Multipoint growth trait test of half-sibling offspring and excellent family selection of Betula platyphylla

Carrying out multipoint test for half-sibling families of seed orchard can not only select excellent families with superior growth traits but also accelerate the improvement progress. The height (H), diameter at breast height (DBH), volume (V) of 53 half-sibling families from birch primary seed orchard, which were planted in Langxiang, Maoershan, Jilin of northeastern China 12 years ago were used for multipoint conjoint analysis. The results showed that there were statistically significant (P < 0.01) differences in H and V among different families and sites, and also significant in site×family interaction.The differences of DBH among different sites and families also reached statistically significant level (P < 0.01). According to multiple comparison result, excellent families were preliminary selected in various sites. Meanwhile, breeding value of tested families was estimated adopting best linear unbiased prediction model "BLUP" and the tested families were synthetically evaluated based on the level of breeding value. Using a selection rate of 20% as the standard, B34, B15, B28, B16, B51, B40, B42, B45, B48, B35 and B19 were selected as superior families, whose mean volume was 8.29%, 9.80% and 13.60% higher than the mean value of Langxiang, Maoershan of Jilin, and the genetic gains of volume trait in the three sites were 3.23%, 7.16% and 8.84%, respectively. The mother trees of these families were selected as excellent tree, in which the mother trees of B34 and B15 were the best. These results provide a theoretical basis for selection and a reference for the improvement of seed orchard.