Phenological Stage Specific Variations in Chemical Compo-sition, Antioxidant and Antimicrobial Properties of the Essential Oils of Aerial Parts of Monarda didyma L. Cultivated Under Doon Valley Climatic Conditions of Uttarakhand, India

This study aims to evaluate the variations in yield of essential oil, chemical constituents, antimicrobial and antioxidant potential of Monarda didyma L. (aerial parts) at three different phenophases, namely vegetative stage, full blooming and maturity (seed setting) stages. The essential oil content ranged from 0.62-0.75% in whole aerial parts, with the highest yield in the full flowering (0.75 +/- 0.042%), followed by pre flowering (0.70 +/- 0.033%) and seed setting (0.62 +/- 0.052%) stages. Linalool was found as the major compound followed by gamma-terpinene, thymol methyl ether, p-cymene and thymol in the oils during different phenophases of plant. Linalool was maximum in vegetative (pre flowering) stage (60.15 +/- 1.56%) as compared to full blooming (44.32 +/- 2.55%) and seed setting (46.49 +/- 1.63%) stages respectively. gamma-Terpinene, the second major constituent was found to be maximum in full blooming stage (21.06 +/- 3.06%) as compared to the other stages, and showed cogent variations in percent composition of gamma-terpinene during different phenological stages. In thymol methyl ether content, significant variation was observed during all three phenophases of plant. The antioxidant (DPPH assay) activity showed that M. didyma oil has maximum activity at seed setting stage. The maximum antimicrobial activities in oil was active at vegetative phase of plant against bacteria and yeast i.e., Bacillus sp., E. coli, L. monocytogens, P. aeruginosa, S. aureus, C. albicans and revealed favourable values of MIC (0.5% to1% v/v) and MBC/MFC (0.5 to 2% v/v) against bacterial and yeast cultures.