Seasonal variations influence the phytochemistry and pesticidal potential of Alpinia malaccensis essential oils

Alpinia malaccensis (Burm.f.) Roscoe is an aromatic perennial of the Zingiberaceae family with considerable potential for large-scale cultivation as a sustainable industrial crop due to its essential oil yield and pesticidal bioactivity. The present study examined how seasonal variation affects the phytochemistry and pesticidal properties of A. malaccensis leaf and rhizome essential oils (EOs). Fresh plant material was collected in the last month of each season following IMD classification-September 2021 (monsoon), December 2021 (post-monsoon), early April 2022 (winter), and June 2022 (summer). There was a significant influence of season on the EOs yields. The highest rhizome (0.13%) and leaf (0.15%) EOs yields were recorded in the winter and summer seasons, respectively. Similarly, EO constituents are also significantly influenced by seasons. The main chemical class in leaf EOs was monoterpene hydrocarbons, whereas in rhizome EOs, monoterpene hydrocarbons as well as oxygenated monoterpenes were dominant classes. Further, the EOs were evaluated for their nematicidal (against root knot nematode, Meloidogyne incognita) as well as phytotoxicity against seeds of radish (Raphanus raphanistrum subsp. sativus) and chicory (Cichorium intybus). Leaf and rhizome EOs in the winter season showed the highest nematicidal activity with the lowest LC50 (0.211 μL/mL) and IC50 (0.012 μL/mL) values in nematode mortality bioassay and nematode egg hatchability bioassay, respectively. Similarly, rhizome EOs in summer and leaf EOs in monsoon were found most effective against radish and chicory seeds, with a Seedling Vigor Index of 69.6 and 0.68, respectively. To explore the mechanism underlying nematicidal activity, in-silico molecular docking was conducted using selected ligands and nematode proteins, and overall, the findings highlight the critical role of seasonal variation in modulating the bio-efficacy and chemical profile of A. malaccensis essential oils.