Study On The Selection Strategy Of Populus Tomentosa Breeding Parents Based On SSR Markers

Populus tomentosa is a unique native species of China,and the maternal effect is not fully utilized in the genetic improvement.The solution of the relevant problem is of great significance to promote the research progress of the genetic improvement of Populus tomentosa.469 superior trees stored in germplasm bank,30 half-sib families and 34 full-sib families obtained in the early stage of the research were used as materials.In order to select hybrid parents with high specific combining ability for growth characters,we carried out the analysis on the genetic differentiation of the excellent clones of the poplar germplasm,the verification about the correlational relationship between specific combining ability and genetic distance of crossing parents,the identification of the male parent of superior half-sib Populus tomentosa individuals,the construction of hybrid parental combinations with high specific combining ability,the evaluation of the full-sib progenies,and the analysis of genetic composition and transmitted parental heterozygosity of natural 2n gametes in Populus tomentosa based on SSR molecular marker technology.The main resu ts are as follows:(1)Polymorphic SSR primers library and superior clones fingerprint database were constructed in Populus tomentosa.The DNA template of 469 clones was used to screen out the 406 pairs of SSR primers with clear,specific,polymorphic,stable amplification profiles.The distribution of the selected primers was between 3 and 39 pairs on 19 chromosomes of Populus trichocarpa.,389 pairs of SSR primers were located in the Populus trichocarpa genome by BLAST analysis,and the polymorphic SSR primers library was constructed.At the same time,25 pairs of polymorphism SSR primers and 13 specific SSR auxiliary primers were selected through the identification efficiency analysis of SSR primers,and the fingerprints of 469 superior clones were constructed.Moreover,the QR codes of these fingerprint were completed.The research has laid a foundation for future genetic resources management,variety identification,parental analysis and intellectual property protection.(2)Parental identification of the superior offspring and the reconstruction of hybridized combination with high special combining ability can be efficiently carried out by using SSR molecular markers.Based on the comprehensive evaluation of the eight main growth traits of 2292 plants from 30 half-sib families,77 individuals consisting of 43 triploid and 34 diploid progenies were selected as superior plants.We applied 14 pairs of high polymorphic SSR primers to identify the male parents of the 77 superior plants.Our results indicated that 29 male trees as the pollen parents of 59 superior plants from 49 cross combinations including 17 female parents and 29 male parents.(3)The breeding parent population was preliminarily constructed according to SSR genetic distance.The correlation analysis was conducted between specific combining ability for the growth characters of 34 hybrid combinations and SSR genetic distance among parents,and a significant positive relationship was found.The SSR genetic distance can be used to predict the hybrid parental combination with high special combining ability.Furthermore,SSR genetic distance between 18 female and 68 male selected in the early stage was estimated,and the potential 1224 hybrid parental combinations were compressed to 52 crossing with high special combining ability,the breeding parent group was screened,including 15 female parents and 12 male parents.We construct the breeding parental group including 14 potential hybrid combinations by SSR genetic distance and superior individual paternity test,and there are 10 maternal and 5 paternal parents in breeding parental group.(4)Parental identification and parent genetic distance prediction can rapidly construct the hybrid parental combination with high combining ability by SSR molecular markers.Refer to the predict results by parental identification and parental genetic distance analysis,We choose three maternal and six paternal parents in breeding parental group to constructe five target hybrid combinations and three control cross combinations,and a total of 3984 offsprings were obtained.Differential source analysis of plant height and ground diameters of different hybrid combinations indicated that the influence of maternal and paternal interaction on the height and ground diameter of offspring is remarkable.The height and ground diameters of the 5 target hybrids were significantly higher than the control cross combinations from the same female parent.There was a large variation in plant height and ground diameter in each hybrid combination.The variation coefficient of height and ground diameter of the control was larger than that of target hybrid combinations.Preliminary findings indicate that the hybrid combinations predicted by parental identification and parental genetic distance can obtain offspring with superior growth performance.(5)The existence of natural 2n female gametes was found for the first time,and the study proved that genetic constitution and transmission of heterozygosity characteristics of natural 2n male and female gametes.the source of 87 natural triploid obtained from the hybridized combination "T-F-14×T-M-43"was identified based on SSR markers.18 natural triploids,which is 20.68%of the total number of triploids in this hybrid group,origined from 2n female gametes.Four SSR loci with low homologous recombination rate were used to identify the genetic constitution of 2n male and female gametes,which proved that there are 6 triploids originated from the FDR 2n female gamete and 12 triploids originated from the SDR 2n female gamete.In addition,there are 55 triloids originated from FDR 2n male gamete and 14 triloids originated from SDR 2n male gamete.Meanwhile,transmission of parental heterozygosis by 2n gametes was analyzed based on 42 pairs of SSR primers,which indicated the heterozygosity of 2n female gametes was lower than that of 2n male gametes.(6)A more reliable selection strategy for selection of breeding parent with high combining ability is presented.In the superior clone breeding of Populus tomentosa and similar tree species,the high fertility parents were screened by pollen and seed observation in the germplasm bank;The genetic distance between parents with high fertility was analyzed using SSR markers.Furthermore,the potential high specific combining ability breeding parents were screened based on certain genetic distance criteria,and constructing the primary breeding parents group.Meanwhile,the female parents from the primary breeding parents were used to construct the half-sib families.We screened the superior half-sib individuals,and carry out the parental identification of superior half-sib individuals based on SSR markers,which realized the selection of parents with high combining ability and the construction of breeding parent group quickly and efficiently.