North American Waterhemp Now a Pesky Weed that Reduces Crop Yields, Research Reveals Modern Agriculture to Blame

According to research, modern agriculture is to blame for the North American waterhemp becoming a pesky weed that lowers crop yields.

At the University of British Columbia, a multidisciplinary team of researchers has discovered how the spread of modern agriculture has turned the common waterhemp, a native plant of North America, into a destructive agricultural weed.

187 Samples of Waterhemp

In the study, 187 samples of waterhemp from present-day farms and nearby wetlands were compared to more than 100 historical samples from museums in North America that date back to 1820.

The researchers were able to see evolution in action in various environments by examining the genetic makeup of the plant over the past two centuries.

Dr. Julia Kreiner, a Department of Botany postdoctoral researcher from UBC, said that as agricultural intensification increased in the 1960s, the genetic variations that help the plant thrive in contemporary agricultural environments have remarkably quickly risen to high frequencies.

Kreiner is the first author of the study published recently in the journal Science.

Imposed Changes and Genetic Adaptations

The weed's genome contains hundreds of genes that help it thrive on farms, and the researchers found that mutations in genes involved in rapid growth, drought tolerance, and herbicide resistance frequently occur.

Kreiner said that humanity is imposing changes on agricultural landscapes that are so significant that they have an impact on nearby habitats that most people would consider to be natural.

The research could help in conservation efforts to protect natural areas in agriculturally-dominated landscapes.

To lessen the evolutionary impact of farms, reduce gene flow from agricultural areas, and protect more secluded natural populations.

Native to North America, common waterhemp wasn't always a bad plant. Yet due to genetic modifications, such as herbicide resistance, the weed has recently grown to the point where it is almost impossible to remove from farms.

Dr. Sarah Otto, Killam University Professor at the University of British Columbia, said that While it usually grows near streams and lakes waterhemp has undergone genetic changes that enable it to thrive in drier areas and grow quickly enough to outcompete crops.

Otto, a co-author of the study, added that Given how strongly it has been selected to flourish alongside human agricultural activities, waterhemp has essentially evolved to become more of a weed.

According to Montana State University, herbicides have largely failed to control waterhemp, which lowers crop yields particularly when infestations are dense.

Herbicides for corn and soybeans are efficient, but the few post-emergent possibilities for pulse crops, canola, flax, sunflower, and other small-scale crops make control very challenging.

Herbicide-Resistant Mutations

Notably, the historical samples lacked five of the seven herbicide-resistant mutations discovered in the current samples.

According to Kreiner, modern farms place a strict filter on the different species of plants and mutations that can endure over time.

Herbicides served as one of the most effective agricultural filters, determining which plants persisted and which died when the genes of the plant were sequenced.

Since 1960, waterhemp with one of the seven herbicide-resistant mutations has produced 1.2 times as many surviving offspring annually as plants without the mutations.

Although less frequently, herbicide-resistant mutations have also been found in natural habitats, which raises concerns about the costs associated with these adaptations for plant life that are in non-agricultural settings.

According to Kreiner, the changes taking place on farms are affecting how fit the plant is in the wild because being resistant to herbicides can cost a plant money.

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Farming, Climate Change, Rapid Plant Evolution

Agricultural methods have also altered the geographic distribution of specific genetic variants.

A weedy southwestern variety has moved steadily eastward across North America over the past 60 years, introducing its genes into native populations as a result of its competitive advantage in agricultural settings.

Dr. Stephen Wright, a University of Toronto professor, said that These findings demonstrate the enormous potential of historical genome research for understanding short-term plant adaptation.

Wright said that The current understanding of how agriculture and climate change are accelerating plant evolution will be expanded by extending this research across scales and species.

According to John Stinchcombe, a professor from the University of Toronto and co-author of the study, "An essential next step in their work is to comprehend what happens to these variants and how they impact populations of plants that do not come from farms," SciTech Daily reported.