COMPARISON OF PREDICTED AND OBSERVED RESPONSE TO SELECTION IN 2 BREEDING POPULATIONS OF PERENNIAL RYEGRASS

To predict any genetic response to selection, two breeding populations of perennial ryegrass, consisting of half-sib families, were evaluate d as spaced plants from 1987 to 1989 for several agronomical traits. I n each population, the best plants selected through a multitrait Smith and Hazel's index were planted in a polycross to produce the second g eneration half-sib families. Both generations were evaluated together from 1991 to 1993 as spaced plants. The difference between generations was the observed genetic response, which was compared to that predict ed. Rust tolerance, aftermath heading and persistence were significant ly improved in both populations. In trial plots used to assess the yie ld, no effect of mass selection was noticed. Thus, it is concluded tha t mass selection failed to increase productivity but produced some imp rovements in disease tolerance and aftermath heading.