Medicinal plant volatiles applied against the root-knot nematode Meloidogyne incognita

Despite several works revealing different plant species producing volatile organic compounds (VOCs) toxic to plant-parasitic nematodes, nematicidal activities of VOCs are poorly investigated in medicinal species. Therefore, this work focused on exploring the activities of VOC emitted from medicinal plant leaves against the root-knot nematode (RKN) Meloidogyne incognita. By in vitro assays, leaves of thirteen medicinal species emitted VOCs that significantly immobilize the second-stage juveniles (J2) of M. incognita, although only VOCs from Cymbopogon nardus and Dysphania ambrosioides killed more than 40% of J2. Thereafter, water exposed to VOCs from C. nardus or D. ambrosioides immobilized 46% and 79% of the J2, respectively. The galls and eggs of RKN were significantly reduced in tomato plants when the J2 were previously exposed to VOCs from C. nardus and D. ambrosioide at a concentration of 1.5% (w/w). Soil biofumigation using C. nardus and D. ambrosioides reduced the number of galls by 19% and 37%, respectively, by applying 2.4 g (2%) of macerates and reduced 80% the number of eggs by applying 9.6 (8.0%). The GC-MS identified compounds previously described as nematicidal compounds from both C. nardus and D. ambrosioides. The compounds ascaridole and citronellal, intensely emitted from D. ambrosioides and C. nardus, respectively, have already been described as toxic to RKN. However, isopulegol, dodecane and α-ionone from their volatilomes did not exhibit nematicidal effects. Nonetheless, D. ambrosioides and C. nardus produce VOCs toxic to RKN and should be exploited as biofumigant plants. Furthermore, nematicidal VOCs may represent new options for commercial products.