Ryegrass ( Lolium multiflorum Lam.) is an important forage and suffers negative interference from weeds, like annual bluegrass ( Poa annua L.). The competition of annual bluegrass with ryegrass can interfere with crop growth and reduce the amount of forage for animal feed. We aimed to evaluate the interference of annual bluegrass in ryegrass crops through the differentiation of niche and establishment. Two experiments were carried out testing different competition strata (shoot, root, and both) and ryegrass establishment with or after annual bluegrass, with increasing populations of annual bluegrass (0, 35, 139, 279, 419 plants m ^–2). The variables were plant height, height length of the root system, stem diameter, and fresh weight of shoot and root systems of ryegrass. The negative interference of growing populations of annual bluegrass occurred when in competition for the shoot and root systems of ryegrass. The fresh weight of shoots and roots were impacted when competing for the same strata. Ryegrass, established after the population of annual bluegrass, showed less competitive capacity. The negative interference of annual bluegrass in ryegrass is greater when the plants fully compete for the resources of the environment, and when the ryegrass establishes after the competitor.

Poa annua L. is the only non−native vascular plant that was successfully established in the maritime Antarctic. This project aimed to determine the amount of genetic and epigenetic variation within and between two populations of P. annua , one from South Shetland Is. (Antarctic) and the other one from Central Europe. We applied two AFLP marker systems, using endonucleases that recognised the same restriction site but differed in their sensitivity towards methylation. The Antarctic population differed from the Polish one both at the genetic and epigenetic levels. Genetic variability in the Antarctic population was lower than in the Polish one. Some loci in the Antarctic population showed signs of selection. The difference between Polish and Antarctic populations might be due to a weak bottleneck effect followed by population expansion. Using only epigenetic markers, the Ant − arctic population exhibited increased variation level compared to the Polish one. These may have resulted from plastic responses to environmental factors and could be associated with survival in extreme conditions.