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Breakthrough

Research team discovers how weeds develop herbicide resistance

research teamGlyphosate-resistant weeds pose a huge problem for Kansas farmers and the state economy. A team of K-State scientists has made a breakthrough in controlling these weeds.    

Researchers have discovered how weeds develop resistance to the popular herbicide glyphosate, the key ingredient in products such as Roundup.

Their work is detailed in the Proceedings of the National Academy of Sciences, known as PNAS and considered to be one of the most-cited journals for scientific research in the world. According to its website, PNAS receives more than 21 million hits per month.

“Herbicide resistance in weeds has been a huge problem, not only in Kansas and the U.S. but many parts of the world,” said Mithila Jugulam, weed scientist in the Department of Agronomy

Jugulam co-authored the PNAS article with plant pathologists Dal-Hoe Koo, Bernd Friebe, and Bikram Gill, university distinguished professor and director of K-State’s Wheat Genetics Resource Center.

The team found the mechanism that makes weeds resistant to glyphosate, the herbicide commonly used in agriculture. 

Palmer amaranth and common waterhemp are troublesome pigweeds in Kansas agricultural fields. The group also published research on common waterhemp in Plant Physiology.

“We found that glyphosate-resistant Palmer amaranth plants carry the glyphosate target gene in hundreds of copies,” Jugulam said. “Therefore, even if you applied an amount much higher than the recommended dose of glyphosate, the plants would not be killed.”

Normally, the genetic material in all organisms — including humans — is found in long, linear DNA molecules, called chromosomes, Gill said.

In glyphosate-resistant weeds, the glyphosate-target gene, along with other genes actually escaped from the chromosomes and formed a separate, self-replicating circular DNA structure. Scientists refer to this structure as extra-chromosomal circular DNA (eccDNA). Each has one copy of the gene that produces an enzyme that is the target for glyphosate.

“Because of the presence of hundreds of eccDNAs in each cell, the amount of the enzyme is also abundant,” Gill said. “Therefore, the plant is not affected by glyphosate application and the weed is resistant to the herbicide.”

“We think that the resistance via eccDNA is transitory: It can be passed to the weed’s offspring and other related weed species,” he said.

Armed with their new knowledge, the researchers can begin work on developing strategies to negate resistance in weeds.

This research was partially funded by grants from the Kansas Wheat Commission; the Kansas Crop Improvement Association; a National Science Foundation grant received through the Wheat Genetics Resource Center; the Department of Agronomy; and USDA’s Agricultural Research Service. K-State worked in collaboration with researchers at Clemson University, the USDA Agricultural Research Service (Mississippi), and Michigan State University.