The higher the concentration of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) in a plant, the more it can resist glyphosate. Some plants can duplicate the gene responsible for producing the EPSPS enzyme, meaning they will produce more of the enzyme and better tolerate glyphosate.
Dr Philip Westra of Colorado State University in the US said molecular testing of kochia plants from Colorado, Kansas, South Dakota and North Dakota had confirmed this resistance mechanism is allowing the weed to thrive.
“We get field-level survival of kochia plants at three copies of the EPSPS gene,” he said. “So how many copies do kochia plants need to be resistant?’”
His team is looking at the EPSPS gene itself to try to understand the molecular mechanism that is allowing the gene to create duplicates.
The same gene amplification resistance mechanism has now been identified in three species – Palmer amaranth (Amaranthus palmeri), annual ryegrass (Lolium rigidum) and tall waterhemp (A. tuberculatus).
Going forward, he is keen to investigate if gene amplification will confer resistance to other herbicides and whether the three different plant species use the same mechanism for gene amplification: “The issue we’re interested in is whether the gene amplification will ramp up over time if we continue to use glyphosate and other herbicides,” he said.
Dr Philip Westra,