Maize defence compound helps parasitic nematodes find their host

Root-knot nematodes (Meloidogyne incognita) are among the most damaging plant parasites worldwide. They invade roots, form galls, and disrupt the uptake of water and nutrients, resulting in significant yield losses in many crops. Yet how these microscopic animals manage to locate their host plants in the complex soil environment has long remained unclear.

An international research team, led by Zhejiang University in China and with an important contribution from Wageningen University & Research, now shows that maize plants themselves inadvertently play a role. Maize roots release benzoxazinoids (BXs), chemical compounds known for their defensive effects against insects. In this study, the researchers focused on one specific compound: MBOA, a breakdown product of benzoxazinoids that enters the soil via the roots.

“These compounds are usually viewed as direct defence chemicals,” says WUR researcher Jose Lozano Torres, who was involved in the study. “What we show is that, in this case, they have an indirect effect that actually helps parasitic nematodes.”

That help does not occur directly. In sterile soil, without micro-organisms, the nematodes showed little response to MBOA. Only in living soils were they strongly attracted to the roots. This pointed the researchers towards a crucial role for the soil microbiome.

“MBOA changes the composition of the microbiome around the roots,” Lozano Torres explains. “It promotes specific bacteria, while others decline. That shift turns out to be essential for what happens next.”

The bacteria enriched by MBOA, including species from the genera Pseudomonas and Citrobacter, produce volatile organic compounds. Two compounds in particular, 1-undecanol and 2-phenylethanol, proved to be key. These volatiles spread through the soil and act as signals for the nematodes.

“The nematodes detect these bacterial compounds and use them as a kind of scent trail to find the roots,” says Lozano Torres. “They do not need to sense the plant itself directly.”

That this is no coincidence is shown by experiments focusing on the nematodes themselves. The researchers identified three chemosensory genes required for detecting the bacterial volatiles. When these genes were silenced, the nematodes effectively lost their ability to ‘smell’. They no longer responded to the volatile compounds and were largely unable to locate the roots.

“By blocking those genes, we effectively blinded the nematodes to the signals coming from the microbiome,” Lozano Torres says. “Without that bacterial intermediary, the whole mechanism breaks down.”

According to the researchers, this provides a clear example of what they describe as ‘ecological hijacking’. A parasite exploits communication between a plant and its microbiome for its own benefit, offering a fundamentally different perspective on the role of plant defence compounds.

“It shifts the focus from a direct interaction between plant and parasite to a system with three players,” says Lozano Torres. “The plant, the microbiome, and the nematode are all tightly connected.”

The findings are directly relevant for agriculture and plant breeding. Many breeding programmes select for higher levels of benzoxazinoids to reduce insect damage. This study shows that such strategies can have unintended side effects.

“Varieties that are well protected against insects may at the same time become more attractive to nematodes,” Lozano Torres says. “That means breeders may need to reassess the balance between different defence traits.”

Soil management also emerges as a potential lever. Because the attraction depends on specific bacteria, it may be possible to steer the microbiome deliberately. This could involve promoting bacteria that do not produce attractive volatiles, or that outcompete the species involved.

Finally, the researchers point to new avenues for nematode control. The identified olfactory receptors could serve as targets for compounds that disrupt the nematodes’ ability to orient themselves, without relying on broad-spectrum and often harmful nematicides.

Read the scientific paper in Nature Plants.