High gene flow promotes the genetic homogeneity of arable weed populations at the landscape level

To determine whether weed populations growing in neighbouring fields were genetically Isolated, we investigated the genetic contamination of Alopecurus myosuroides populations in organic fields by populations in conventional fields Herbicide resistance was used as a marker for gene flow to organic populations, which are not under herbicide selective pressure Organic fields contained on average 74 5% herbicide-resistant plants (80 1% in conventional fields) Identical resistance alleles were found in neighbouring organic and conventional fields AFLP analysts revealed that populations from organic and conventional fields had similar neutral genetic diversity Massive pollen flow from conventional fields is likely chiefly responsible for the genetic makeup of A myosuroides populations from organic fields Using a demo-genetic model, we propose that demographic collapses of populations due to effective weed control enhance gene flow towards these populations Fields with a low weed density could act as 'genetic sinks' that would facilitate the diffusion of genes from neighbouring, dense weed populations Populations of allogamous wind-pollinated weed species like A myosuroides occurring in neighbouring fields are therefore clearly not Independent units Adaptive evolution and management of such weeds should thus be considered on a scale broader than the field