| Alnus cremastogyne Burk.is an important native tree species distributed in Sichuan,Chongqing and other places in Southwest of China.It inhabits in area with high sunshine and high wet,and with good tolerance to drought and barren,occupying important position in construction of local forestry economy and ecological civilization.It is significant for parental selection in genetic improvement strategy of A.cremastogyne to analyze genetic variation in population and relationship between parental genetic distance and combining ability.In this study,population genetic diversity,genetic distance of plus trees and selection breeding parental of A.cremastogyne were studied in phenotypic trait markers and SSR molecular markers based on plus tree population from 14 provenances.The main results are as follows:(1)Significant morphological variations in tree trunk,leaf and flower were found among different natural populations and individuals in population in A.cremastogyne.Straightness of trunk had big difference among populations,and the change trend of the trunk straightness was significant varied within population.Coefficient of variation of leaf morphological traits were 14%-32%,with Shannon diversity index more than 1.50.The PCA analysis of leaf traits distinguished Mianning,Luding and Yanting groups from other groups;PCA analysis of fruit traits distinguished Mouchuan,Pingwu,Meigu and Mianning groups from other groups.The average air-dry density of the Alnus population was 0.4878g/cm3 with 9.52%coefficient of variation.Yanting,Xuanhan and Jiange groups had the highest average air-dry density.Genetic diversity indices of morphological traits were correlated with geographical factors.Significant negative correlations were found between leaf length,leaf width,leaf area,or fruit length and elevation,and there was a significant positive correlation between fruit width and elevation.The There was a moderate negative correlation between air-dry density and altitude.(2)After transcriptome sequencing of the apical buds,male flowers,female flowers,leaves and cambium tissue of A.cremastogyne,and de novo assembly with Trinity,184,689 unigenes were found.5.08%?27.21%of them matched to the NR,uniprot-swissprot,GO,KOG,KEGG and other databases.A total of 61,568 SSR loci were searched and distributed on 44,828 unigenes with a frequency of 24.27%.Most of the SSR loci(28961)were mono-nucleotide repeat SSRs,accounting for 47.04%of the total SSRs,and di-nucleotide repeat SSRs were counted 13,617(22.12%).30 loci were randomly selected to design primers,and 8 pair polymorphic primers were screened for genetic diversity analysis.Most of unigenes had no annotation information.The GO,NR,Swiss-Prot,KEGG,and KOG databases respectively annotate 16.81%,13.88%,11.73%,5.08%,and 27.21%of unigenes,differentially expressed genes indicated the expression patterns of genes from early flower development were similar to the young leaves,the number of differentially expressed genes between male and female flowers was the highest.(3)Based on our protocol for SSR analysis of polyploids in Alnus,25 microsatellite primer pairs with high polymorphic information were screened to analyze genetic diversity of Alnus populations.The results showed that the mean number of observed alleles,effective alleles,observed heterozygosity,and expected heterozygosity were 5.83,3.37,0.739 and 0.63,respectively,indicating that Alnus exhibited an above average level of genetic diversity and the genetic diversity of populations were different.The Liangshan populations(including Meigu and Mianning)possessed the higher genetic diversity than others.The genetic differentiation coefficient(Fst)in 14 populations was 0.021,in accord with results of analysis of molecular variance(AMOVA),indicating that genetic variation within populations was higher than that among populations.Meanwhile,the gene flow among populations averaged at 11.114,suggesting that the gene introgression among populations was frequency which weakened genetic differentiation among populations.Both the UPGMA clustering and the population structure analysis suggested that 14 populations of Alnus might be originated from three original genetic populations,which presented geographical distribution feature especially in elevation.(4)Through 7 × 7 full double-column hybridization,the results showed that highly significant differences were found in nut,nut traits,seedling height and ground diameter among different crosses.Four good combinations Jintang 4 × Qionglai 13,Bazhong6×Jiange6,Baizhong6 × Emei2 and Bazhong 6 X Qianjiangl were selected.Nursery test showed that the specific combining ability of ground diameter was significantly correlated with SSR genetic distance,suggesting that the parental combination could be selected according to the genetic distance of the mother tree to produce better hybrid progeny.The breeding parent population consisting of 31 plus tree with potential high-altitude special combining ability was constructed based on the genetic distance average and 2.5 standard deviations. |
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