Abstract:

Genetic improvement for Loblolly Pine (Pinus taeda) in China has entered the second generation. Ellite individuals from the first generation progeny tests were selected and included in advanced seed orchard. Combined selection, I.e. selection of superior individuals with superior families, was adopted. In order to predict genetic gains of selection, correctly estimated heritabilities were essential. So far, several authors had published heritabilities for growth traits of Loblolly Pine in China. Most of them were estimated with biased data and plot means. Single-tree heritabilities were over-estimated in these cases. Up to date, there is no publication about within-family heritabilities for this species in China. In this paper, single-tree, within-family and family mean heritabilities for the growth traits of Loblolly Pine were estimated with the data from a two-site half-sib progeny test. The test was situated in Yingde (24°15′N, 113°45′E), Guangdong Province and Fuyang (30°15′N, 119°58′E), Zhejiang Province respectively. 24 common families from Yingde Loblolly Pine Seed Orchard were included. Randomized Complete Block design was adopted with 6 replicates, 6-tree row plot in Yingde and 8 replicates, 4-tree row plot in Fuyang. Variance components estimated by SAS^? /STAT VARCOMP Procedure with restricted maximum likelihood (REML) method were used to estimate the heritabilities. Three types of heritabilities were 0.161, 0.129 and 0.579 respectively for height, 0.075,0.059 and 0.384 respectively for diameter breast-high (DBH) and, 0.104,0.082 and 0.471 for single-tree volume at the age of 6 years. Meanwhile, genetic gains of combined selection were estimated using 3 equations according to Hodge and White (1992), and Falconer (1989). In spite of the severely imbalanced data, results from the 3 equations were extremely closed, showing that the handy equation, which is conducted with the family mean and within_family heritabilities and the corresponding selection differentials, is practical and reliable.

Key words: Loblolly Pine (Pinus taeda), half-sib progeny, combined selection, heritability, genetic gain