Journal Article

Glyphosate resistance and EPSPS gene amplification confirmed in a waterhemp (Amaranthus tuberculatus) biotype from Connecticut

Jhala, Amit J., Westrick, Nathaniel, Aulakh, Jatinder S., Price, Andrew J., Kumar, Vipan

2025

Overview

Waterhemp (Amaranthus tuberculatus) is an economically important broadleaf weed that threatens corn and soybean production across the United States. A waterhemp biotype (CT_Res [resistant biotype from Connecticut]) surviving multiple glyphosate applications was identified from a corn field in Connecticut (CT). Greenhouse and laboratory studies were conducted to (1) confirm glyphosate resistance in CT_Res waterhemp biotype and (2) investigate if the glyphosate resistance in CT_Res biotype is due to target‐site‐based mechanism. Dose‐response studies indicated that CT_Res biotype was 5.8‐fold more resistant to glyphosate compared to a known susceptible biotype (NE_Sus) from Nebraska. No point mutation was detected at Pro102 or Thr106 positions in the EPSPS gene of the CT_Res biotype. The quantitative polymerase chain reaction assays revealed that one of the three CT_Res waterhemp plants had 3.5‐fold higher EPSPS gene copy number (relative to the housekeeping CPS gene), whereas the other two plants did not reveal EPSPS gene amplification. Obviously, the EPSPS gene amplification partially explains glyphosate resistance in newly identified glyphosate‐resistant waterhemp biotype from CT, indicating that alternative mechanisms might exist. This research reports the first case of glyphosate resistance and EPSPS gene amplification in waterhemp from Connecticut and highlights the need for adoption of diversified weed control strategies to prevent its further spread. Core Ideas A suspected waterhemp biotype from Connecticut was characterized for glyphosate resistance and target‐site based mechanism. Connecticut waterhemp biotype exhibited 5.8‐fold resistance to glyphosate compared to a susceptible biotype from Nebraska. Sequence analysis of the EPSPS gene revealed no mutation at Pro102 or Thr106 positions in Connecticut waterhemp biotype. One of the three glyphosate‐resistant waterhemp plants from Connecticut had 3.5‐fold higher EPSPS gene copy number. Plain Language Summary Waterhemp is one of the most troublesome weed species in the US Midwest. In recent years, waterhemp biotypes are also identified in northeastern United States, including Connecticut and New York. This research was aimed to confirm the presence of glyphosate resistance in a waterhemp biotype collected from a corn field in Connecticut and investigate if the glyphosate resistance was due to target‐site‐based mechanism. Greenhouse studies concluded that waterhemp biotype from Connecticut was 5.8 times more resistant to glyphosate when compared with a known glyphosate‐susceptible biotype from Nebraska. Furthermore, one out of three glyphosate‐resistant waterhemp plants showed 3.5 times higher copies of target gene (EPSPS). Altogether, these results confirm the first report of glyphosate resistance in recently identified waterhemp biotype from Connecticut. Growers need to be vigilant and should adopt diversified weed control strategies to prevent its further spread.

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Amaranthus tuberculatus / Copy number / Corn / CPS gene / Crop production / Economic importance / EPSPS gene / Gene amplification / Glyphosate / Herbicide resistance / Point mutation / Polymerase chain reaction / Soybeans / Weed control / Weeds