Quantitative genetics of growth and development in Populus. II. The partitioning of genotype × environment interaction in stem growth

Abstract

Two interspecific hybrid pedigrees of Populus trichocarpa and P. deltoides, each containing parental, F1 and F2 generations, and planted in two contrasting environments in northern Oregon, served to estimate the interactions of genotypes environments for stem growth during the first two years of growth. All three generations showed greater mean growth in the warm, high-radiation, and well-watered regime of the interior (Boardman) than in the cooler coastal conditions of Clatskanie. In the two F2 families, all stem traits displayed significant genotype environment interactions which accounted for 10 per cent of the total phenotypic variance. Genetic correlations across environments were larger for basal area and volume growth than for stem height and proportion. Genotype environment interaction variance was further partitioned into two components attributable to the heterogeneity of genetic variance between environments and the lack of genetic correlation across environments. For radial and volume growth, a large amount of genotype environment interaction was associated with the heterogeneity of genetic variance across environments. For stem height and proportion, lack of genetic correlation across environments explained more of the genotype environment interaction. The Spearman rank correlations of phenotypic means between the two environments were moderately high but significantly less than unity in most cases. Much of the growth difference in the two F2 families had a significant genetic component, with broad-sense heritabilities at each location ranging from 0.70–0.90. The implications for breeding and selection of superior poplars for these environments are discussed.