Objective In order to further enrich the breeding resources of Populus deltoides, new germplasms with excellent comprehensive characters were created through intraspecific hybridization breeding of P. deltoides.
Method A total of 22 hybrid clones of P. deltoides were obtained by crossbreeding between P. deltoides ‘Ⅰ-69/55’ as the female parent and P. deltoides ‘D324’ as the male parent. The nursery stage and afforestation experiments were carried out with the female P. deltoides ‘Ⅰ-69/55’ as control. These clones were tested, and genetic variation analysis and principal component analysis were performed for seedling height and DBH, tree height and DBH from 1st to 8th year, 8th year stem shape, crown type and other characters, so as to comprehensively select excellent P. deltoides germplasms.
Result There were significant differences in seedling height and DBH, tree height and DBH from 1st year to 8th year, 8th year volume, crown width, branch degree, straightness and crown-height ratio among clones, but no significant differences in branch angle, subbranch height and branch thickness among clones. Moreover, the coefficient of genetic variation of each character ranged from 3.49% to 23.98%. In addition, the repeatability of seedling height, DBH, tree height, volume, crown width and branch degree were 0.6798−0.9405, which belonged to high repeatability and was under strong genetic control. Furthermore, there were different degrees of correlation between growth, stem, and crown traits of P. deltoides clones. The genetic correlation coefficients between DBH, tree height, volume, crown width and crown-height ratio in the 8th year were relatively high, showing a highly significant positive correlation. Additionally, principal component analysis showed that the cumulative contribution rate of the top three principal components was 86.85%, of which the contribution rate of the first principal component was 57.04%, and the DBH, tree height, volume, crown width and crown-height ratio contributed the most to the first principal component, which could be used as the evaluation index of clones. There were five clones, i.e. 616, 607, 609, 623, and 624, whose first principal component value exceeded the control P. deltoides ‘Ⅰ-69/55’.
Conclusion There are abundant genetic variations in the intraspecific hybrid clones of P. deltoides. The created five clones have excellent characteristics such as fast growth, straight trunk, large crown width and high crown-height ratio, and the comprehensive traits are better than those of control P. deltoides ‘Ⅰ-69/55’. So they are excellent germplasms.
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