Glyphosate resistance in common ragweed (Ambrosia artemisiifolia L.)from Mississippi, USA

Authors: Nandula, Vijay; TEHRANCHIAN, PARSA - University Of California; BOND, JASON - University Of Arkansas; NORSWORTHY, JASON - Delta Research & Extension Center; EUBANK, THOMAS - Mycogen Seed Company

Submitted to: Weed Biology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/25/2016
Publication Date: 4/20/2017
Citation: Nandula, V.K., Tehranchian, P., Bond, J.A., Norsworthy, J.K., Eubank, T.W. 2017. Glyphosate resistance in common ragweed (Ambrosia artemisiifolia L.)from Mississippi, USA. Weed Biology and Management. 17:45-53.

Interpretive Summary: Glyphosate is one of the most commonly used broad-spectrum herbicides over the last 40 years. Due to widespread adoption of glyphosate-resistant (GR) crop technology, especially, corn, cotton, and soybean, several weed species in agronomic situations, including common ragweed, have developed resistance to this herbicide. Scientists from the Crop Production Systems Research Unit of USDA-ARS, University of California, Davis, University of Arkansas, Mississippi State University, and Dow AgroSciences conducted greenhouse and laboratory research to confirm and characterize magnitude and mechanism of glyphosate resistance in two GR common ragweed biotypes from Mississippi, USA. A susceptible biotype was included for comparison. ED50 (effective glyphosate dose to reduce growth of treated plants by 50%) values for GR1, GR2, and glyphosate-susceptible (GS) biotypes were 0.58, 0.46, and 0.11 kg ae ha-1, respectively, indicating that GR1 and GR2 were 5- and 4-fold, respectively, more resistant to glyphosate than GS. 14C-glyphosate absorption and translocation did not indicate any difference in uptake between the biotypes, but the GR1 and GR2 biotypes translocated more 14C-glyphosate compared to the GS biotype. This difference in translocation within resistant biotypes is unique. There was no amino-acid substitution at the codon 106 detected by 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene sequence analysis of the resistant and susceptible biotypes. These results greatly add to the knowledge of glyphosate resistance mechanisms in common ragweed of which very less is understood.

Technical Abstract: Glyphosate is one of the most commonly used broad-spectrum herbicides over the last 40 years. Due to widespread adoption of glyphosate-resistant (GR) crop technology, especially, corn, cotton, and soybean, several weed species in agronomic situations have developed resistance to this herbicide. Research was conducted to confirm and characterize magnitude and mechanism of glyphosate resistance in two GR common ragweed biotypes from Mississippi, USA. A susceptible biotype was included for comparison. ED50 (effective glyphosate dose to reduce growth of treated plants by 50%) values for GR1, GR2, and glyphosate-susceptible (GS) biotypes were 0.58, 0.46, and 0.11 kg ae ha-1, respectively, indicating that GR1 and GR2 were 5- and 4-fold, respectively, more resistant to glyphosate than GS. 14C-glyphosate absorption and translocation did not indicate any difference in uptake between the biotypes, but the GR1 and GR2 biotypes translocated more 14C-glyphosate compared to the GS biotype. This difference in translocation within resistant biotypes is unique. There was no amino-acid substitution at the codon 106 detected by 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene sequence analysis of the resistant and susceptible biotypes. Therefore, the mechanism of resistance to glyphosate in common ragweed biotypes from Mississippi is not due to a target site mutation or reduced absorption and/or translocation of glyphosate.