Waterhemp, a common weed has become increasingly resistant to atrazine and other herbicides in recent years. Every time farmers attack the weed with a new herbicide, waterhemp becomes resistant to it, reducing or eliminating the efficacy of the chemical.

University of Illinois weed scientists Dean Riechers, Rong Ma, and Josh Skelton focused on metabolic resistance to atrazine, a chemical that has been used for decades and is still sprayed on approximately 80 percent of the corn acreage in the United States. The team knew from previous research that resistant waterhemp metabolizes atrazine with a class of enzymes known as GSTs. Plants have around 50-120 GST genes, Riechers says.

Candidate GST proteins from waterhemp were isolated and observed for their expression in resistant and sensitive plants. One of the GST proteins was extremely abundant in resistant plants, but almost nonexistent in sensitive plants. The team looked more closely at the gene encoding that GST protein, and its variants or alleles. They noticed that when two dominant alleles for this gene were present, it took more than 14 times the recommended atrazine rate to damage the plants. Plants with just one copy of the dominant allele had a much higher injury, compared to the resistant plants with two copies of the dominant allele, which did not show any damage at all.

For more details about this research, read the article in the ACES College News.