MULTITRAIT RESPONSE TO SELECTION IN LOLIUM-PERENNE L (PERENNIAL RYEGRASS) POPULATIONS

Genetic variation for growth, quality and persistency characteristics was assessed in six breeding populations of perennial ryegrass. Respon se to multitrait selection was predicted in each population using a se lection index based on 10 traits. Predicted response was compared with that observed after one generation of half-sib family selection based on breeder's preference. There was generally good agreement between p redicted and observed response and it was possible to use predictions to identify populations with good potential to meet breeding objective s. For two of the breeding populations, observed selection responses a fter three generations of recurrent selection and in the progeny of su rvivors from cut and grazed plots were used to estimate selection pres sures on individual traits. It appears that greater selection pressure s are imposed on heading date and summer regrowth under grazing compar ed with cutting managements. The results illustrate the value of a mul tivariate approach in predicting the progress of breeding programmes a nd in identifying traits most affected by natural selection pressures.