Changes in plant morphological expression in 12 perennial ryegrass cultivars following frequent and infrequent cutting management

SUMMARY Perennial ryegrass (Lolium perenne L.) cultivars are out-breeding populations of differing phenotypes, potentially allowing for directional selection to occur after sowing. To investigate this, the morphology of individual space plants (i.e. isolated plants sown at 0·75 m row spaces) grown from tillers extracted from single-cultivar swards subjected to frequent cutting (FC) or infrequent cutting (IC) for 5 years (aged accessions) were compared with plants grown from seed (seed accessions). The study examined 12 cultivars, creating 36 'accessions' of 80 plants in each. These plants were examined for 23 morphological measurements to test for and classify directional selection in perennial ryegrass swards. A high degree of separation was achieved between the 12 seed accessions, validating the discriminating power of the experiment. Changes in morphological expression of plants taken from swards indicated selection in favour of particular morphological ideotypes. This directional selection was identified in 10 of the accessions subjected to FC and eight subjected to IC management. Emergence natural height (plant undisturbed height at inflorescence emergence) and plant volume (emergence width × emergence natural height) were the characters modified most between seed and aged accessions. The magnitude of these morphological changes varied between cultivars. Glencar had the greatest number of morphological characters exhibiting directional selection under frequent cutting, whereas Greengold had the greatest number exhibiting directional selection under infrequent cutting. The plants grown from aged swards were also smaller than the seed accessions in all characters, raising the possibility that they may also be less productive. The present study showed that sward management can cause and influence directional selection of plants from within the morphological range of expression within perennial ryegrass cultivars.