| Chinese jujube(Ziziphus jujuba Mill.)is a dominant fruit tree which is native to China.It is difficult to obtain hybrid progeny germplasm on a large scale,resulting in slow progress in hybrid breeding,and molecular marker-assisted breeding technology is relatively backward compared with other fruit trees.The study of the genetic pattern of jujube flower and fruit traits and the QTL localization are of great application to the selection of hybrid parents and the development of molecularly assisted breeding techniques for jujube.In this study,13 traits,including flower size,pollen,fruit size and nutritional quality,were investigated and determined using the F1-generation segregating population of ’Yuhong’(JMS2,male sterile)× ’ Jiaocheng 5 ’ as the test material.Based on the high-density molecular genetic map constructed in the early stage,we carried out QTL localization studies for each trait;screened single plants with extreme values of fruit size in the hybrid population to build mixed pools of large and small fruits,conducted QTL-seq localization analysis,and performed linkage analysis on the localized intervals to accurate localize QTL for fruit size traits,so as to lay the foundation for mining key genes regulating fruit size.The main results obtained were as follows:1.Five flower-related traits,including flower area,flower diameter,nectar disk diameter,pollen quantity and pollen vigor,were widely segregated in the F1 population of the cross,with coefficients of variation ranging from 8.88% to 50.13%.The two traits of flower diameter and flower area showed moderate inheritance,and pollen volume and pollen vigor tended to be inherited from the parents;The flowers of F1 population plants were pollinated,and the mean values of pollen quantity and pollen activity traits were higher than the mid-parent values in both years,showing a clear superparental inheritance.All five floral traits showed single-peaked normal or skew-normal distribution characteristics,and all were quantitative traits controlled by multiple genes,among which flower diameter,flower area and nectar disk diameter were significant correlated,and pollen quantity and pollen activity were not significantly correlated.Eight fruit traits,including single fruit weight,longitudinal fruit diameter,transverse fruit diameter,fruit shape index,soluble sugar,organic acid,soluble solids,and vitamin C content,also showed extensive segregation,all of which were characterized by single-peaked normal or skew-normal distribution.Presumably,they were quantitative traits controlled by multiple genes,with coefficients of variation ranging from 9.09% to 33.52%.Fruit size tended to be inherited lower,soluble solids performance tended to be inherited higher,and soluble sugars tended to be inherited lower.All eight fruit traits showed single-peaked normal or skew-normal distribution characteristics,and all were quantitative traits controlled by multiple genes,among which single fruit weight,fruit longitudinal diameter and fruit transverse diameter were closely correlated,single fruit weight was not significantly correlated with fruit shape index,and soluble sugar was significantly correlated with soluble solids.2.A total of 54 QTL loci were localized by the MQM mapping method of Map QTL 6.0software,with LOD value ≥ 3.0 as the threshold,including 34 QTL loci for flower size and pollen-related traits,and 20 QTL loci for fruit size and intrinsic quality-related traits.Using LOD value ≥3.5 as the threshold value for QTL effect,a total of 24 active QTL loci were found,including 19 active QTL loci for flower size and pollen-related traits,and 5 active QTL loci for fruit size and intrinsic quality-related traits.Ten overlapping intervals for flower size and one overlapping interval for fruit size were found.3.Fruit size was localized using QTL-seq technique,and candidate intervals were mainly located on chromosomes 1,5 and 10,with the most intervals localized to chromosome 1.Then based on the localization results of QTL-seq technology among the screened 424 SNPs and 164 In Del respectively,the annotation results of ANNOVAR were extracted and 40 candidate genes were selected preferentially,and 37 annotatable candidate genes were found on the date genome.The four genes associated with fruit size growth and development were LOC107428904,LOC107415626,LOC125420708 and LOC107418290,which were screened according to the functional prediction of annotated genes from the NCBI website.4.Combining both QTL localization and QTL-seq techniques,the intervals regulating fruit size were narrowed down to three intervals on chromosome 1,with interval positions of33.74～35.05 Mb,35.11～35.14 Mb,and 38.56～40.54 Mb,with a total interval length of 3.33 Mb,containing 244 genes. |
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