Analyses of Genotypic Variation in White Poplar Clones at Four Sites in China

Growth characteristics have a complex inheritance pattern, and the gene-environment interaction makes predicting tree responses to environmental change difficult. The primary goals of this study are to evaluate the variation in growth traits of different white poplar clones and to measure the inter-site variation and ecological sensitivities. In the experiment, a total of 30 white poplar clones were planted and measured over 5 years for height (H) and diameter at breast height (DBH) at four different sites in North China. ANOVA results showed that there were significant differences in H and DBH between clones at each site (P<0.01). Phenotypic and genotypic variation, and the repeatability of H and DBH, increased with the tree growth, which suggested that the inter-clone variation became gradually larger under the control of genetic factors. Under a selection ratio of 20%, the genetic gains of H and DBH also increased with the tree growth at the same site. Correlation analysis showed a significantly positive association between H and DBH both at the same age and sites, but the correlation coefficients decreased with increasing age. In conclusion, genetic gains were not equal between different sites, indicating differences in the influence of environment on the poplar genotype. Further investigations may be able to determine the role of environment for tree breeding programs and genetic selection.