Gains in annual DMY from forage grass breeding
during the last 50 years have varied more between
locations than species (Table 1). The highest gains of
4–6% per decade have been made in north-western
Europe for perennial ryegrass, in southern France for
Italian ryegrass and in Italy for tall fescue and cocksfoot.
In the USA very little progress has been made
in improving the annual DMY of either cocksfoot or
smooth bromegrass.
Differences among ryegrass varieties in annual
DMY are usually greater in the second and third harvest
years than in the first harvest year, indicating that
improvedpersistency hascontributed to the gains.Very
few routine variety trials, or experiments specifically
designed to test gains from breeding, have been extended
beyond 3 full harvest years. The effect of improved
persistency on DMY is highly dependent on