Résumé
Germplasm from perennial ryegrass (Lolium perenne L.) natural populations is useful for breeding because of its adaptation to a wide range of climates. We identified adaptive loci in perennial ryegrass and their association with seasonal growth traits and climatic gradients. Adaptive loci associated with autumn growth under cold winters and summer growth under dry and long summers were common to only a limited extent, pointing to a moderate trade-off along the winter-summer stress gradient due to antagonistic pleiotropy. Meanwhile, most adaptive loci were found specific to one type of stress or the other. It should therefore be possible to combine adaptation to winter and summer stresses by genetic recombination. This would be particularly useful in view of foreseen increasing climate variability due to climate change in Europe. On the other hand, the climatic distribution models of adaptive allele frequencies revealed a risk of local extinction in regions with much drier and warmer summers in the future such as the Iberian Peninsula and southern France.