Weeds typically develop resistance one of two ways: target-site resistance or metabolic resistance. Researchers at the University of Illinois found a way to identify the specific enzyme responsible for metabolic resistance in atrazine-resistant waterhemp.

When weeds display metabolic resistance they use one of hundreds of enzymes to render the herbicide ineffective. Researchers combed through the hundreds of enzymes that could be responsible for resistance to find the one responsible.

Researchers knew from previous research waterhemp’s resistance is found in GST enzymes, but plants have 50 to 120 GST genes. They eventually found the specific responsible gene by narrowing it down to the exact gene pool and isolating specific GST proteins. After isolation, they analyzed their populations in resistant and sensitive plants. One GST protein was scarce in sensitive plants but plentiful in resistant plants.

Plants with the abundant resistant genes took 14 times the recommended rate of atrazine to show damage, while sensitive plants with fewer of those genes showed significant damage. More testing and detailed molecular data gives Illinois researchers confidence they’ve truly found the gene responsible for metabolic resistance to atrazine in waterhemp.

“We think we found the needle in the haystack,” says Dean Riechers, University of Illinois weed scientist in a recent news release. “As long as we know the gene, you could potentially knock it out and make it sensitive again.”

This test can be applied in other broadleaf weeds to find enzymes responsible for resistance. In addition, this information can help chemical manufacturers develop new chemicals to control broadleaf plant pests.

“You could design a GST-inhibiting chemical that’s specific to this one GST [to create new, effective chemistry for waterhemp,” Riechers says.