Multiple mutations in the EPSPS and ALS genes of Amaranthus hybridus underlie resistance to glyphosate and ALS inhibitors release_aegljnuyyjhudkycembwo27lqa

Abstract

<jats:title>Abstract</jats:title> <jats:italic>Amaranthus hybridus</jats:italic> 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 <jats:italic>A. hybridus</jats:italic> population. In the case of <jats:italic>EPSPS</jats:italic>, the triple amino acid substitution TAP-IVS was found. In addition, MR2 plants also showed increased <jats:italic>EPSPS</jats:italic> gene expression compared to susceptible plants. A Ser653Asn substitution was found in the <jats:italic>ALS</jats:italic> 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 <jats:italic>ALS</jats:italic> gene. This is the first report worldwide of the target site resistance mechanisms to glyphosate and ALS inhibitors in multiple herbicide resistance <jats:italic>Amaranthus hybridus</jats:italic>.
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