Comparison of tetraploid Betula platyphylla wood fiber traits and selection of superior seed trees

In this paper, we compared 31 tetraploid seed trees and three diploid Betula platyphylla seed trees in terms of their wood property traits and growth characteristics. The measured traits include DBH growth increment, stem straightness, wood density, fiber length, ratio of fiber length to width, content of lignin, cellulose, and holocellulose. The measured data were then analyzed in terms of variance with multiple comparisons. The results showed as the following: the differences in traits among the seed trees reached a significant level (P < 0.01). Of the 31 tetraploid seed trees, the fiber length of 24 was significantly higher than that of the diploid birch. In addition, the cellulose content of 13 seed trees was greater than 70%, and that of 12 was higher than 50%, which indicated that birch had significant effects on the traits of wood fiber after chromosome doubling, thus we can choose the good seed trees used for pulp material in tetraploid trees. Among the experimental seed trees, there were eight seed trees with a DBH amount of 2.00 cm or above, and all of them were tetraploid birch. According to the DBH growth and wood traits, using the subordinate function to comprehensively evaluate the experimental seed trees, the results showed that: the seven best performing birch seed trees were all tetraploid seed trees, which indicated that chromosome doubling can improve the growth of birch trees and the material properties of pulp and paper. Although the performance in terms of stem straightness was poor, with only 42% of the seed trees having straightnesses of grade Ⅱ orⅠ, but as pulpwood, the requirements of traits may be less strict. Finally, 19 seed trees were preliminary selected, of which the DBH growth and wood traits were all excellent, and five of them had optimal performance in terms of growth, wood properties and trunk shape. In the seed orchard, five tetraploid seed trees which have poor growth and wood properties will be eliminated.