Characteristic variation and selection of forepart hybrid clones of Sect.Populus.

A total of 30 white poplar hybrid clones were used to study the phenotypic variation of growth and morphological traits in terms of stem height, diameter, trunk shape, leaf size, and stomata size. Results from the analysis of variance showed that remarkable differences existed in each of the 14 traits measured among these clones（P＜0.001), with the coefficients of phenotypic variation ranging from 15.63% to 57.50%, coefficients of genetic variation ranging from 8.99% to 52.57%, and repeatabilities ranging from 0.773 4 to 0.984 8 The analysis of phenotypic correlation showed that there were significant correlations among stem height, diameter, diameter at breast height, and volume per plant. Principal component (PC) analysis showed that the first three PCs explaining growth traits, trunk shape, and leaf traits, respectively, contributed accumulatively 84.93% to the phenotypic variation of the 14 traits. With a selection rate of 10%, BL206, BL207 and BL204 were selected as the best clones. Genetic gains through these three superior clones were 27.41% for height, 31.73% for diameter, 32.90% for diameter at breast height and 102.37% for stem volume. These results provide important information and basis for white poplar breeding in the next stage.