The pinewood nematode (PWN) Bursaphelenchus xylophilus is a highly pathogenic
plant parasite that greatly affects pine forests. In Portugal, the most affected species is
Pinus pinaster Aiton. Despite great efforts, since its fist detection in 1999, the PWN has
spread through the country, including Madeira Island, having been recently detected in
Spain [1,2]. Containing this pest is of the utmost importance for European pine forest
safeguard.
Since most synthetic chemicals used to control phytoparasites are toxic to humans and
animals, and can accumulate in the soil and in food plants [3], in the present work, the
nematoxic potential of over 80 essential oils (EOs), isolated from the Portuguese flora,
were assessed against the PWN. EOs were isolated by hydrodistillation and analysed by
GC and GC-MS [3]. EOs hydrocarbon and oxygen-containing fractions were obtained as
in [4]. Direct-contact assays, adapted from [3], were performed by adding EOs/methanol
stock-solutions to 50-100 mixed-stage PWN suspensions. After 24h in darkness, dead
and live nematodes were counted under an inverted microscope. Assays were repeated
at least 10 times in two series.
Mortalities ≥96% were obtained with 2μL/mL of the EOs isolated from Cymbopogon
citratus, Eucalyptus citriodora, Mentha arvensis, Origanum virens, Origanum vulgare,
Ruta graveolens, Satureja montana, Syzygium aromaticum, Thymbra capitata, Thymus
caespititius (carvacrol and/or thymol-rich), Thymus vulgaris and Thymus zygis. These
EOs were further tested at 1, 0.5 and 0.25μL/mL. Minimum lethal concentrations (LC100)
<0.4μL/mL, were obtained for the 2-undecanone-rich R. graveolens EO and the carvacrol
and γ-terpinene-rich S. montana and T. capitata EOs. Assays with EO fractions revealed
that the monoterpene-rich nematoxic EOs control PWN through their combined
hydrocarbon and oxygen-containing fractions through additive and/or synergic relations.
As complex mixtures of active components, EOs may prove to be effective nematoxic
age nts
