In a quiet Danish greenhouse, white clover roots reach into the soil, unaware they are about to borrow a secret weapon from their neighbour. Just centimetres away, rye plants are quietly secreting benzoxazinoids, potent chemical compounds that plants use to fight pests.

“We wanted to see if plants could actually share their defences,” says Jawameer Hama from the Department of Agroecology at Aarhus University, lead author of the study. “It’s a fascinating idea, almost like borrowing armour from your neighbour.” 

The problem

Root-knot nematodes are tiny but devastating pests. They invade plant roots, stunt growth, and cost farmers millions in lost yields. Pesticides targeting nematodes (nematicides) are banned, because they are harmful to both humans and the environment, leaving farmers with no efficient pesticides for nematode control. 

“Due to their biology root-knot nematodes are extremely difficult to manage,” professor Mette Vestergård explains. “Nematicides are not an option. So, we wanted to explore a natural alternative.” 

The discovery

The team found that clover can absorb rye’s natural defence chemicals through its roots. These compounds, benzoxazinoids (BXs), are well-known for protecting cereals like rye against pests.

“When we analysed the clover roots, we detected eight different BX compounds,” Jawameer Hama explains. “Three of them even moved up into the shoots. That was a clear sign that the transfer was real.” 

And the effect was striking: clover plants that absorbed BXs were significantly more resistant to nematode invasion and reproduction. “In some cases, nematode numbers dropped by more than 60%,” Jawameer Hama notes. “That’s a huge reduction without a single drop of pesticide.” 

Why it matters

This discovery opens the door to a new kind of pest management, one that relies on plant partnerships.

“Imagine reducing pest attacks simply by choosing the right plant combinations,” Jawameer Hama says. “That’s a win for farmers and for the environment.” 

The catch

There’s a trade-off. Clover grown with rye had lower biomass: up to 78% less in some cases. It is likely due to competition and chemical interactions. Meanwhile, this growth penalty was only seen for clover plants that were grown with rye for extended time.

“We saw that clover paid a price for this protection,” Jawameer Hama explains. “The plants were smaller, probably because rye was competing for resources and releasing compounds that affect growth.” 

The bigger picture

This research taps into the concept of “associational resistance,” where plants in diverse communities help each other fight pests. It suggests that future farming could be designed like ecosystems; complex, cooperative, and resilient.

“Plants are not passive,” Mette Vestergård says. “They communicate, they share, and sometimes, they lend each other their weapons. That’s something we can learn from in agriculture.”

More information

Collaborators: Department of Agroecology at Aarhus University       

Funding: Funding from Independent Research Fund Denmark (grant no. 1032-00188B). Acknowledging Eugene JGG Driessen for soil collection, and Danish Agro for rye seed donations.

Conflict of interest: None declared

Read more: The publication “Transfer of chemical defence from rye to clover is associated with enhanced clover resistance against root-knot nematodes” is published in New Phytologist. It is written by Jawameer Hama, Bente Laursen, Inge Fomsgaard, and Mette Vestergård. 

Contact: Tenure Track Assistant Professor Jawameer Hama, Department of Agroecology, Aarhus University. Mail: jawameer@agro.au.dk

Communications Advisor Camilla Brodam Galacho, Department of Agroecology, Aarhus University. Tel.: +45 9352 2136 or mail: brodam@agro.au.dk