Direct antagonistic effect of entomopathogenic nematodes and their symbiotic bacteria on root-knot nematodes migration toward tomato roots

Aims Negative interactions in the rhizosphere between entomopathogenic nematodes (EPNs) and plant-parasitic nematodes, such as root-knot nematodes (RKNs), have been documented over the past two decades but the mechanisms and dynamics of such interactions remain largely elusive. Methods Here, we evaluated the effect of the inoculation position of two EPN species, Steinernema feltiae and Heterorhabditis bacteriophora , as well as different facets of the EPN-bacterial symbiont complex on the migration of RKNs toward tomato roots, both in sand and in Pluronic gel conditions. Results When EPNs were placed between the position of the RKNs and the roots, the movement of RKNs toward the roots was inhibited. We observed this same pattern both in sand and in Pluronic F-127 (PF-127) gel for two species of EPNs. We also observed that different components of the EPNs/bacterial symbiont complex (bacteria separate from the nematodes vs. the nematode-bacterium complex), and particularly the cell-free supernatant produced by the bacterial culture, displayed inhibitory effects on RKNs. Conclusion Therefore, the EPNs/bacterial complex, by slowing down the movement of RKNs toward the host plant roots, could partially contribute to RKN control. By screening for the most repulsive strains of EPNs that are also effective against insect pests, the combined target approach should alleviate EPNs application costs in integrated pest management practices.