Implications of selection history on genetic architecture of growth, form, and wood-quality traits in Pinus radiata

Clonal trials of Pinus radiata D. Don (radiata pine), representing two populations (or breeds), one selected for growth and form (GF) and the other selected for high wood density as well as growth and form (HD), were replicated on two low-altitude New Zealand sites: Tarawera (pumice soil, 38 degrees 08'S) and Woodhill (coastal dune, 36 degrees 42'S). The GF material comprised 33 pair-crosses (19 parents) x 10 clones, and the HD material comprised 19 single-pair crosses (35 parents) x 10 clones, with six ramets per clone per site. Diameter (DBII), two tree-form variables, and needle retention (NRA) were assessed 8 years after planting, and wood density (DEN), acoustic velocity, and collapse were assessed 9 years after planting. The site differences were generally expressed more strongly in the GF population. Estimated genetic parameters were mostly similar for the two breeds, except that genotypic correlation between DBH and DEN was apparently zero in the HD population. Estimated broad-sense heritabilities (H-2) were generally markedly higher than narrow-sense heritability estimates (h(2)), except with DEN. Estimated between-site type-B clonal genotypic correlations were generally high (>0.8) for wood properties. Overall, DBH showed adverse genetic correlations with wood properties. The Elite/Breed strategy appeared to be helpful in combating adverse genetic correlations.