Trash-talking weeds stress crops

Crop scientists have long known that plants can communicate with each other about their environment and make decisions about growth based on these conversations. But recent research out of the University of Guelph shows weeds can “talk” a crop plant to death.

corn stalks

(Don Graham,

Plants trade information through chemical signals and changes in sunlight reflected off other plants growing nearby. University of Guelph plant agriculture researcher Clarence Swanton and his team showed for the first time the effect of communication between crop seedlings and nearby weeds.

They discovered corn and soybean seedlings can sense changes in light reflected off the weeds, or as Swanton puts it: “The weeds and the crop seedlings have a chit chat.”

More importantly, Swanton showed that this conversation can stress the crop seedling, and just like humans under stress, the seedlings produce free radicals in response. Free radicals are naturally-occurring molecules that help cells communicate with each other, but when produced in excess damage the cell’s DNA. In this case, the crop seedlings produce too many free radicals.

“The plant must spend energy to repair the damage and this takes energy away from growth,” says Swanton. The subsequent delay in growth can reduce a crop’s yield.

Experimenting with tobacco seedlings and grass-type weeds, Swanton showed that if this conversation goes on too long, a weed can actually talk a tobacco plant to death. The tobacco plant germinates, but dies before reaching maturity. It’s not clear why, but crop seedlings do not have the same reaction to plants of their own species.

Controversial chemical hints at solution

Swanton and his team have also discovered a solution to the damage caused by crop seedlings’ conversation with weeds, albeit a controversial one: a chemical called thiamethoxam. Thiamethoxam is among a class of neonicotinoid pesticides that Ontario started phasing out in 2015 because some studies suggest a link between neonicotoids and the deteriorating health of bees and other important pollinators.

Swanton showed that treating corn seeds with thiamethoxam triggers genes that produce antioxidants, a substance that counteracts free radicals.

While he is not suggesting the wholesale use of thiamethoxam, Swanton says the finding is important because it points to mechanisms for improving a crop’s ability to overcome stress.

This is especially important in an era of climate change. “Improving drought or heat stress tolerance is highly significant in terms of agriculture,” says Swanton. “Perhaps we can create seed treatments that trigger helpful genes in times of stress.”

Swanton and his team are now using what they learned from their research to investigate seed treatments that may one day safely protect crops from trash talking weeds.

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