Abstract: [Objective] To evaluate genetic gain and effect of improvement of the first-and the second-generation clonal seed orchards of Pinus massoniana, and to provide guidance for the breeding, production and application of the genetically improved P. massoniana.[Method] Two 6-year-old progeny trials of open-pollinated families of P. massoniana using materials respectively from the first-generation and the second-generation seed orchards in Zhejiang Chun'an and Fujian Shaowu were measured for evaluation of growth performance, analysis of genetic variation and gains, and estimation of breeding values of the families.[Result] There are large differences between progenies from different generations of seed orchard, while major growth traits including tree height, DBH, and volume all were higher than those of the control (i.e. the bulk selection from superior natural stands). The average individual volume and breeding value of the progenies from the first-generation seed orchard were 55.78%-84.62% and 40.66%-71.39% higher than those of the control, while these values were 58.96%-108.97% and 42.97%-91.89% for the progenies from the second-generation seed orchard. In general, progenies from the second-generation seed orchard exhibited greater growth rate and higher genetic stability than that of the first-generation seed orchard. There were significant differences in major growth traits among progeny families of the same generation. Tree height, DBH, and volume of the best family from the first-generation seed orchard were 21.94%, 30.72% and 97.75% higher than that of the poorest family. The traits of the best family from the second-generation seed orchard were 23.42%, 29.60% and 90.09% higher than that of the poorest family. These results indicated that re-selection of the parental lines from seed orchard will be essential. The tested families were classified into four types, i.e. "fastest-growing", "fast-growing and stable", "fast-growing and unstable", and "slow-growing", which accounted for 23.68%, 26.32%, 21.05% and 28.95%, of the total number of families respectively. The types of "fastest-growing" and "fast-growing and stable" could be used for establishing the new second-generation clonal seed orchard. Interactions of site×family and block×family were detected, indicating that the growth performance of families were diverse across different environment.[Conclusion] The effect of genetic improvement of progenies from the clonal seed orchard of P. massoniana was outstanding, and genetic gain of the second-generation seed orchard was larger than that of the first-generation seed orchard. Selecting the "fastest-growing" and "fast-growing and stable" parental lines is suggested in the selective-thinning of the old seed orchard and the establishment of the new seed orchard. The utilization of the singular-line parent with superior growth performance and high yield of seeds is suggested, mainly due to the interaction of environment×genotype and the diverse growth performance of families across different environments.

Key words: Pinus massoniana, generation, family, genetic variation, realized gain, breeding value