Increased Activity of 5-Enolpyruvylshikimate-3-phosphate Synthase (EPSPS) Enzyme Describe the Natural Tolerance of Vulpia myuros to Glyphosate in Comparison with Apera spica-venti

Zelalem Eshetu Bekalu,Solvejg Kopp Mathiassen,Henrik Brinch-Pedersen,Muhammad Javaid Akhter,Per Kudsk

doi:10.3390/agriculture11080725

Zelalem Eshetu Bekalu, Solvejg Kopp Mathiassen + Show 3 more

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https://doi.org/10.3390/agriculture11080725

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Journal: Agriculture	Publication Date: Jul 30, 2021
Citations: 2	License type: CC BY 4.0

Affiliation: Aarhus University

Abstract

Rattail fescue (Vulpia myuros (L.) C.C. Gmel.) is a self-pollinating winter annual grassy weed of winter annual crops. The problems with V. myuros are mostly associated with no-till cropping systems where glyphosate application before sowing or emergence of the crop is the most important control measure. Ineffective V. myuros control has been reported following glyphosate applications. Experiments were performed to study the effectiveness of glyphosate on V. myuros, and determine the causes of the lower performance of glyphosate on V. myuros compared to other grass weeds. Estimated GR50 values demonstrated that V. myuros was less susceptible to glyphosate than Apera spica-venti regardless of the growth stage. Within each species, glyphosate efficacy at different growth stages was closely related to spray retention. However, the low susceptibility to glyphosate in V. myuros was not caused by lower retention as previously suggested. A significantly lower shikimic acid accumulation in V. myuros compared to A. spica-venti was associated with a higher activity of the EPSPS enzyme in V. myuros. Nevertheless, the relative responses in EPSPS activity to different glyphosate concentrations were similar in the two grass species, which indicate that EPSPS from V. myuros is as susceptible to glyphosate as EPSPS from A. spica-venti suggesting no alternation in the binding site of EPSPS. The results from the current study indicate that V. myuros is less susceptible to glyphosate compared to A. spica-venti, and the low susceptibility of V. myuros is caused by an increased EPSPS enzyme activity.

Highlights

The tolerance index (TI), i.e., GR50 of V. myuros relative to GR50 of A. spica-venti indicated that V. myuros required 2.8, 2.0 and 4.0 times higher doses than A. spica-venti for a 50% reduction of biomass at BBCH 11, BBCH 13 and BBCH 21, respectively in Experiment 1
The current study confirmed that V. myuros is more tolerant than other grass species to glyphosate as it is to other herbicide modes of action and it showed that the tolerance is not attributed to low spray retention as previously anticipated
The EPSPS activity in V. myuros was elevated compared to A. spica-venti and could explain the lower accumulation of shikimic acid in V. myuros and the observed difference in the susceptibility between the two grass weed species

Summary

Introduction

Rattail fescue (Vulpia myuros (L.) C.C. Gmel.) is considered a problematic weed in Northern European countries [1]. Since first reported in Denmark in 1990, areas infested with V. myuros have significantly increased [2]. V. myuros was primarily found in grass seed crops, in particular red fescue; with increasing adoption of no-till practices and repeated cropping of winter cereals, V. myuros is considered a common weed in winter cereal crops as well [3,4]. Vulpia myuros is a winter annual grass weed with a life cycle very similar to winter wheat [5]. Vulpia myuros is a prolific seed producer and can form a large seed-bank in a single season under poor weed management scenarios [6].

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