Glyphosate resistance in Amaranthus palmeri populations in Europe
Amaranthus palmeri (Amaranthaceae - EPPO A2 List) is a dioecious summer annual species native to North America. In its native range, it is a weed in agricultural fields and disturbed habitats. It has a high fecundity and a long-lived seed bank, which make management of the species difficult. In the EPPO region, it is established in a few countries and transient in others. In Spain, A. palmeri is invasive especially in Catalonia. Herbicide resistance has been reported in populations of A. palmeri (see EPPO RS 2021/095 and EPPO RS 2022/158). However, this is the first-time that glyphosate resistant populations have been reported in the EPPO region. In 2021, mature seeds were collected from a suspected glyphosate resistant population near Tarragona harbour in Spain. A. palmeri seedlings were grown in controlled, replicated conditions and glyphosate was applied at the standard field dose rate. A population of A. palmeri known to be susceptible to glyphosate was treated in the same way. All susceptible plants died whereas 10 out of the 25 treated plants collected from Tarragona harbour survived. The dose experiment and subsequent DNA analysis of the resistant plants indicate that the Tarragona harbour population is glyphosate resistant, and it is likely that the EPSPS gene copy number variation is the main resistance mechanism. It is likely that glyphosate resistance seed has been introduced into the EPPO region via the importation of contaminated seed. Further studies are needed to evaluate how widespread glyphosate resistant populations are in the EPPO region.
Sources
Manicardi A, Milani A, Scarabel L, Mora G, Recasens J, Llenes JM, Montull JM, Torra J (2023) First report of glyphosate resistance in an Amaranthus palmeri population in Europe. Weed Research (early view). https://doi.org/10.1111/wre.12579