Variation in growth, leaf, and wood property traits of Chinese white poplar (Populus tomentosa), a major industrial tree species in Northern China

The natural phenotypic variation in Chinese white poplar (Populus tomentosa Carr.), which is distributed across a wide geographical area of northern China (30 degrees N-40 degrees N, 105 degrees E-125 degrees E), is a potential source of beneficial variation for poplar breeding. Thirteen traits related to growth, leaf, and wood properties were quantified in 460 P. tomentosa individuals grown in a common garden plot. There was considerable range-wide phenotypic variation in all traits across individuals according to the patterns of ANOVA among hierarchical groups (populations and regions, respectively). A clear sexual dimorphism for seven traits was examined. In total, 32 trait-trait phenotypic correlations (P <= 0.05), 10 trait-geographical factor correlations (P <= 0.05), and a highly interrelated structure network were identified, which was further supported by principal component analysis (PCA). These associations can be used in multiple-trait selective breeding programs for advantageous phenotypic traits. A hierarchical cluster analysis was used to classify four groups (southeastern, central, northeastern, and southwestern populations) among the natural populations using these 13 phenotypic traits. This study provides important perspectives into the use of direct breeding to potentially improve economic traits and provides a starting point for genome-wide association studies in P. tomentosa in the near future.