Effect of EPSPS gene copy number and glyphosate selection on fitness of glyphosate-resistant Bassia scoparia in the field

Charlemagne Ajoc Lim,Alan T Dyer,Prashant Jha,Vipan Kumar

doi:10.1038/s41598-021-95517-2

Abstract

The widespread evolution of glyphosate-resistant (GR) Bassia scoparia in the U.S. Great Plains poses a serious threat to the long-term sustainability of GR sugar beet. Glyphosate resistance in B. scoparia is due to an increase in the EPSPS (5-enolpyruvyl-shikimate-3-phosphate) gene copy number. The variation in EPSPS gene copies among individuals from within a single GR B. scoparia population indicated a differential response to glyphosate selection. With the continued use of glyphosate in GR sugar beet, the effect of increasing glyphosate rates (applied as single or sequential applications) on the fitness of GR B. scoparia individuals with variable EPSPS gene copies was tested under field conditions. The variation in EPSPS gene copy number and total glyphosate rate (single or sequential applications) did not influence any of the reproductive traits of GR B. scoparia, except seed production. Sequential applications of glyphosate with a total rate of 2214 g ae ha−1 or higher prevented seed production in B. scoparia plants with 2–4 (low levels of resistance) and 5–6 (moderate levels of resistance) EPSPS gene copies. Timely sequential applications of glyphosate (full recommended rates) can potentially slow down the evolution of GR B. scoparia with low to moderate levels of resistance (2–6 EPSPS gene copies), but any survivors (highly-resistant individuals with ≥ 8 EPSPS gene copies) need to be mechanically removed before flowering from GR sugar beet fields. This research warrants the need to adopt ecologically based, multi-tactic strategies to reduce exposure of B. scoparia to glyphosate in GR sugar beet.

Highlights

The widespread evolution of glyphosate-resistant (GR) Bassia scoparia in the U.S Great Plains poses a serious threat to the long-term sustainability of GR sugar beet
A differential response of B. scoparia plants with varying enolpyruvyl-shikimate-3-phosphate synthase (EPSPS) copy numbers was observed across glyphosate rates tested
In the absence of glyphosate, the EPSPS gene copy number had no effect on time to 50% flowering (P = 0.17), time to set seeds (P = 0.18), pollen viability (P = 0.23), seeds plant-1 (P = 0.94), and seed viability (P = 0.41), but had a significant effect on 1000-seed weight and seedling radicle length (P < 0.01) (Table 1)

Summary

Introduction

The widespread evolution of glyphosate-resistant (GR) Bassia scoparia in the U.S Great Plains poses a serious threat to the long-term sustainability of GR sugar beet. With the continued use of glyphosate in GR sugar beet, the effect of increasing glyphosate rates (applied as single or sequential applications) on the fitness of GR B. scoparia individuals with variable EPSPS gene copies was tested under field conditions. The variation in EPSPS gene copy number and total glyphosate rate (single or sequential applications) did not influence any of the reproductive traits of GR B. scoparia, except seed production. Sequential applications of glyphosate with a total rate of 2214 g ae ha−1 or higher prevented seed production in B. scoparia plants with 2–4 (low levels of resistance) and 5–6 (moderate levels of resistance) EPSPS gene copies. Reproductive traits Time to flowering Time to set seeds Pollen viability Seeds plant-1 1000-seed weight Seed viability Radicle length

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