Genetic Diversity In Three Different Year Planted Offspring Stands From Masson Pine Clonal Seed Orchard

Genetic diversity of filial generation stands form masson pine (Pinus massoniana) clonal seed orchard planted in three consecutive years 1995, 1996, and 1997 was analyzed by microsatellite (SSR) marker. Based on the study of genetic diversity, the strategies to improve P. massoniana were also discussed. The results were as follows:1. Nine polymorphic primers (PR4.6,PTest1,PTest4,PtTX2146,Pr203,RPTest4,RPTest1, RPTest11,PtTX4062) were screened from 152 primers developed in P. taeda, P. radiate, P. sylvestris, P. cembra, et al. The number of alleles per locus was from 4 to 14, and the total polymorphic alleles in all loci was 72 which meant per locus had 8 alleles on average.2. According to the genetic diversity of filial generation stands, the ranking among them was the 1997 population > the 1996 population > the 1995 population. The result was caused by different physiological maturity, flowering circumstances. With flowering ages of ramets in the seed orchard increasing, there were more and more types of gametophores, therefore genetic diversity of the three consecutive years exhibited an increasing trend.3. Coefficient of genetic differentiation was 0.0105 on average and the majority of genetic variation occurred within population. Meanwhile coefficient of genetic differentiation among families was 0.0708 and the majority of genetic variation occurred within family. The mean of gene flow (Nm) was 3.2817, which showed relatively high level of gene flow among families. Predominantly outcrossing, wind pollination might be the main reasons of low genetic differentiation between families.4. At the population level, the average of observed heterozygosity (Ho) was 0.5208, much higher than expected heterozygosity (He=0.4786). The fixation index (F) was -0.1085 on the average and there were significant deviations from Hardy-Weinberg equilibrium in three populations. This case was concerned with material, there was selection press such as natural selection and artificial selection on filial generation, all eliminated individual might be homozygote, so heterozygosity of filial generation determined forests was enhanced.5. Two-locus analysis revealed the existence of significant linkage disequilibria per population and the different number of pairs showing significant linkage disequilibria per population. The findings, D_ST² > D_IS² and D'_IS² > D'_ST², implied that the stochastic cases such as genetic drift might be the main reason of linkage disequilibria.According to the facts that the majority of genetic variation occurred within populations and families, in the course of improvement of Pinus massoniana, emphasis should be put on selection of good families within population and good trees within families.