First report of glyphosate resistance in an <scp> <i>Amaranthus palmeri</i> </scp> population from Europe

The invasive weed Amaranthus palmeri is spreading throughout Spain, with Catalonia being one of the most affected regions. For this species, acetolactate synthase-inhibiting herbicide-resistant populations have been reported, and now glyphosate resistance also suspected. Glyphosate targets inhibits enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), but A. has evolved different resistant mechanisms leading to plant survival. One effective EPSPS overexpression due copy number variation (CNV). Gene copies accumulate within cassette that an extrachromosomal circular DNA displaying unique structural polymorphisms. This study aims determine response a suspected population collected from roadside investigate mechanism involved. herbicide bioassay confirmed 40% plants survived applied at 540 g a.i. ha−1. No known mutations endowing were found amongst plants, while in them (70%) specific molecular markers revealed presence cassette. All these results indicate it very likely gene CNV main mechanism. first case Europe whose introduction importation contaminated seed glyphosate-resistant Palmer amaranth Americas. poses significant danger summer crops our continent.