Evolution, growth and phenology of Phalaris minor biotypes resistant to ACCase-inhibiting herbicides in Mexico

Background: Herbicide application to control weeds can promote a rapid selection of resistant phenotypes in small geographic areas. Also, in areas with a spatial heterogeneous management, resistance may evolve independently, promoting local adaptation in weeds. In the mexican region known as "El Bajio," 100,000 ha are cultivated with wheat, and the weed Phalaris minor, resistant to ACCase-inhibiting herbicides is commonly present. Question: We aim to identify the population structure of two genes in four different P. minor biotypes from "El Bajio" and to determine their association with phenology and plant growth differences (biomass and seed yield) that may contribute to survival in the agricultural environment. Studied species: Phalaris minor Retz. Study site and years of study: The study was carried out at a greenhouse and at the molecular biology laboratory of the Colegio de Postgraduados, during 2013 and 2014. Methods: The diversity of the psbA gene and the sequence of two ACCase gene fragments as well as phenology, growth and biomass allocation were evaluated. Results: Results indicated different polymorphism levels for the two genes. There were no differences in the psbA gene between biotypes, although the ACCase gene exhibited high polymorphism level. In addition, each biotype showed differences in phenology, biomass accumulation and fecundity. Conclusions: The ACCase-inhibiting herbicide resistance in "El Bajio" region might be a resistance hotspot leading to the local adaptation of weeds.