| Masson pine (P. massoniana) is one of the conifers native tree species in south china with better quality of fast growth, wide distribution and strong resistance, and used widely in papermaking, building and rosin. In this thesis, 12 years old (1/2 rotation) of P. massoniana with nested mating design was studied to reveal the mode of genetic control in growth and wood quality, some superior crossing combinations and superior individuals were screened for adding to second-generation breeding population of masson pine. The genetic variation of major growth and reproductive traits and the correlation with the genetic background of breeding parents were researched by breeding population and third-generation germplasm formulated by second-generation breeding parents, and the mode of genetic control in seedling growth were also investigated, which would provide theoretical basis and guidance for the selection of seed orchard parents and the formulation of excellent new germplasm based on the matching for second-generation parents. In addition, the genetic variation law of major growth, branching and reproductive traits was investigated in a dwarfed second generation clonal seed orchard of masson pine which had entered into normal flowering and seed setting stage, and the genetic mating system, genetic diversity and the correlation with flowering and fruiting traits were also analysised to provide important theories for genetic management in higher quality and yield of the second generation seed orchard of masson pine .The results are as follows:1. Male and female parents effects, additive effect and dominant effect of growth traits and wood basic density were investigated in a progeny test forestry of 12 years old of P. massoniana with nested mating design.The results showed that, except for stem straightness, there existed significant differences in growth rate and wood quality among the crossing combinations, male and female/male parents. Male and female parents effects worked on DBH, height, individual volume and stem fullness simultaneously, but the difference of effects was very little. For wood basic density, female parent effect was 1.56 times larger than male parents. DBH and wood basic density of P. massoniana were controlled by additive effect primarily, and then dominant effect, but height, individual volume and stem fullness were almost controlled by additive effect completely, progeny could be predicted by the performance of parents.The result of comparative analysis for growth and wood quality of crossing combinations and male parents clones showed that the correlation between growth and wood basic density was very little, for fast-growing male parents and crossing combinations, the wood basic density was not always low. The correlation between growth performance of crossing combinations and GCA of male parents was not obvious, but the probability to get superior crossing combinations would be raised through selecting male parent with high GCA to hybridizing. Ten superior crossing combinations and 17 and 13 superior individuals for pulp wood and saw timber were screened based on wood dry matter and DBH respectively.2. The average height, DBH and volume of tested 51 clones in the second generation breeding population were 5.53 m, 9.05 cm and 0.021 m3, respectively, the overall growth performance of masson pine was superior, and significant deviation in growth traits was detected between clones, phenotype genetic variation was abundant in the second generation breeding population. For reproductive traits such as cones number, the degree of variation was higher than growth traits such as height and DBH. Base on major growth traits and reproductive traits, the 39 tested clones were clustered into 4 groups, which exhibited large degree of variation in traits. Group 1 exhibited superior growth traits and large amount of female cones and young cones, whereas group 2 exhibited poor growth traits and cones amounts. In group 3, the growth traits and male cone amount was superior, but the female cone amount was poor. Group 4 exhibited poor growth traits but large amount of female cones and young cones. There was a weak negative correlation between growth traits and female cone amounts. From 39 tested clones, 28 superior clones were selected, which could be used for controlled pollination and seed orchard parents when combined the result of combining ability.3. 36 parental clones from the second generation breeding population of masson pine were assessed to detect their genetic variation at molecular level using 15 selected ISSR (inter-simple sequence repeat) markers, the Nei's genetic diversity was 0.328, the Shannon's information diversity index was 0.476, and the genetic distances ranged from 0.24～0.82 with an average genetic distance of 0.414, indicated that the genetic variation of the second generation breeding population was at high level, and had the potency for advanced-generation genetic improvement. The UPGMA clustering analysis based on genetic distance were done, the 36 clones was clustered into 5 groups, and the clustering was partially consistent with the background and genealogy of the clones. It was helpful for improving the growth performance and heterosis level of progenies to select cross parents from different groups and some genetic distance range (0.264～0.529) which had greater molecular genetic distance on the basis of the combining ability and background.4. Combining ability of seedling growth and shoot elongation parameters for the third generation germplasm of P. massoniana were investigated in a 6×6 half diallel cross design, which the parents were selected from the second generation breeding population. The result showed that, except for linear growth day(LGD), there existed significant differences in general combining ability (GCA) and specific combining ability (SCA) of seedling height, ground diameter, maximum growth rate (MGR), linear growth rate (LGR) and total linear growth (TLG), and the dominant gene effect was predominant over the additive gene effect for seedling height, MGR, LGR and LGD, especially for ground diameter, which was almost controlled by dominant gene effect completely, but for TLG, the additive gene effect was somewhat larger than dominant gene effect. The reason for this seemed to be that the indirect selection on GCA of growth had been made for mating parents.Compared to the second generation germplasm, which the mating parents had been indirect selected on GCA of growth, the change was little of genetic control model for this traits in the third generation germplasm, only the variance component of SCA had increased significantly. During the genetic improvement of the advanced generation in P. massoniana, the selection of SCA between parents should be strengthened, which would help to produce superior cross combinations.5. The genetic variation law of flowering and fruiting was investigated in the dwarfed second generation clonal seed orchard of P. massoniana which had entered into normal flowering and seed setting stage. The results showed that there existed significant differences in strobilus and cone production among the different clones, but there were not among clonal ramets, the genetic variation coefficient varied from 37.85% to 53.50%, and the clone repeatability was over 0.71. The clones could be clustered into four types, partial female type, partial male type, neutral type and few type according to the law of flowering and fruiting, which accounted for 25.00%, 29.55%, 38.64% and 6.82% respectively. About 20% high yield clones provided strobilus and cone for the whole seed orchard production from 41.27% to 49.15%. The results of correlation analysis showed that the optimum mother tree form traits of the dwarfed second generation seed orchard clones with high yield were as follows: larger crown, longer branch, flatter branch angle and wide egg-shaped crown or spheroidal crown etc.. Except for thousand-seed weight, there were significant differences between shaded halves and exposed halves of tree crown in the traits of cone and seed yield, and exposed halves was superior to shaded halves in the traits, which showed that ample illumination would help to improve the yield of seed orchard.6. The patterns of effective pollen dispersal were explored in an experimental population of the second generation clonal seed orchard of P. massoniana. The average observed and expected heterozygosity (Ho and He) are 0.402 and 0.446 respectively in experimental population. The average polymorphic information content (PIC) is 0.399. Every mother tree with 22 male parents produced progenies. The self-crossing rate reached 1.56% in open-pollination condition, and outcrossing was primary mating mode of the second generation clonal seed orchard of P. massoniana. The reproduction contribution was changed from 1% to 3% for the most of male parents, with average of 2.00% (produced 6.4 progenies). The most pollination events were detected in the seed orchard of P. massoniana ranged from 0 to 90 m, the maximum dispersal distance reached 185 m, and accord with normal distribution. The pollen contamination was only 4.06%. For the mating distance among parents, there was an increasing tend in the south progenies of crown compared with the north, but no obvious trend arised in the male parent numbers of the south and north progenies of crown.7. The level of genetic diversity in progeny population was the same as in maternal population in the second generation clonal seed orchard of P. massoniana, all alleles detected in progeny population were included in maternal population, there were not obvious surplus phenomenon of homozygotes in progeny population (F=0.047). The genetic diversity was not decreasing tend with reducing of strobilus in the north crown compared with the south crown. The progeny of neutral tree had the same level of genetic diversity as in the progeny of partial female tree, which the fixation index tended to be zero and accorded with Hardy-Weinberg equilibrium. The outcrossing rate of the seed orchard was very high, with 1.097, and biparental inbreeding was not significant (tm-ts=-0.031). The multilocus outcrossing rate and singlelocus outcrossing rate in the south crown were higher than the north crown. The multilocus outcrossing rate in progeny of partial female tree was the same as in progeny of neutral tree, and the outcrossing rate was not obvious decreasing tend with proportional reducing of female and male strobilus in neutral tree compared with partial female tree, which the fixation index tended to be zero. The level of genetic diversity and outcrossing rate in the second clonal seed orchard did not decrease with the increasing of artificial selection strength, gene exchange among clones was sufficient relatively, and biparental inbreeding was not significant.
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