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Accepted manuscript

Dose response, shikimate accumulation, and 14C-glyphosate uptake and movement in Palmer amaranth (Amaranthus palmeri) biotypes collected 15 years apart

Published online by Cambridge University Press:  23 February 2026

Pedro Augusto Silva Martins
Affiliation:
Research Scholar, Department of Crop and Soil Sciences, University of Georgia, Tifton, GA, USA
Heytor L. Martins
Affiliation:
Ph.D. candidate, Department of Biology, Sao Paulo State University, Jaboticabal, SP, Brazil
Samantha J. Bowen
Affiliation:
Master’s student, Department of Crop and Soil Sciences, University of Georgia, Tifton, GA, USA
Kayla M. Eason
Affiliation:
Weed Scientist, Southeast Watershed Research, USDA ARS, Tifton, GA, USA
Pedro Luis da C.A. Alves
Affiliation:
Professor, Department of Biology, Sao Paulo State University, Jaboticabal, SP, Brazil
Timothy L. Grey
Affiliation:
Professor, Department of Crop and Soil Sciences, University of Georgia, Tifton, GA, USA
Juliana de S. Rodrigues*
Affiliation:
Post-Doctoral Research Associate, Department of Crop and Soil Sciences, University of Georgia, Tifton, GA, USA.
*
Author for correspondence: Juliana de Souza Rodrigues; Email: juliana.souzar@uga.edu
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Abstract

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Palmer amaranth (Amaranthus palmeri S. Watson) is one of the most problematic weeds in U.S. agriculture, capable of rapidly adapting to environmental and management pressures. This study assessed temporal changes in glyphosate response in A. palmeri by comparing ED50 values, shikimic acid accumulation, and 14C-glyphosate absorption and translocation in four biotypes collected from two Georgia fields, Jones (J) and Little Jones (LJ), in 2008 and 2023. Glyphosate ED50 increased 9-fold (J08 vs. J23) and 25-fold (LJ08 vs. LJ23), indicating a marked reduction in glyphosate sensitivity between collection periods. Shikimic acid accumulation increased with glyphosate dose in all biotypes but remained substantially lower in biotypes collected in 2023, indicating reduced EPSPS inhibition. Radiolabeled assays revealed differences in early uptake, with populations collected in 2023 reaching near maximum absorption more rapidly, as reflected by shorter times to 95 percent absorption (A95), although total absorption continued to increase across all biotypes through 48 hours after treatment. Translocation patterns varied only slightly among biotypes, suggesting that changes in glyphosate response are associated more closely with altered uptake kinetics and EPSPS related mechanisms than with major reductions in systemic movement. These results demonstrate a temporal shift in glyphosate response in Georgia A. palmeri populations and highlight the importance of integrating kinetic analyses with traditional resistance metrics.

Information

Type
Research Article
Creative Commons
Creative Common License - CCCreative Common License - BYCreative Common License - NCCreative Common License - ND
This is an Open Access article, distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives licence (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is unaltered and is properly cited. The written permission of Cambridge University Press must be obtained for commercial re-use or in order to create a derivative work.
Copyright
© The Author(s), 2026. Published by Cambridge University Press on behalf of Weed Science Society of America