VARIANCE-COMPONENTS, HERITABILITIES AND GAIN ESTIMATES FOR GROWTH CHAMBER AND FIELD PERFORMANCE OF POPULUS-TREMULOIDES - GROWTH-PARAMETERS

Variance components, heritabilities and gain estimates are reported fo r 29 clones (five populations) of Populus tremuloides from Alberta, Ca nada, which were grown (two years) at two field sites (northern and so uthern Alberta) and in two controlled environment chambers (for 12 wee ks). Results indicated more variation at the clone-within-population l evel than the population level. There was more variation accounted for by both clone-within-population and population in the growth chamber than in the field. Caliper: clone-growth chamber: 32%, field: 22% to 7 %; caliper: population-growth chamber: 12%, field: 2%; height: clone-g rowth chamber: 7% to 27%; bud-burst: clone-growth chamber: 26%; root-t o-shoot ratio: clone-growth chamber: 17%. Broad-sense clone mean herit abilities for caliper were also lower in the field (0.56 to 0.29), tha n in the growth chambers (0.80). Heritabilities in the growth chamber were: Bud-burst = 0.72, height = 0.74, root-to-shoot ratio = 0.59. Exp ected gains, estimated based on growth chamber data, were: 9% to 38% a cross populations for bud-burst, 11% to 24% for caliper, 12% to 22% fo r final height, and 8% to 19% for root-to-shoot. This study indicates that significant improvement in traits is possible in trembling aspen with a 17% selection intensity but that care must be taken in determin ing the size of the region that will comprise the population where sel ections are made.