In multi-species swards, the genetic structure of populations of heterogeneous outbreeding
species is likely to change over time, potentially affecting inter-species population dynamics.
In this study, mixtures of outbreeding forage crops were established in swards, and periodically
defoliated by cutting or grazing for two years. Changes in population structure varied from
species to species. White clover showed significant genetic change over two years, while red
clover did not. For perennial ryegrass, a sub group in the initial population exhibiting unique
alleles was no longer present two years later. Key genes associated with stress tolerance and
flowering time varied significantly with these changes in population structure.