Palmer amaranth is a high-impact agronomic weed species that has cost the U.S. agriculture industry billions of dollars since its discovery outside of its native range in the southwestern United States and northwestern Mexico. Over the last 20 years, it has moved farther north and now poses a major threat to corn, soybean and cotton growers across the south and Midwest regions.

It is not legal to sell any kind of seed in Minnesota if the seed lot contains Palmer amaranth. The problem is this particular invasive species—which has shown potential to wipe out up to 91% of corn yields, 68% of soybean yields and 54% of cotton yields—is difficult to visibly distinguish from other pigweed species, making identification reliant upon genetic testing.

In a recent study published in Pest Management Science, researchers from the University of Minnesota’s Minnesota Invasive Terrestrial Plants and Pests Center and Colorado State University have developed a new test for identifying Palmer amaranth that is more robust, easier to use and has shown 99.9% accuracy.

Due to rapid spread of herbicide resistance traits in palmer populations, the prevention of Palmer establishment is more important than ever. Researchers hope to make the new test technology commercially available to agronomic professionals across the U.S. by the end of 2021, which can be applied to both individual samples and bulk seed mixes.

To develop the test, researchers collected samples of Palmer amaranth and related species from across the United States, as well as Mexico, South America and Africa. They then performed genomic sequencing on these samples and searched for specific genetic differences between species. The targets identified were then used to design a set of three genetic markers for the identification of Palmer DNA against the DNA of related pigweed species. Finally, those tests were validated for performance against the most robust testing panel assembled to date.

Accuracy for these markers ranged from 99.7% to 99.9%, with only one to three errors against a panel of 1,250 samples. Bulk seed testing showed reliable detection of Palmer at a level of one Palmer seed in a mix of 200 pigweed seeds.

“We believe this has the potential to help prevent palmer seed from being introduced as a contaminant in pollinator seed mixes, bird seed, and other seed lots sold from areas where palmer is currently a problem, into areas like Minnesota,” said co-author Todd Gaines, an associate professor of molecular weed science at Colorado State University. “We also see great potential for this to be used to help protect corn and soybean exports by verifying the absence of Palmer in grain sold to countries that won’t accept Palmer-contaminated products.”

In the immediate future, the research team continues to investigate novel approaches for palmer control, and are currently investigating the potential use of genomic testing to identify palmer presence in soil seed banks.

The research was funded by the Minnesota Invasive Terrestrial Plants & Pests Center through the Minnesota Environment and Natural Resources Trust Fund, and collaborators included University of Minnesota Extension, Colorado State University, Michigan State University and the Minnesota Department of Agriculture.

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