Herbicide resistant Amaranthus palmeri populations in Italy and Spain
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. Some populations of A. palmeri are known to be resistant to acetolactate synthase (ALS) inhibitors, making them resistant to herbicides. Twelve populations of A. palmeri were sampled (four from Italy, seven from Spain and one from North Carolina (USA)), and seed was collected from 30 mature female plants at each site. Bioassay studies were conducted on each population to determine their sensitivity to two herbicides: thifensulfuron-methyl (sulfonylurea) and imazamox (imidazolinone). Those plants that survived herbicide application had genomic DNA extracted and amplified to detect mutations. The results showed that seven populations from Spain and one from Italy have evolved resistance to ALS. It is likely that herbicide resistance did not evolve in the EPPO region but rather in the native range of A. palmeri. Herbicide resistant plants have entered the EPPO region via contaminant of seed or grain. ALS resistance has spread within the EPPO region, over short and long distances by seed dispersal. The implementation of management techniques to contain the spread and establishment of A. palmeri is recommended in countries where it occurs.
Sources
Manicardi A, Scarabel L, Lienes JM, Montull JM, Osuna MD, Farré JT, Milani A (2023) Genetic basis and origin of resistance to acetolactate synthase inhibitors in Amaranthus palmeri from Spain and Italy. Pest Management Science. https://doi.org/10.1002/ps.7690