Effect of small lipophilic molecules in tomato and rice root exudates on the behaviour of Meloidogyne incognita and M. graminicola
Plant chemicals in the rhizosphere originating from root exudates or sites of previous nematode penetration can influence nematode behaviour, and a number of plant compounds, some present in root exudates, have been shown either to attract nematodes to the roots, or to result in repellence, motility inhibition, or even death. The present work was conducted to isolate small lipophilic molecules (SLMs) emitted by root exudates of Solanum lycopersicum and Oryza sativa to investigate their effect on root-knot nematodes. SLMs extracted, through solid phase extraction, from hydroponically collected root exudates of 40 tomato and rice plants had an inhibitory impact on the motility of second-stage juveniles of Meloidogyne incognita and M. graminicola and showed a nematotoxic or nematostatic (upon dilution) effect on both species. The semiochemicals present in the SLMs induced a very small, albeit statistically significant, effect on stylet thrusting. A small quantity of salivary secretion around the stylet tip and a significant decrease in nematode head movement were observed. The semiochemicals negatively influenced behaviour of M. incognita and M. graminicola by strongly affecting their mobility. Therefore, it is proposed that SLMs present in both tomato and rice root exudates play important roles during the interaction of Meloidogyne spp. with their host plant, and that they might exert a repellent, or allellopathic, effect on these nematodes.