Identification of Repellents from Four Non-Host Asteraceae Plants for the Root Knot Nematode, <i>Meloidogyne incognita</i>

Abstract

Olfactory cues guide plant parasitic nematodes (PPNs) to their host plants. We tested the hypothesis that non-host plant root volatiles repel PPNs. To achieve this, we compared the olfactory responses of infective juveniles (J2s) of the PPN <i>Meloidogyne incognita</i> to four non-host Asteraceae plants, namely, black-jack (<i>Bidens pilosa</i>), pyrethrum (<i>Chrysanthemum cinerariifolium</i>), marigold (<i>Tagetes minuta</i>), and sweet wormwood (<i>Artemisia annua</i>), traditionally used in sub-Saharan Africa for the management of PPNs. Chemical analysis by coupled gas chromatography-mass spectrometry (GC/MS) combined with random forest analysis, followed by behavioral assays, identified the repellents in the root volatiles of <i>B. pilosa</i>, <i>T. minuta</i>, and <i>A. annua</i> as (<i>E</i>)-β-farnesene and 1,8-cineole, whereas camphor was attractive. In contrast, random forest analysis predicted repellents for <i>C. cinerariifolium</i> and <i>A. annua</i> as β-patchoulene and isopropyl hexadecanoate. Our results suggested that terpenoids generally account for the repellency of non-host Asteraceae plants used in PPN management.