Breeding perennial ryegrass varieties with an improved combining ability with white clover

White clover varieties, bred in Europe, are mostly evaluated in grass swards. Perennial ryegrass varieties, on the other hand, except in some rare scientific experiments, are bred in monocultures receiving high nitrogen inputs. Hence, the resulting varieties are not necessarily persistent and productive in mixtures with clover. As the transition from grass to grass-clover is essential to increase the sustainability of European agriculture, we conducted an experiment to find out whether it would be best to breed dedicated perennial ryegrass varieties for this purpose. In a three-year field trial, eighteen perennial ryegrass populations were either sown as monocultures, receiving 300 kg N ha–1 year–1 or in a mixture with white clover receiving 150 kg N ha–1 year–1 under conservation management. Although no significant yield interactions were found between population and clover presence, contrasting reactions of the populations were found. For example, the yield of population 11, when expressed relative to the average of the eighteen populations for 2021 and 2022, was 4% and 5%, respectively, higher in combination with clover, but 2% and 7% respectively, lower in monoculture. Strengthened by these results, an important part of our actual breeding effort in perennial ryegrass breeding is in the development of varieties with a good combining ability with white clover.