A review on the nematicidal activity of volatile allelochemicals against the pinewood nematode

Pine wilt disease (PWD) is caused by the pinewood nematode (PWN), Bursaphelenchus xylophilus. This invasive microscopic phytoparasitic nematode induces pine yellowing and wilting by feeding on pine vascular tissues and resin canals and multiplying rapidly. In Asia, PWD has devastated wide areas of susceptible pine forests, with drastic ecological, economic and cultural repercussions. In 19991, Portugal became its entry point into Europe, most likely through imported goods from Asian countries, and, despite the actions of the authorities, has advanced rapidly into the border areas of Spain, threatening European pine forests. Chemical control has been used in Asia with remarkable success, yet most nematicides are dangerous to human health and the environment. Natural volatile allelochemicals and derivatives are sustainable and ecological alternatives, providing many advantages to commercial nematicides2,3. The present work summarizes available bibliographic information on the most successful volatile allelochemicals showing activity against the PWN and reviews the chemical properties leading to anti-PWN nematicidal characteristics. Published work reports over 110 allelochemical volatiles, mainly secondary metabolites, with considerable activity against the PWN. These belong to highly active classes of chemical compounds, namely monoterpenoids, phenylpropanoids and aliphatic alcohols, aldehydes, ketones, carboxylic acids, esters and sulphides. Volatiles with highly electronegative elements appear to show increased activity. The top 10 most active allelochemicals (lowest half maximum effective concentration, EC50) were trisulphides, stilbenoids and medium carbon chain length aliphatic alcohols and derivatives. Future research must deepen the study of the strong structure-activity relationships reported to understand the mechanism of action of these highly nematicidal anti-PWN volatiles. This knowledge is paramount in the establishment of an integrated and sustainable approach to manage PWD in its new forest environment. 1. Mota, M. et al. First report of Bursaphelenchus xylophilus in Portugal and in Europe. Nematology 1, 727–734 (1999). 2. Faria, J. M. S., Barbosa, P., Bennett, R. N., Mota, M. & Figueiredo, A. C. Bioactivity against Bursaphelenchus xylophilus: Nematotoxics from essential oils, essential oils fractions and decoction waters. Phytochemistry 94, 220–228 (2013). 3. Barbosa, P. et al. Bioassays against pinewood nematode: Assessment of a suitable dilution agent and screening for bioactive essential oils. Molecules 17, (2012).