Chemical characterisation and allelopathic potential of essential oils from leaves and rhizomes of white ginger

Resumo

Essential oils have the potential to be used as bioherbicides, and possess the advantage of their biodegradability, high
structural diversity and reduced natural resistance to weeds. The essential oils of the leaves and rhizomes of Hedychium coronarium,
an exotic invasive plant adapted to different regions of Brazil, were extracted by hydrodistillation and characterised chemically by
Gas-Liquid Chromatography and Gas-Liquid Chromatography/Mass Spectrometry. Allelopathic activity was determined using
methodologies that evaluate the effects of volatility and direct contact on seed germination and seedling vigour in the lettuce. The major
constituents of the essential oil from the leaves were ȕ-pinene (46.9%), Į-pinene (19.2%) and ȕ-caryophyllene (13.2%) and from the
rhizomes, ȕ-pinene (41.5%), 1.8-cineole (23.6%) and Į-pinene (13.1%). When analysing the volatile effects of the essential oils, it was
seen that their concentration did not affect seedling first germination count or total germination. The essential oil from
the rhizomes was more effective than the essential oil from the leaves in reducing seedling response for SGI, dry weight,
and length of the roots and shoots. When evaluating the effect of direct contact with the essential oils, it was seen that
both oils reduced the response of all the variables under evaluation, and that in addition, the oil from the rhizomes
caused greater reductions than that from the leaves, again for all variables. These results can be attributed to the higher
levels of monoterpenes present in the essential oil from the rhizomes, mainly the presence of 1.8-cineole.