Infection status of sugar beet plants influence infection decisions of root-knot and root lesion nematodes

Abstract

Plant-parasitic nematodes inflict substantial economic losses on a global scale. While there is a substantial body of knowledge concerning plant-nematode interactions, there is a dearth of information regarding plant-pathogen-pathogen interactions when multiple plant-parasitic nematode (PPN) species exist in the vicinity of plants concurrently. In this study, sugar beet plants were employed as a model system to investigate the impact of PPN-exposed and non-exposed plant exudates and volatile organic compounds (VOCs) on the orientation behaviors of two economically significant PPN species, root knot nematode (RKN) Meloidogyne incognita and root lesion nematode (RLN) Pratylenchus neglectus. Additionally, the degree to which the exometabolomes (metabolic footprints) of these PPNs influenced nematode behavior, both conspecifically and heterospecifically was measured. Two-choice Petri dish experiments were conducted using root exudates collected from infected and non-infected plants, and the responses of nematodes to these exudates were measured. Similar experiments were conducted using nematode exometabolomes. To test the impact of plant exudates and VOCs on nematode behavior, olfactometer experiments were conducted by placing plants unexposed to nematodes and nematode-exposed plants at the ends of olfactometer arms and nematode responses were assessed after 18-h for RKN and 48-h for RLN. No significant trend was observed in the choices of RLN in the root exudate experiments. In contrast, RKN responded more strongly to exudates from plants previously unexposed to nematodes compared with plants that were exposed to one day and two days post inoculation. No significant differences were found for either nematode species in the exometabolome experiments. In olfactometer trials, RKNs were attracted to uninfected plants over PPN-infected plants or no plant. In the case of RLN olfactometer trials, significant differences were detected, but no specific trend could be established. This study highlights the conspecific and heterospecific behavioral interactions between nematodes exposed to previously infected plant roots.