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

Abstract

The pinewood nematode (PWN), Bursaphelenchus xylophilus, induces shoot yellowing and wilting by injuring pine vascular tissues and resin canals. In Asia, it devastated wide forests of susceptible pine, causing drastic ecological, economic and cultural repercussions. In 1999, it reached Europe (Portugal) and despite the actions of the authorities, it rapidly advanced to the border areas of Spain, threatening the European pine forests. Chemical control is used in Asia with remarkable success, yet most nematicides are dangerous to human health and the environment. Natural volatile allelochemicals (VA) and derivatives are sustainable alternatives, providing many advantages to commercial nematicides. The present work summarizes available bibliographic information on VAs with activity against the PWN and reviews the chemical properties leading to nematoxicity. Published works reported over 250 VAs in direct contact assays. Compounds highly active against the PWN belong to monoterpenoid, phenylpropanoid and aliphatic alcohols, aldehydes, ketones, carboxylic acids, esters and sulphide groups. The presence of highly electronegative elements in these structures appears to increase activity. Trisulphides, coumarins, medium carbon chain length aliphatic alcohols and derivatives composed the top 5 most active allelochemicals. An indication of their mechanisms of action can be obtained from studying the reported structure-activity relationships. Keywords: Bursaphelenchus xylophilus; monoterpenoids; nematicide; oxygenated aliphatic compounds; phenylpropanoids; pinewood nematode; sulphides; toxicity