Abstract
Plant-parasitic nematodes are detrimental agricultural pests, inflicting 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 concurrently existing around plants. This master's thesis study employed sugar beet plants as a model system to investigate the impact of PPN-exposed and non-exposed plant exudates and volatiles (VOCs) on the orientation behaviors of two significant PPN species, root knot nematode (RKN) Meloidogyne incognita and root lesion nematode (RLN) Pratylenchus neglectus. Additionally, it explored how the exometabolomes of these PPN types influenced each other's behavior, both conspecifically and heterospecifically.For the root exudate testing, hydroponically grown sugar beet plants were inoculated with either 1000 RKN or RLN individuals, with incubation periods of 1-2 and 7 days. Nematode-free plants, incubated for the same duration, served as the control group. Two-choice petri dish experiments were conducted using collected root exudates, and the nematodes' preferences were determined. Similar experiments were established using nematode exometabolomes (metabolic footprints). Olfactometer experiments involved placing 7-day control and nematode-exposed plants at the end of olfactometer arms to assess the nematodes' choices over a 18-hour for RKN and 48-hour for RLN.
Notably, no significant trend was observed in the choices of RLN in the Petri dish experiments. In contrast, RKN exhibited a preference for the clean plant in only one application each in the 1 and 2 DPI experiments. Similarly, no significant differences were found for both nematode species in petri dish experiments involving nematode exometabolomes. However, in olfactometer trials, RKN individuals predominantly selected the non-exposed option over PPN-infected plants. In the case of RLN trials, significant differences were detected, but no specific trend could be established. RLN individuals exhibited a preference for PPN-infected plants in some groups, while choosing the side with empty or clean plants in other groups.
This thesis study highlights the significant impact of root exudates and VOCs on the conspecific and heterospecific behavior of plant-parasitic nematodes. However, the strength of this effect varies depending on the plant and nematode species and days post inoculation. While the results obtained in this thesis study offer insights into the influence of plant root exudates and VOCs on PPNs, further research is essential in the future to gain a deeper understanding of these interaction.