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Weedy Rice Keeps On Evolving Roots That 'Cheat'

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Scientists have decoded how weedy rice, an aggressive variant of rice, out-compete other crops and take over an entire field.

A team from Washington University in St. Louis and the Donald Danforth Plant Science Center revealed that weedy rice has evolved "cheater" roots that minimize below-the-ground contact with other plants and exploit the nutrient-sharing quality of the soil in fields. The "cheater" roots give weedy rice an unfair advantage over competing crops.

"We tend to think of competition occurring above ground because that's the part of the plant we see," said Kenneth M. Olsen," professor of biology at Washington University and senior author of the study. "But that's only half the plant."

Weedy Rice's Cheater Roots

In the study published in the journal New Phytologist, the researchers demonstrated how the weedy rice take root in a field and take over. The team focused on two evolved types of weedy rice often found in the same fields in the southern United States.

They used new imaging techniques, including a semi-automated optical tomography approach, the team took photographs of the root system of 671 weedy rice plants, modeled the photos in 3-D, and created 360-degree models of weedy rice roots.

They also used an algorithm to record 98 physical traits of the root system, including depth and width, and genetic analysis to track the history of the weeds.

They found that both types of weedy rice evolved similar traits, but through different genetic mechanisms. The study proves that there is more than one way to evolve a weed, both above the ground and below.

"In other words, it's disconcertingly easy to evolve a weed from a domesticated crop," added Olsen. "This can occur multiple times independently from different crop varieties."

Below The Ground Competition

The study is one of the first to study a plant's root system, including growth and interaction that affect how it competes for nutrients found in the soil. Olsen explained that the "hidden half" of the plants is sometimes more important for survival than the above-ground part. The root system is responsible for essentials such as water and nutrients.

Especially for weedy rice, root growth is more important for competition than above-ground growth.

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