Micronutrient-mediated modulation of biomass, essential oil yield and composition in aromatic marigold from the western Himalayas

The present study investigates the effect of foliar application of zinc (Zn) and boron (B), on growth, essential oil (EO) yield, and composition of Tagetes minuta. Foliar sprays of Zn and B were applied individually and in combination at 100, 200 and 300 mg L−l. Application of Zn + B at 200 mg L−l significantly improved growth parameters, with EO content ranging from 0.61 - 0.76% and biomass yield from 40.7 – 46.4 q ha−1. Application of Zn + B @200 mg L−l significantly enhanced EO content and biomass yield by 25.3 and 14.1% in contrast to control, respectively. Major EO constituents included (Z)-β-ocimene (27.7–40.2%), (E)-ocimenone (15.7–20.4%), dihydrotagetone (14.5–26.1%). PCA analysis showed that (Z)-β-ocimene levels varied significantly across different concentrations of Zn and B. Application of Zn @ 300 mg L−l increased stomatal density and Zn + B @ 200 mg L−l resulted in increased oil gland density.