Screening synergistic interactions on essential oils for the improvement of toxicity against the pinewood nematode

Bursaphelenchus xylophilus, commonly known as pinewood nematode (PWN), is considered one of the greatest threats to pine forest ecosystems. The most recent invasion of this phytoparasite occurred in Europe, in Portugal. Pest management strategies based on chemical nematicides are highly effective but can lead to negative ecological impacts and human health concerns. Research on sustainable alternatives is now a priority. The use of essential oils (EOs) as nematicides has gained renewed interest due to the advantages of being easily obtained, biodegradable and showing low toxicity to mammals. The present work aimed at screening the activity of four EOs against the PWN and analyzing possible synergistic interactions, in combinations of two EOs, towards anti-PWN activity. The EOs of Cymbopogon citratus, Eucalyptus globulus, Mentha piperita and Satureja montana were acquired from commercial sources and analyzed with Gas Chromatography coupled to Mass Spectrometry (GC-MS). Anti-PWN activity was screened by determining in vitro nematode mortality at several concentrations of EOs, or EO mixtures, per mL of PWN suspension. The combination of C. citratus and M. piperita EOs resulted in higher activities than those obtained for each one tested solely, suggesting the occurrence of synergistic interactions between the compounds of these EOs. Research on the combination of synergistic EOs may lead the development of plant based biopesticides with optimized activities against the PWN.