Description

Glyphosate is best known as the active ingredient in Roundup-branded herbicides, and the herbicide used with “Roundup Ready” genetically modified organisms (GMOs). Due to long-term use of the herbicide, glyphosate (Group 9) resistance has evolved in many weeds including kochia (Bassia scoparia). 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 increase as the number of EPSPS genomic copies increases. The effect of the additional copies becomes additive and additional copies confer higher levels of resistance (Gaines et al., 2016; Godar et al. 2015; Martin et al. 2020).

NAGC validated a DNA-based test for estimating EPSPS gene copy numbers by upgrading the published SYBR qPCR tests (e.g., Gaines et al. 2016) into a single closed-tube probe qPCR assay. The test and estimated number of EPSPS gene copies for leaf samples is normalized to that of a single copy genetic marker (carbamoyl phosphate synthetase; CPS) within the genome. This test provides faster preliminary results to growers on the glyphosate resistance potential of kochia in their fields. Additionally, this test provides weed scientists with a rapid method to screen for herbicide resistance during their experiments in the greenhouse and field.

This project was funded by the North Dakota Corn Utilization Council, North Dakota Soybean Council, and North Dakota Department of Agriculture.

References

Godar, A. S., Stahlman, P. W., Jugulam, M., & Dille, J. A. (2015). Glyphosate-resistant kochia (Kochia scoparia) in Kansas: EPSPS gene copy number in relation to resistance levels. Weed Science, 63(3), 587-595.

Gaines, T. A., Barker, A. L., Patterson, E. L., Westra, P., Westra, E. P., Wilson, R. G., … & Kniss, A. R. (2016). EPSPS gene copy number and whole-plant glyphosate resistance level in Kochia scoparia. PLoS One, 11(12), e0168295.

Martin, S. L., Benedict, L., Wei, W., Sauder, C. A., Beckie, H. J., & Hall, L. M. (2020). High gene flow maintains genetic diversity following selection for high EPSPS copy number in the weed kochia (Amaranthaceae). Scientific Reports, 10(1), 18864.