# Resistance to Amino Acid Biosynthesis Inhibiting-Herbicides in Amaranthus palmeri Populations from Aragon (Spain)

## TL;DR

This study examines herbicide resistance in Amaranthus palmeri weed populations from Aragon, Spain, finding genetic variations that confer resistance to specific herbicides.

## Contribution

The study identifies new resistance mutations and gene amplifications in A. palmeri populations from Aragon, contributing to understanding herbicide resistance spread in Spain.

## Key findings

- The Bujaraloz population showed moderate glyphosate resistance due to EPSPS gene amplification.
- Three populations had ALS gene mutations (Trp574Leu and Pro197Thr) conferring herbicide resistance.
- High genetic variability was observed, with no multiple resistance detected across populations.

## Abstract

Amaranthus palmeri is a highly problematic agricultural weed due to its rapid growth, high seed production, and strong tendency to develop herbicide resistance. In Spain, the initial colonization of A. palmeri began in 2007, when populations were detected at various locations in the province of Lleida (Catalonia). Since then, new infestations have been reported in other regions of the country, primarily infesting maize fields. Although resistance to glyphosate or to acetolactate synthase (ALS) inhibitors has been documented in several populations from Catalonia and Extremadura, little is known about the resistance profile of populations from Aragon. The main objective of this study was to characterize the putative resistance of five populations from Aragon to 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibitors (glyphosate) and ALS inhibitors (nicosulfuron and imazamox). Sensitivity to both mechanisms of action was measured by root growth in vertical plates and shikimate accumulation for glyphosate. Target-site resistance was evaluated by analyzing EPSPS and ALS gene copy numbers and ALS gene mutations. The populations showed high variability, with no multiple resistance detected. The Bujaraloz population showed moderate resistance to glyphosate due to EPSPS gene amplification. In three populations, mutations in the ALS gene conferring resistance were detected. The Trp574Leu mutation was detected in approximately half of the individuals from the Albelda, Tamarite de Litera, and Caspe populations. In the latter, the Pro197Thr mutation was also present. This study reveals significant genetic variability within each population and provides evidence for the spread of herbicide resistance across different regions of Spain.