MINNEAPOLIS — Palmer amaranth is a weed species that has cost the United States agriculture industry billions of dollars since its discovery outside of its native range in the southwestern U.S. and northwestern Mexico. Over the last 20 years, it has moved further north, and now poses a major threat to corn, soybean and cotton growers across the south and Midwest.
It is not legal to sell any kind of seed in Minnesota if the seed lot contains Palmer amaranth, according to a University of Minnesota news release. The problem is this particular invasive species — which has shown potential to wipe out up to 91% of corn yields and 68% of soybean 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 (MITPPC) and Colorado State University have developed a new test for identifying Palmer amaranth that is easier to use and — most importantly — 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 United States by the end of 2021.
“Development of tools and weed seed regulations play important roles, but ultimately it all comes back to the growers,” said lead author Anthony Brusa, a postdoctoral associate in the College of Food, Agricultural and Natural Resource Sciences. “Prevention of Palmer is a team effort. So far, every initial sighting of Palmer in Minnesota was from a grower, and control efforts wouldn’t be possible without their help.”
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 related pigweed species.
“The gates are open for developing tests for herbicide resistance, seed contamination and seed bank diversity,” said co-author Eric Patterson, an assistant professor and weed geneticist at Michigan State University.
Accuracy for these markers ranged from 99.7-99.9%, 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 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,” said co-author Todd Gaines, an associate professor of molecular weed science at Colorado State University.
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.