EPSPS gene amplification confers glyphosate resistance in palmer amaranth from Connecticut

Authors: AULAKH, JATINDER - Connecticut Agricultural Experiment Station; KUMAR, VIPAN - Cornell University; BRUNHARO, CAIO - Pennsylvania State University; VERON, ADRIAN - Pennsylvania State University; Price, Andrew

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: A Palmer amaranth biotype (CT-Res) with resistance to glyphosate and ALS inhibitors was recently confirmed from a pumpkin field in Connecticut. However, the underlying mechanism (s) conferring glyphosate resistance in this biotype is not known. The main objectives of this research were (1) to determine the effect of plant height (10-, 20-, and 30-cm tall) on glyphosate resistance levels in CT-Res Palmer amaranth biotype, and (2) to investigate if the target-site-based mechanisms confer glyphosate resistance. To achieve these objectives, progeny seeds of CT-Res biotype after two generation of recurrent selection with glyphosate (6,720 g ae ha-1) were used. For comparison, a known glyphosate susceptible Palmer amaranth biotype from Kansas (KS-Sus) was included. Results from whole plant dose-response studies revealed that CT-Res Palmer amaranth biotype had 69-, 64-, and 54-fold resistance to glyphosate as compared to KS-Sus biotype when treated at 10-, 20-, and 30-cm tall, respectively. Sequence analysis of the EPSPS gene revealed no point mutations at the Pro106 and Thr102 residues in the CT-Res Palmer amaranth biotype. The qPCR analysis revealed that CT-Res Palmer amaranth biotype had 25 to 103 relative copies of the EPSPS gene compared to KS-Sus biotype with only 1 EPSPS gene copy. In conclusion, all these results suggest that EPSPS gene amplification endows high level of glyphosate resistance in GR Palmer amaranth biotype from Connecticut. Growers should adopt effective alternative PRE and POST herbicides in conjunction with other cultural, mechanical, or precision agricultural technologies to control GR Palmer amaranth.

Technical Abstract: A Palmer amaranth biotype (CT-Res) with resistance to glyphosate and ALS inhibitors was recently confirmed from a pumpkin field in Connecticut. However, the underlying mechanism (s) conferring glyphosate resistance in this biotype is not known. The main objectives of this research were (1) to determine the effect of plant height (10-, 20-, and 30-cm tall) on glyphosate resistance levels in CT-Res Palmer amaranth biotype, and (2) to investigate if the target-site-based mechanisms confer glyphosate resistance. To achieve these objectives, progeny seeds of CT-Res biotype after two generation of recurrent selection with glyphosate (6,720 g ae ha-1) were used. Similarly, a known glyphosate susceptible Palmer amaranth biotype from Kansas (KS-Sus) was included. Results from whole plant dose-response studies revealed that CT-Res Palmer amaranth biotype had 69-, 64-, and 54-fold resistance to glyphosate as compared to KS-Sus biotype when treated at 10-, 20-, and 30-cm tall, respectively. Sequence analysis of the EPSPS gene revealed no point mutations at the Pro106 and Thr102 residues in the CT-Res Palmer amaranth biotype. The qPCR analysis revealed that CT-Res Palmer amaranth biotype had 25 to 103 relative copies of the EPSPS gene compared to KS-Sus biotype with only 1 EPSPS gene copy. In conclusion, all these results suggest that EPSPS gene amplification endows high level of glyphosate resistance in GR Palmer amaranth biotype from Connecticut. Growers should adopt effective alternative PRE and POST herbicides in conjunction with other cultural, mechanical, or precision agricultural technologies to control GR Palmer amaranth.