| The flow cytometry was used to determine the ploidy of 469 clones of Populus tomentosa in a gene pool located at Guan County of Shandong Province.19 SSR markers were used to estimate the genetic diversity of all the diploid P. tomentosa clones. Among diploid clones, the seeds were collected from all female parents to evaluate the fertility ability and combining ability. According to pollen production measured by our group in early stage, the parental population for breeding was constructed by a comprehensive score for volume of timber, form quality, fertility ability and general combining ability (GCA). The main conclusions in this study as follows:(1)Higher percentage of natural triploid clones is observed among plus trees of P. tomentosa. The result of the flow cytometry showed that 28 natural triploid clones (including 24 female and 4 male clones) were detected, accounting for 6.0% of the total clones in the gene pool. Among those putative triploid clones, which were derived from Beijing, Hebei, Henan, Shanxi and Shaanxi, respectively.(2)The differences in fertility ability among all the female diploid clones were observed, and the clones with better fertility ability can be selected. The analysis of the fertility ability of diploid female clones showed that the seed-bearing coefficient ranged from 0 to 32.43. According to the data of the seed-bearing coefficient,10 female clones with higher seed-bearing coefficient, such as clone 3-97-2, 3-97-3,3353,3-10-2,3532,3119 and so on, were selected out, and 48 male clones with higher pollen production (including clone 3801,4421,9007,0095,1218) were selected.(3)Significant differences in stem volume, diameter at breast height (DBH), diameter of crown and branch angle were observed among these plus trees of P. tomentosa. Compared with the diploid clones, the triploid clones had some advantages on the growth trait. The biggest variation coefficient was seen in stem volume, suggesting that stem volume should be considered as a main standard in the construction of parental population for breeding.(4)Abundant genetic variation was observed among plus trees of P. tomentosa, and modest genetic diversity was detected.103 alleles locus were revealed by 19 SSR markers in diploid clones. The mean of alleles per locus was 5.4,1.95 effective alleles per locus were identified. The range of Nei’s genetic diversity index (He) and Shannon polymorphism information index (Ⅰ) were from 0.091 to 0.689 and from 0.191 to 1.575, respectively.(5)There are significant differences in the growth traits among the offsprings of all the half-sib families of diploid P. tomentosa. The seedling height and basal diameter of 30 half-sib families of diploid P. tomentosa were measured and the general combining ability (GCA) was estimated. The general combining ability of seedling height ranged from -12.3 to 13.7cm and general combining ability of basal diameter ranged from -0.17 to 0.17cm. The clone 3-10-2,2-8,3119,3206 and 3-10-1 had the best performance on the general combining ability (GCA) for seedling height and basal diameter.(6)The parental population for breeding in P. tomentosa was constructed by the comprehensive score. The parental population for breeding (including the female clone 3-10-1,2-8,3119,3-85-1, 3129,3-74-1,3-24-26,3-97-3 and male clone 4421,1258,4201,4128,4428,1306,4234,4338,9007, 5412,1271,4202,5026,1402) was constructed by a comprehensive score for stem volume, form quality and fertility ability. For the female parental population for breeding, the retention of observed alleles, effective observed alleles, Nei’s genetic diversity index (He) and Shannon polymorphism information index (Ⅰ) were 62.90%,75.83%,75.05% and 69.85%, respectively. For the male parental population for breeding, the retention of observed alleles, effective observed alleles, Nei’s genetic diversity index (He) and Shannon polymorphism information index (Ⅰ) were 58.59%,100.59% and 92.44%, respectively. |
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