High-density Genetic Map Construction And QTL Mapping Of Agronomic Traits Of Ziziphus Jujuba Mill.

Jujube?Ziziphus jujuba Mill.?is a characteristic traditional economic fruit in China.In order to preferably break the theory and technology of jujube hybrid breeding.This study aims at quality,F₁hybrid population of Z.jujuba‘Dongzao'?high-quality fresh variety?×Z.jujuba‘Jinsi4'?edible both fresh and dried variety?was constructed with SSR molecular markers.The high-density SNP genetic linkage map of jujube was constructed by the GBS?genetic by sequencing?refer to two whole genome sequencing data of‘Dongzao'and‘Junzao'.Seventeen traits of leaf,needling and fruit were measured and analysised statistically,of which QTLs were identified by composite interval mapping?CIM?,meanwhile,screen the superior plants by principal component analysis to fruit traits.The main results were as follows:The 201-seedling natural crossing population was constructed with Z.jujuba‘Dongzao'and Z.jujuba‘Jinsi 4'.The progeny seedlings were genotyped and their male parents were identified using 8 pairs of polymorphic SSR primers.After genotyping by Cervus3.0,84alleles were detected in the population,with an average allele number of 10.5 and an average observed heterozygosity of 0.801.From the alleles,111 individuals?55.5%of the total number of progeny?and 32 individuals were identified as the progeny of‘Jinsi 4'and other male with a confidence interval of 95%,respectively.and no progeny resulting from self-pollination of‘Dongzao'was detected.A new cross population provides for the construction of genetic linkage map and QTL mapping for jujubeTwo high-density genetic linkage maps were constructed by Joinmap5.0 using SNP marker developed by GBS in the selected 103 F₁populations based on the whole genome sequencing data of Z.jujuba‘Dongzao'and Z.jujuba‘Junzao',respectively.The genetic linkage map named‘D-map'based on reference genome of Z.jujuba‘Dongzao'consists of3678 markers ordered in 12 linkage groups,defining 939.23 c M of total map distance.The average distance between adjacent markers was 0.26 c M.Among the 12 LGs,LG2 was the largest group,with a genetic distance of 92.87 c M and 334 markers.LG11 was the shortest group with 306 markers and spanning 56.97 c M.The average marker interval ranged from0.19 to 0.28 c M.The‘D-map'anchored 324Mb?74%?of scaffolds from the sequenced Z.jujuba“Dongzao”genome.The second genetic linkage map named‘J-map'based on reference genome of Z.jujuba‘Jongzao'consists of 5786 markers ordered in 12 linkage groups,defining 2,167.5 c M of total map distance.The average distance between adjacent markers was 0.358 c M.Among the 12 LGs,LG11 was the largest group,with a genetic distance of 318.5 c M and 3,005 markers.LG07 was the shortest group with 969 markers and spanning 57.68 c M.The average marker interval ranged from 0.24 to 0.48 c M,The genetic map anchored 301Mb?85.7%?of scaffolds from the sequenced Z.jujuba“Junzao”genome.They provided a tool for linkage study of quantitative characters.The leaf length,leaf width,leaf area,leaf shape index,specific leaf weight,chlorophyll and needle traits of F₁population were evaluated in 2016,2017,and 2018.Single fruit weight,fruit transverse diameter,fruit longitudinal diameter,fruit shape index,soluble solids,VC,total sugar,total acid,sugar-acid ratio and edible rate were evaluated in2018,2019.The phenotypic values of 15 traits?except VC and total sugar?showed a single-peak continuous distribution in the population,which indicated that these phenotypes were quantitative genetic traits controlled by multiple genes.With Map QTL,235 QTLs were detected in 17 traits of leaf?6 traits?,needling?only one?and fruit?10 traits?based on CIM?composite interval mapping?.They were distributed on 12lingkage map of“D-map”,including 64 QTLs for leaf traits,15 QTLs for needling traits,156 QTLs for fruit traits.The number of QTLs for leaf length detected was 8;The QTLs for leaf width were 7;Twelve QTLs for leaf area were detected;For leaf shape index,Seventeen QTLs were found;Specific leaf weight was associated with 7 QTLs in total;Thirteen QTLs were detected for chlorophyll content;Fifteen QTLs of needle were got;Forty-three QTLs were detected for single fruit weight;For fruit transverse diameter,sixteen QTLs were detected;QTLs for fruit longitudinal diameter was 36;The number of QTLs for fruit shape index detected was 9;The QTLs for fruit soluble solid was eleven;Thirteen QTLs for VC were detected;For total sugar,three QTLs were found;For total acid,eight QTLs were detected,For sugar-acid ratio,four QTL detected;For edible rate,13 QTL were identified.One hundred and eight QTLs'LOD>3.5,may be major QTLs.All 235 QTLs detected in six leaf,one needling and ten fruit traits were located on 12linkage groups,The number of QTLs from lg1?lg12 were 42,3,14,12,6,11,7,25,17,4,5and 89,respectively.In total,36 marks were related to QTLs at least two of which were co-located.They distributed on lg1,lg4,lg5,lg8 and lg12,separately,19?lg1?,11?lg4?,2?lg5?,8?lg8?and 41?lg12?.Genetic analysis of 10 fruit characters,a large genetic variation in all traits.The fruit size declined.The content of soluble solids was higher than the mean value of parents,the super parent ratio of VC and total acid was higher.There are also a little of plants superior to their parents in the progenies with declining traits,showing certain heterosis.The single fruit weight,sugar to acid ratio,total sugar,soluble solids,fruit longitudinal diameter were selected as principal component from 10 fruit traits with Principal Component Analysis?PCA?,and the cumulative contribution rate was 89.85%.According to the comprehensive scores of principal components,10 individual plants with excellent comprehensive traits were selected:j-48,j-163,j-47,j-58,j-26,j-49,j-127,j-57,j-32,j-35.Further evaluation,j-47 and j-127 were superior individual plant to be selected.Their flesh is compact,juicy,crispy,sweet and sour without residue,and has the characteristics of excellent fresh jujube.Grafting identification and multi-point regional test will be carried out in futureIn conclusion,a high-density genetic linkage map construction and the QTL location for leaf,needle and fruit related agronomic traits provide useful exploration and reference for Chinese jujube genetic breeding and molecular marker assisted selection.