Abstract: [Objective] This study was based on 8 older-than-15-years progeny tests of the first generation breeding population of Masson pine(Pinus massoniana) in Guangxi. On the basis of comprehensive evaluation of breeding objectives and genetic diversity, a second generation breeding populations of Masson pine was established. [Method] Progeny growth data was analyzed using the SAS software which was based on linear model, and according to the results, second generation plus trees were selected. SSR markers were used to analyze genetic diversity of the second generation plus trees, parental analysis and genetic distance estimation. According to the genetic distance among the 2^nd-generation plus trees, the second generation breeding populations was structured.[Result] In the progeny tests, the two families were significantly different in growth tratits. Most progenies have a family heritability above the medium level (h²≥0.2) in volume which was suitable for the selection of superior families. Based on this, selection of second generation of breeding population can use the combined individual selection and mass selection. 163 trees were selected from the progeny tests, and the average genetic gain was 21.95%. The genetic diversity of the second generation breeding materials was studied by using 16 pairs of SSR primers. A total of 45 alleles were detected at 16 loci. The mean number of alleles (N_a) per locus was 2.7, polymorphism rate was 100%; the mean number of effective alleles (N_e) per locus was 1.54; Shannon diversity index (I) was 0.49 and the average observed heterozygosity (H_o) was 0.32. Using the Coancestry Version 1.0 software to calculate the average second-generation breeding population, the coancestry coefficient was 0.042 and the breeding population status number was 11.9. According to the 16 pairs of SSR primers amplified, second generation breeding population of male parents were analyzed by the CERVUS2.0 software, and the results indicated that the second generation of the 163 tress, male parent could be determined for 57 individuals under the 95% confidence level, and for other 102 individuals under the 80% confidence level. In order to avoid inbreeding in advanced generations, the second generation breeding populations were clustered with the genetic distance index. According to the results of distance clustering, the 163 individuals were divided into 10 sub-lines, numbered from Gui GC2-A-Gui GC2-J. In the establishment of the second generation seed orchard of Masson pine, following strategies was proposed for 2^nd-generation seed orchard: a certain number of best clones from each sub-line were chosen to establish 2^nd generation seed orchard; mating among the sub-lines was adopted in cross breeding of the next generation, so that the overall level of inbreeding in the breeding population can be maintained at a relatively low level. [Conclusion] According to preliminary results, the second generation breeding population of Masson pine in Guangxi was composed of 163 trees. This population had a high genetic diversity, and a low degree of inbreeding among individuals. The second generation breeding population was clustered by the genetic distance, and the strategies of advanced-generation cross breeding were designed: large scale hybridization was carried out among the sub-lines, but only the small scale hybridization experiment was carried out in the sub-lines. The strategy can be applied to effectively avoid inbreeding, laying a foundation for advanced-generation cross breeding of Masson pine.

Key words: Pinus massoniana, breeding population, SSR, genetic diversity, parentage analysis