Corn plants communicate with each other to defend themselves when they are close together.

Corn plants whisper messages to each other to defend themselves against their enemies. When they are close together, a volatile substance they release induces their neighbors to produce compounds that stunt their growth, but activates their defenses against pests. Not only that, they modify the soil microbiome with which they interact, leaving a defensive legacy in the soil that prepares the immune system of the next generation. The discovery, published in Science , opens the door to the use of the plant's own substances as pesticides.

With an impeccable experimental design, a group of Chinese, Swiss, and Dutch researchers sought to investigate the optimal conditions and consequences of high-density corn cultivation. For several decades, planting corn and other grasses, such as wheat and rice, in close proximity has allowed for increased production of these staples for the world's population. But all overcrowding has its risks: if a pest enters, it will have an easier time spreading, as human viruses clearly demonstrate.

What they did was plant fields at a low density of 60,000 plants per hectare, and others at double that, 120,000/ha. They found that, while there were no major differences at the edges of both, the plants inside the overcrowded fields modified their root systems and reduced the height at which the ears grew, the chlorophyll concentration, and the number of kernels per ear. They thus confirmed that density affects growth. But they also observed significantly less pest damage where the ears grew closer together.

“Our initial hypothesis was that at high plant densities, neighboring plants are closer together, which intensifies chemical signals, while at low densities these signals may be too weak to trigger significant responses,” Lingfei Hu, a researcher at Zhejiang University in China and co-author of the experiments, said in an email.

To try to discern what chemical signals corn uses, they planted hundreds of seedlings at different densities of 50, 100, 150, and even 200 fingerlings per square meter. When they had grown to their fourth leaf, they removed the plants but kept the soil, planting new ones in it. They then saw that the higher the density, the better the corn resisted four of its worst enemies: the fall armyworm, which devours its leaves; the nematode Meloidogyne incognita , a parasite that preys on the roots; northern corn leaf blight, a fungus that reduces yield; and black-stripe dwarf virus, which originated in rice and has jumped to this grass. There was something in the air, the soil, or both, protecting them.

After ruling out genetics, they tested different varieties and analyzed the presence of volatile organic compounds (VOCs) emitted by corn leaves into the environment. They found that in densely cultivated fields, the most abundant VOC was linalool. This is an alcohol present in many plants, especially aromatic or citrus fruits, whose scent is reminiscent of lavender. “It's a constitutively released volatile, emitted under normal conditions. Isolated plants also release it,” Hu recalls. By constitutive, he means that it's standard in the leaves, unlike other compounds that the plant only produces when it's attacked or stressed.

Linalool shows its full power when corn is in close proximity. “We still don't know the exact concentration needed to trigger a response in neighboring plants,” Hu acknowledges. But when it reaches a critical threshold, the corn prepares for war. In less than three days, the surrounding plants have changed their metabolism, producing increased amounts of hormones like jasmonic acid that reactivate their immune systems. And the roots exude compounds called benzoxazinoids, which have pesticidal properties. One of the first things they do is affect the rhizosphere, the symbiosis between beneficial fungi and roots, and the entire soil microbiota. This causes the immune system to go on alert. The release of linalool, the biosynthesis of hormones, and the exudation of benzoxazinoids are all connected.

“A plant releases linalool, which causes changes in the metabolism of others, changes that have an effect on soil bacteria, an effect that remains long after the plant is gone,” summarizes Sergio Ramos, an evolutionary ecologist at the University of Zurich and researcher in the field of corn volatiles. As Ramos, who was not involved in this work, points out, “corn is among the world's top crops by area, and has been so studied that its chemical communication is known in detail.” But the wonder of how this happened was unknown. “Corn is able to identify the insect that is eating it by the proteins in its saliva.” This activates the production of induced volatiles, which only appear after the attack. But linalool is not induced; it is always present. However, as this researcher points out, it only generates a response over short distances: “all volatiles tend to increase.”

For Lucía Martín, a researcher at the Biological Mission of Galicia (MBG-CSIC), the most relevant aspect of this work, although she has been amazed by everything about it, is the legacy effect on the soil. "It works like a vaccine, preparing the immune system of the next generation," she says. Martín wrote her thesis investigating volatiles in potatoes; she is now studying them in other plants such as cotton, and in a few weeks she will travel to Sweden to investigate this legacy effect. She discovered how the attack of moth larvae on potato plants induced the release of volatiles that, in turn, activated the defenses of other plants, making them more resistant.

One of the few weaknesses the researcher sees in the investigation with corn plants, also highlighted by Ramos, is that although they demonstrate the triggering role of linalool, they don't explain how neighboring plants hear , smell , or perceive its aroma. "Several possible receptors have been identified in other plants, but research is still ongoing," she acknowledges. In 2024, the journal Science also published a study that had identified a receptor in the pistil of petunias for a specific volatile, germacrene. But nothing more is known.

Although this wasn't the study's objective, it points to the possible use of certain volatiles in agriculture. For example, where there is a greater risk of pests, the release of linalool could be induced or even dispersed in its synthetic version, which is available. Claude Becker, a biologist at the University of Munich (Germany), wrote a commentary on the research by Hu and his colleagues, also in Science . In an email, he recalls that "they grew barley and ryegrass [a type of grass] on soils that previously had high-density corn; it turned out that they showed stronger defenses against herbivores." So, for him, "in a way: yes, linalool seems to have a general (indirect) effect on the anti-herbivore defense of plants that perceive it." But Becker also notes that they didn't compare the magnitude of the effect with that of an actual herbicide.

There's one last problem for Becker, also highlighted by Ramos, Martín, and even the authors: "There's the disadvantage that the effects of linalool also lead to smaller plants," says the German researcher. It's almost mechanical; resources are limited, and they either dedicate them to growth or defense. But this points to another possibility: where there's no danger, cutting off communication—that is, inhibiting linalool production—could accelerate plant development.