| Chinese pine (Pinus tabuliformis Carr.) is an important timber, ecological and landscape tree species in Northern China. Genentic improvement of this species has had a history of>40 years. To date, there are 16 improved variety bases of Chinese pine in China, most of which are at the first-cycle improvement stage and need to turn into the advanced-cycle stages. Key theoretical and technical issues related to advanced-cycle genetic improvement of Chinese pine were studied in this paper, which include genetic variation of important economic traits at the levels of provenance, family, individual and clone, determination of general combining ability (GCA) and special combining ability (SCA), evaluation and back selection of parents based on breeding value, selection and phylogenetic analysis of superior progeny individuals, structural design of advanced-cycle breeding population, marker-assisted deployment design of advanced-cycle seed orchard, advanced-cycle breeding strategy of seed orchard with varying improvement backgrounds, marker-assisted advanced-cycle improvement strategies without the need to do control-pollination. Improved variety bases of Chinese pine with different improvement backgrounds were used as the cases. Field experiments and genetic tests are the main methods for study, SSR molecular marker was also used for study at the same time. The aim of this study is to provide theoretical and technical guidances for sustainable improvement of Chinese pine. The main results are as follows:(1) There were significant variations for 10-provenance derived seedings in adaptive and 4a growth traits in Pingquan (Hebei Province). Seedlings originated from Fangshan (Shanxi Province) had the highest survival rate, seedlings from Yanqing (Beijing) had the highest growth, while the adaptation and growth of seedlings from Pingquan (CK) were moderate or under moderate. The growth and adaptive traits were positively correlated to varying degrees. Survival rate and growth of seedlings with different provenances had the trend of increasing with the increase in geographic latitude of the provenance origin. There were significant variations among provenances for 20a stem volume growth of families in Zhengning progeny test (Gansu Province). Families from Malan, Caijiachuan and Zhongwan had relatively higher volume growth. These results will provide important references for germplasm selection of Chinese pine in the studied regions.(2) Results from the 10×5 tester design genetic test for the remaining 36 full-sib families in tree height and diameter at breast height (DBH) at 22a showed that there were significant variations in growth traits among female parents, but the variations in growth traits were insignificant among male parents and families. The variations in growth traits of Chinese pine progeny came mainly from the differences in the GCA of female parents. It might be an important improvement way to back-select female parents of superior families.(3) Results from genetic analysis of the 17-batch plus-tree progeny test, composed of 221 families at 20a, in volume growth at Zhengning Imporved Variety Base (Gansu Province), the 2-batch open-pollinated families of the seed orchard clones in volume growth at 23a at Xixian Imporved Variety Base (Shanxi Province), and the 39 open-pollinated families of the seed orchard clones at 22a, in height growth at Lushi Imporved Variety Base (Henan Province) showed that there were significant variations in growth traits among families in the test sites. Family-heritability and individual-tree heritability for volume growth among different batches of progeny test at Zhengning had the ranges of 0.34～0.69 and 0.12～0.46, respectively. Family-heritability and individual-tree heritability for tree height in the progeny test of Chinese pine at Lushi were 0.33 and 0.13, respectively. BLUP method was used to predict the breeding value of the female parents at Zhengning test site, and 28 clones (the female parents of elite families), with the relative breeding value of>1.10, were back-selected as elite family parents.20 and 14 elite clones were back-selected according to the dominance ratios of growth traits between test families and test mean. The back-selected elite clones are superior germplasm for the second-cycle genetic improvement of Chinese pine in the corresponding bases.(4) Results also showed that there were significant variations among clones in growth and reproductive traits at Pingquan Imporved Variety Base (Hebei Province). The production of female and male strobili had the repeatabilities of 0.62 and 0.52, respectively. The growth and reproductive traits of clones were insignificantly correlated. Results from this part will provide references for fruiting ability-based clone selection.(5) 20 individuals, with the volume dominance ratios surpassed 11～60% of test mean, were selected as superior individuals in Xixian. The population constructed using superior individuals were stable (with mean fixation index (F) of -0.0184) and had high levels of genetic diversity (with mean polymorphic information content (PIC) of 0.5324) based on the 11 polymorphic SSR primers analysis. The phylogenetic relationship among individuals were also analysed based on SSR markers, which had provided the bases for deployment in advaned-cycle improvement of Chinese pine.(6) 40 superior individuals were selected in the no-peditree plantations constructed using open-pollinated seeds of the first-generation Chinese pine seed orchard. The dominance ratios of 20a vlomume of these individuals were 20～215%, which was significantly higher than that selected from the progeny test. These 40 individuals belonged to 23 families with varying genetic distances. The population constructed using superior individuals had high levels of genetic diversity (with mean PIC of 0.6202).(7) 20 and 23 Clones grafted using fresh scions of the superior individuals were used as parents for the second-cycle seed orchard in Xixian and Zhengning Imporved Variety Bases, respectively. Upon deployment, the relative magnitude of volume growth and SSR-based genetic distance (phylogenetic distance) were both considered in the second-cycle seed orchard in the corresponding bases. In Xixian, clones were grouped according to the relative dominance ratios of volume. The criteria of deployment in Xixian are that clones in high volume group were represented with higher proportion than in low volume group, and adjacent clones in the same block should have above moderate phylogenetic relationship. In Zhengning, clones were grouped according to the phylogenetic relationship.23 clones were first grouped into 5 phylogenetic groups (clones in the same group had close phylogenetic relationship, while clones in different group had distant phylogenetic relationship), and then grouped into 6 deployment groups (derived from clones in different phylogenetic groups, clones in the same deployment groups had distant phylogenetic relationship).6 deployment group formed into one complete, fixed block. Within a block, clones with high volume growth were represented with higher proportions than those with low volume growth. This study had proposed the unbalanced, grouped, fixed deployment design for clones in advanced-cycle seed orchard, which had solved the technical issues of high genetic value clones with more production, keeping rationable genetic diatance among adjacent clones, and decreasing the possibilities of inbreeding.In addition, the improvement strategies of the first-generation Chinese pine seed orchards with different improvement backgrounds were discussed in this paper, which would provide some experiential and technical references for advanced-cycle improvements of Chinese pine and relative conifers. |
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