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Several plant species are known to control plant-parasitic nematodes in soil by producing nematicidal volatile organic compounds (VOCs). However, the VOCs activity of many plant species against root-knot nematodes is still unknown. Here, we investigated VOCs emitted from leaves of citronella (Cymbopogon nardus L.) or black pepper (Piper nigrum L.), broccoli shoots (Brassica oleracea L.) and Brazil nuts (Bertholletia excelsa Bonpl.) against second-stage juveniles (J2) and eggs of Meloidogyne incognita. In vitro assays revealed that VOCs emitted from dry plant macerates decreased J2 motility to almost 0% and reduced egg hatching by 47% in comparison with the control. The water exposed to VOCs from citronella, black paper and Brazil nuts decreased the motility of the J2 by 42%, whereas broccoli reduced it to almost 0%. Furthermore, VOCs from Brazil nuts and broccoli shoots killed J2 and reduced the number of galls and eggs in tomato roots under greenhouse conditions. Purified dimethyl sulfate (DMS), dimethyl disulfide (DMDS) and 3-pentanol, previously identified in the broccoli volatilome, were tested on eggs of M. incognita. DMDS and 3-pentanol were shown to reduce egg hatching by 96.8% at 176 mg/L and by 88.4% at 918 mg/L, respectively, whereas DMS increased egg hatching by 13% at 500 and 1000 mg/L. All plant species produced VOCs toxic to eggs and J2, which are the most important developmental stages in terms of nematode management and should be more exploited to reduce root-knot nematode populations in soils prior to host infection or used for prospection of novel nematicidal products. |
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