanolide yields in W. somnifera. The same was validated through the radiotracer studies involving 14C.