Abstract: [Objective] The correlations between heterosis in growth traits of progeny and combining ability, genetic distance of their parents for Pinus massoniana were analyzed to select parents scientifically for hybrid breeding based on performance of the progeny. The study on heterosis, combining ability and genetic distance would provide guidance for the breeding of Pinus massoniana.[Method] Two sets of test materials from the third generation of P. massoniana grown in Laoshan Forest Farm of Zhejiang Province were used to investigate the heterosis and combining ability of growth traits in 6×6 half diallel cross designs. SSR markers were used to analyze the genetic distances between mating parents and the relationships between heterosis of the progeny and general combining ability (GCA), specific combining ability (SCA), genetic distance(GD) of the mating parents.[Result] Results showed that the phenotypic value and heterosis of growth traits exhibited significant differences between the two hybrid combinations. Except the GCA of DBH in the design II, the combining abilities of other growth traits were significantly different between different mating combinations. All growth traits but DBH in the design II were controlled mainly by the additive gene effects. For all growth traits, family heritability (h_f²) were relatively high (0.884-0.966), indicating a high level of genetic control for the growth traits. Genetic diversity of the 12 breeding parents was at a moderate level with Nei's gene diversity index of 0.301 2 and Shannon's information diversity index of 0.467 8. The GDs among parents were 0.142 1-0.351 6. Meanwhile, most correlations between phenotypic value, heterosis of growth traits and the sum of general combining ability (GCA_P1+P2), SCA, GD (≤ 0.351 6) were significantly positive. Among the GCAs of mating parents, GCA_P1+P2 was proved to have the strongest predictive ability for the phenotypic value and heterosis of growth traits, the general combining ability of male parents (GCA_P2) was the second, and the general combining ability of female parents (GCA_P1) was the weakest. Among the GCA_P1+P2, SCA and GD of the parents, GCA_P1+P2 was proved to have the strongest ability to predict the phenotypic value of growth traits, SCA was proved to have the strongest ability to predict the heterosis, and the predictive ability of GD for phenotypic value and heterosis was weaker than GCA_P1+P2 and SCA. Except the GCA_P1+P2 of cross design Ⅱ, other GCA_P1+P2, SCA, GD were found to have a significant linear correlation with the heterosis in volume index of the progeny.[Conclusion] Since there existed a relative closer correlation between GCA_P1+P2, SCA, GD (≤ 0.351 6) and phenotypic value, heterosis of growth traits, it is feasible to predict the phenotypic value and heterosis in growth traits by combining ability and smaller genetic distance to improve the efficiency of parental apolegamy and the utilization of heterosis for P. massoniana.

Key words: Pinus massoniana, germplasm, heterosis, GCA, SCA, genetic distance