Study On The Hybridization Effect Of Ginkgo Biloba L. Based On Whole Genome Selection

Ginkgo biloba L.,commonly known as ginkgo or maidenhair tree,is a dioecious plant with a history of hundreds of millions of years.Hybridization is one of the main forms of natural generation replacement for ginkgo.Peter Cane,a renowned botanist from Yale University,discovered through an exploration of ginkgo’s history that the overall morphology of ginkgo has remained largely unchanged for over 200 million years.Based on this,this study utilized GBS sequencing to investigate the genomic variations of the main conserved germplasm resources of ginkgo.The study analyzed the genetic diversity,genetic structure,and phylogenetic relationships of ginkgo,and performed a genome-wide association analysis combining the important phenotypic traits accumulated over a long period of ginkgo seed development.Subsequently,based on the genetic background and phylogenetic relationships of the conserved resources,an artificial hybridization system was constructed to collect hybrid seeds and cultivate the F₁ population.The study further analyzed the phenotypic differences of the ginkgo hybrid seeds,as well as the growth,development,physiological and biochemical effects at the F₁ seedling stage,and performed a genome-wide association analysis of the F₁ offspring,early gender identification,and analysis of sexual dimorphism within the F₁population.The main research conclusions are as follows:（1）The 102 accessions ginkgo cultivars could be divided into four subpopulations from G1 to G4,with genetic differentiation indices between 0.164 and 0.432 and nucleotide diversity indices between 7.843e^-04 and 1.72e^-03 among the subpopulations.Most of the germplasm showed no obvious affinities among them except for a few cultivars.A total of 54 SNPs were identified and associated with seed nucleus traits,and 24 candidate genes such as Gb＿39567,Gb＿07833,and Gb＿19888 were annotated,which were combined with ginkgo seed nucleus traits and GBS genome-wide SNPs information for association analysis.It provided genetic resources for further precise localization and gene validation.（2）We constructed a 3×3 ginkgo artificial hybrid system based on genetic distance and relatedness among the major germplasm.The shape coefficient,fresh weight,and ash content of the hybrid seeds were significantly affected by the parent only after variance analysis of the harvested seeds.The total starch content in the seeds was not significantly associated with the parents.The smaller the seed type coefficient,the higher the glutinousness of the seeds.There was no significant difference in the ratio of MPN and MPNG contents in the seeds of the crosses.The seed traits were mainly influenced by maternal genetics,and the degree of intra-strain variation was less than inter-strain variation.（3）The seedling height,ground diameter,and shoot growth of ginkgo hybrid F₁ population had rich intra-population variation,and the coefficients of variation were 25.02%,24.83%,and34.25%,respectively,which showed no obvious differences in parental genetic tendency.There was no significant difference in net photosynthetic rates between control and free pollination hybrid offspring.The inheritance of total chlorophyll and chlorophyll a content in hybrid offspring may be greatly influenced by maternal origin,and the inheritance of chlorophyll b content between relatives and offspring is more paternal.The genetic contribution of the hybrid parent to the soluble sugar content of offspring leaves was greater,with an average genetic transmission force of135.59%.The mean coefficient of variation of the soluble protein content within the hybrid progeny population was 21.82%,and the mean genetic transmission power was 109.98%.The average coefficient of genetic variation of total flavonoids content was 23.16%,and its heritability had a stronger maternal effect.The average genetic coefficient of variation of ginkgo terpene lactone content in the offspring population was 28.81%,also with a stronger hybrid maternal effect.There is a clear positive correlation between the growth and development index（seedling height,ground diameter,new shoot growth amount）,total chlorophyll content and net photosynthetic rate.No significant correlation was shown between the main inclusions of ginkgo leaves.（4）The effective allele（Ne）of the ginkgo hybrid F₁ population was slightly higher than that of the ginkgo cultivar population,indicating that the variation of the ginkgo hybrid offspring population was not weaker than that of the ginkgo cultivar population before crossing.The genetic distance of each offspring population was smaller than the mean genetic distance between the parents in the crosses.The farther the distance between the maternal parent in the ginkgo hybrid,the higher the genetic differentiation of the offspring.Most of the variation in ginkgo hybrid offspring came from within populations（91.46%）,and the genetic variation between populations accounted for only 8.54%.The 27 SNPs and 12 candidate genes associated with total chlorophyll content,176 SNPs and 80 candidate genes associated with soluble sugar content,44 SNPs and 23candidate genes associated with total flavonoid content,and 34 SNPs and 14 candidate genes associated with terpene lactone content were localized in combination with each index and genome-wide SNPs loci of ginkgo F₁ single plant.（5）The male to female segregation ratio of the hybrid offspring was 0.79 based on the results of PCR amplification of the offspring.The nutritional growth capacity of male plants was significantly higher than that of female plants at the seedling stage of the ginkgo hybrid offspring.The net photosynthetic rate of male offspring at seedling stage was higher than that of female offspring,while the remaining photosynthetic indexes were not significantly different.The total chlorophyll,chlorophyll a and chlorophyll b contents of male plants were significantly higher than those of female plants,while carotenoid contents were not significantly different.The soluble sugar and soluble protein contents of the male plants were significantly higher than those of the female plants,123.57%and 121.15%of the female plants,respectively.The total flavonoid content of female plants was significantly higher than that of male plants,and the terpene lactone content was higher than that of male plants,but did not reach a significant difference level.A total of 48 specific genes were annotated in the female population,which were enriched in pathways such as caffeine metabolism,and 64 specific genes were annotated in the male population,which were mainly enriched in pathways such as thiamin metabolism.