Glyphosate Resistance

Glyphosate Resistance



Glyphosate is best known as the active ingredient in Roundup-branded herbicides, and the herbicide used with “Roundup Ready” genetically modified organisms (GMOs) (2020). Due to overuse of the herbicide, glyphosate resistance has evolved in many weeds including several Amaranth species. Glyphosate resistance had been linked to an increase in the amount of target-site protein, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). EPSPS’s protein levels and activity both increased as the number of EPSPS genomic copies increased. The effect of the additional copies becomes additive and additional copies confer higher levels of resistance (Gaines et al., 2010).

NAGC validated a DNA-based test for determining EPSPS gene copy numbers using assays published by others (Gaines et al., 2010; Ma et al., 2013; Giacomini et al., 2017). The test and estimated number of EPSPS gene copies for leaf samples is normalized to that of a single copy genetic marker (acetolactate synthase; ALS) within the genome. This test provides faster preliminary results to growers on the glyphosate resistance potential of pigweeds in their fields. Additionally, this test will provide weed scientists a rapid method to screen for herbicide resistance during their experiments in the greenhouse and field.

This project was funded in part by the North Dakota Department of Agriculture Bioscience Innovation Grant, the North Dakota Soybean Council, and the North Harvest Bean Growers Association


  1. Glyphosate Fact Sheet [Online]. United States Environmental Protection Agency,. Available:

Gaines, T. A., Zhang, W., Wang, D., Bukun, B., Chisholm, S. T., Shaner, D. L., Nissen, S. J., Patzoldt, W. L., Tranel, P. J., Culpepper, A. S., Grey, T. L., Webster, T. M., Vencill, W. K., Sammons, R. D., Jiang, J., Preston, C., Leach, J. E. & Westra, P. 2010. Gene amplification confers glyphosate resistance in Amaranthus palmeri. Proceedings of the National Academy of Sciences, 107, 1029-1034.

Giacomini, D., Westra, P. & Ward, S. M. 2017. Impact of Genetic Background in Fitness Cost Studies: An Example from Glyphosate-Resistant Palmer Amaranth. Weed Science, 62, 29-37.

Ma, R., Kaundun, S. S., Tranel, P. J., Riggins, C. W., McGinness, D. L., Hager, A. G., Hawkes, T., McIndoe, E. & Riechers, D. E. 2013. Distinct detoxification mechanisms confer resistance to mesotrione and atrazine in a population of waterhemp. Plant Physiol, 163, 363-77.

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