Abstract: Progeny of 68 full-sib combinations from the first generation nucleus breeding population of loblolly pine (Pinus taeda) in Guangdong Province composed the base population of the second generation nucleus population. The height, diameter at breast height (DBH) and single-tree volume of the second generation nucleus population were measured in 8, 10 and 15 years. The result showed that there were extremely significant differences in height, diameter at breast height (DBH) and single-tree volume among the combinations. According to the growth performance of 15-year-old progeny, eight superior female parents and four male parents were selected. They could be used for establishing a elite seed orchard or a controlled pollination seed orchard to produce genetically-improved seed. The family-mean volume at the age of 15 year was used for the combination selection indicator and 10 combinations were selected, with the average gain of 18.94%. Seeds from re-pollination of these 10 combinations could be used to construct cutting nursery, and then cuttings from these superior full-sib families could be used for afforestation. By using combined selection, 55 individuals were selected to construct the second generation breeding population. Thirty individuals among them were selected into the second generation nucleus breeding population, remaining 25 into the second generation main breeding population.

Key words: Pinus taeda, nucleus breeding population, positive assortative mating, growth variation, selection