In the field, they stand side by side: the robust rye with its tough stems and the humble faba bean with its plump pods. At first glance, it might just look like a mixed crop. But beneath the surface, a chemical drama is unfolding – one that researchers from Aarhus University aim to examine in a new project supported by Independent Research Fund Denmark. Rye excretes defensive compounds — benzoxazinoids — into the soil, and faba beans absorb them like a kind of botanical bodyguard. 

“We’ve discovered that legumes can absorb these compounds from the soil, which makes them more resistant to root-dwelling parasitic nematodes,” explains Professor Mette Vestergård Madsen from the Department of Agroecology at Aarhus University. 

It may sound technical, but the implications could be far-reaching. As we look to reduce meat consumption and increase plant-based protein intake, legumes like faba beans are becoming increasingly important. They’re protein-rich and can be grown locally – but they’re also vulnerable to pests and fungi, which threatens both yield and farmers’ willingness to grow them. 

A helping hand from rye 

Benzoxazinoids – or simply BX, as researchers call them – are naturally occurring chemical compounds that cereals use to defend themselves against pests and diseases. Rye, in particular, is prolific at excreting BX from its roots. And here’s where things get interesting: faba beans can’t produce BX themselves, but they may be able to absorb it from the surrounding soil. 

In earlier studies, researchers showed that other legumes growing near rye absorb BX and transport it from the roots up into the stems and leaves. The hypothesis in this new project is that the benefits may extend beyond underground pests and fungi – potentially protecting the plants from aphids and other aboveground threats as well. 

“It’s like the plant gets an immune booster. We believe BX’s activates the faba bean’s own defence mechanisms, making it more resilient to both pests and diseases,” says Mette Vestergård Madsen. 

A healthy microbiome as a shield 

But the project goes beyond the faba bean’s internal defences. Its roots are part of a whole underground ecosystem – a microbiome of bacteria and fungi – that may also play a crucial role in plant health. Previous research has shown that in maize, BX’s can promote beneficial microbes that help protect against disease. Now researchers want to find out if the same holds true for faba beans. 

“Our hypothesis is that BX’s may also help shape a protective microbiome on the roots of the faba bean,” says Mette Vestergård Madsen. “We’ll be using advanced molecular biology tools to find out how BX’s affects both the plant and its microbial partners.” 

The new project combines plant chemistry, molecular microbiology, and plant physiology with entomology. The goal is to understand precisely how BX’s works — and how it can be used strategically in future farming systems. 

Plant partnerships for the green transition 

For years, faba beans have been something of an underdog in agriculture. They have the potential to replace imported soy, improve soil fertility, and deliver protein for both human and animal consumption. But their vulnerability to pests has been a major barrier. 

This new project could help change that. If the researchers are right, we may soon see more of what they call “functional intercropping” – where plants don’t just share space in a field but actively support each other through natural chemical interactions. 

More Information 

Read more: Learn about the project "Faba bean exploitation of cereal phytochemicals for pest resistance" here 

Professor Mette Vestergård Madsen, Department of Agroecology, Aarhus University , Phone: +45 20 57 94 26 or email: mvestergard@agro.au.dk