Differences in Fiber Properties and Basic Wood Density in Triploid Hybrids of Populus Tomentosa

In forest breeding programs, growth has typically been used as a selection trait of prime importance in Populus tomentosa, whereas less attention has been given to fiber characteristics and basic wood density. Given this context, we investigated phenotypic relationships between different fiber properties, growth and basic wood density traits in nine triploid clones and one diploid clone based on a clonal trial established in 2004 in northern China. We found that fiber width showed, on average (1.4%), the lowest phenotypic variation followed by fiber length (2.2%), coarseness (5.3%). Basic wood density showed, on average (1.9%) phenotypic variation. All phenotypic correlations between fiber properties were positive ( p＜0.05), ranging from moderate to strong, suggesting that selection for one trait could simultaneously affect other traits. Phenotypic correlations, on average, were quite weak but positive between growth and fiber properties and slightly negative between basic wood density and different fiber properties ( p＜0.05). Individually, some of the triploid clones showed negative correlation between growth traits and fiber length. As a result, selection for fiber properties alone could reduce overall stem volume and would not directly indicate basic wood density traits and vice versa.