Multiple mutations in the EPSPS and ALS genes of Amaranthus hybridus underlie resistance to glyphosate and ALS inhibitors

José G Vazquez-Garcia,Maria J García,Candelario Palma-Bautista,Antonia M Rojano-Delgado,Rafael De Prado,María D Osuna,Joel Torra

doi:10.1038/s41598-020-74430-0

José G Vazquez-Garcia, Maria J García + Show 5 more

Open Access

https://doi.org/10.1038/s41598-020-74430-0

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Journal: Scientific Reports	Publication Date: Oct 19, 2020
Citations: 17	License type: open-access

Affiliation: University of Córdoba, University of Lleida

Abstract

Amaranthus hybridus is one of the main weed species in Córdoba, Argentina. Until recently, this weed was effectively controlled with recurrent use of glyphosate. However, a population exhibiting multiple resistance (MR2) to glyphosate and imazamox appeared in a glyphosate resistant (GR) soybean field, with levels of resistance up to 93 and 38-fold higher to glyphosate and imazamox, respectively compared to the susceptible (S) population. In addition to imidazolinones, MR2 plants showed high resistance levels to sulfonylamino-carbonyl (thio) benzoates and moderate resistance to sulfonylureas and triazolopyrimidines. Multiple amino acid substitutions were found in both target genes, acetolactate synthase (ALS) and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), responsible for conferring high herbicides resistance levels in this A. hybridus population. In the case of EPSPS, the triple amino acid substitution TAP-IVS was found. In addition, MR2 plants also showed increased EPSPS gene expression compared to susceptible plants. A Ser653Asn substitution was found in the ALS sequence of MR2, explaining the pattern of cross-resistance to the ALS-inhibitor herbicide families found at the ALS enzyme activity level. No other mutations were found in other conserved domains of the ALS gene. This is the first report worldwide of the target site resistance mechanisms to glyphosate and ALS inhibitors in multiple herbicide resistance Amaranthus hybridus.

Highlights

Triazine- and dinitroaniline-resistant weeds that evolved in the 1970s and 1980s were controlled by addition or replacement with acetolactate synthase (ALS) and acetyl-coenzyme A carboxylase (ACCase) inhibitors in the 1980s and 1990s
Mature seeds of an A. hybridus population suspected of having multiple resistance (MR) to imazamox and glyphosate were collected from 25 plants in a soybean field (RR) that had been treated with IMI herbicides and glyphosate for 20 years in an area of the campus of the University of Córdoba (Argentina)
Multiple resistance to glyphosate and ALS inhibitors in the A. hybridus population from Córdoba, Argentina, has been studied and characterized to decipher the target-site resistance (TSR) mechanism underlying the high resistance levels shown for the first time

Summary

Introduction

Triazine- and dinitroaniline-resistant weeds that evolved in the 1970s and 1980s were controlled by addition or replacement with acetolactate synthase (ALS) and acetyl-coenzyme A carboxylase (ACCase) inhibitors in the 1980s and 1990s. With the introduction of soybean in South America, farmers used IMI herbicides (imidazolinones) as their first chemical option in pre-planting and post-emergence of soybean This high selection pressure led to the emergence of ALS-resistant populations in the late 1990s. Farmers in South America quickly adopted technology packages for GR (glyphosate resistant) crops, mainly soybeans and corn. A triple amino acid substitution in the conserved region of the EPSPS gene (95LFLGNAGTAMRPL107), involving Thr102Ile, Ala103Val and Pro106Ser, has been very recently described as the sole mechanism responsible for a high level of resistance in two A. hybridus populations from Córdoba and Santa Fe, Argentina[16,17]

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