The Fine Mapping Of Major-Effect QTL Parth2.1 Controling Parthenocarpy And Primary Mapping Of Fruit Tip Trait In Cucumber(Cucumis Sativus L.)

Fruit-related trait is an important commodity trait in cucumber(Cucumis sativus L.),which is closely related to the cucumber quality and grade classification and the market value.Therefore,research of fruit-related traits are critical to cucumber breeding.Parthenocarpy is an important agronomic trait significantly related to fruit quality and yield.Parthenocarpic cucumber can provide stable fruit-bearing ability under environmental factors of low temperature,high humidity or non-pollination.Parthenocarpic fruit is more fleshier and firmer and has a shelf life longer than seeded fruits.Thus,it is significant important to identify the parthenocarpic genes and molecular markers for the breeding and improvement of cucumber parthenocarpy.The fruit tip shape is an important traits which is closely related to the appearance and commodity quality.However,the inheritance of fruit tip is not clear.So,inheritance of fruit tip shape is critical to cucumber breeding.In this study,Fine-mapping of Parth2.1,which was a major-effect QTL conditioning in preliminary mapping of parthenocarpy in the laboratory’s previous work,were performed by screening newly developed InDel marker and single segment substitution lines segregations population.Candidate genes of Parth2.1 were analyzed using re-sequencing,RNA-seq and Cucumber genome database data Classification of fruit tip was performed by 200 cucumber core germplasm resources.The inheritance and preliminary mapping of fruit tip shape were performed by phenotype data and linkage map of F2:3 segregation populations between blunt round fruit tip and sharp round fruit tip,and F2:6 segregation populations between oval round fruit tip and sharp round fruit tip.Furthermore,The fruit tip trait-related QTLs were compared with other fruit QTLs of previous work.The main conclusions are as follow.1.Fine-mapping of Parth2.1 controlling parthnocarpy and associated candidate gene1 Single segment substitution lines segregation population of Parth2.1 were QTL that controlled parthenocarpic fruit set,but did not controlled fruit expanding.The separation of parthenocarpy were both found in the BC3S1 segregation population,which fit to the expected 1 parthenocarpic fruit abortion/3parthenocarpic fruit set segregating ratio in the Chi-square test.These results suggested that the parthenocarpic fruit set is controlled by a single recessive gene.2 A linkage map containing 22 molecular markers was constructed with JoinMap4.0 software by screening 165 InDel primers from two parents re-sequencing,the total length of which was 13.0 cM and average distance between two markers was 0.59 cM.Parth2.1 was mapped within Indel-16Y-46 and Indel-T-8 in linkage map and mapped within the interval of 4.99-5.17 Mb on chromosome 2 of physical map.3 All genes within 181kb of Parth2.1 were analyzed using re-sequencing,RNA-seq and Cucumber genome database data.There were 9 genes in this region based on Cucumber genome database data.Csa2G061570,Csa2G061580,Csa2G061590,Csa2G061600,Csa2G062620 were considered as candidate genes for Parth2.1 based on re-sequencing and RNA-seq date.Candidate genes of Csa2G061570,Csa2G061590,Csa2G061600,Csa2G062620 contained the polymorphic SNPs/Indels in coding sequence region that led to missense or frameshift mutations based on the re-sequencing data.Candidate genes of Csa2G061580,Csa2G061600 were differentially expressed between parthenocapic fruit of EC1 and abortive fruit of 8419s-1 based on the transcriptome data.4 The veracity of Indel-16Y-46 closely linked with parthenocarpic fruit set will play an important role in marker-assisted selection(MAS)for cucumber breeding program of parthenocarpy.2 The inheritance and preliminary mapping of fruit tip shape1 Classification of fruit tip were divided into blunt round,oval round and sharp Fruit tip shape were significant classified as three different grade corresponding to BFT,OFT and SFT by 200 different ecological types of cucumber core germplasm resources.The fruit tip angel and fruit tip index of BFT were vary between 150 and175°,2.5 and 3.5,respectively.The fruit tip angel and fruit tip index of OFT were range between 125 and 150°,2.1 and 2.5,respectively.The fruit tip angel and fruit tip index of SFT were change between 100 and 125°,1.4 and 2.0,respectively.2.The growth characteristics fruit tip diameter(FTD),fruit tip length(FTL)were accord with the typical single "S-shape" growth curve during 0 to 40 days post anthesis(DPA).There was no significant difference in FTD and FTL between EC1,IL52 and 8419s-1 at 0 DPA,but the longitudinal paraffin sections of ovary of EC 1,IL52 and 8419s-1 showed that there was no significant difference in the cell size of FTD and FTL on ODPA,while the cell number of FTD and FTL showed no significant difference.3.Results from ANOVA revealed significant difference between families,seasons and familyx season interaction of fruit tip.The heritability estimate of mean FTD was as high as 76.2%and 88.0%in F2:3family and F2:6family,respectively.The heritability estimate of mean FTL was as high as 71.9%and 88.7%in F2:3family and F2:6family,respectively.The heritability estimate of mean FTI was as high as 74.2%and 70.9%in F2:3family and F2:6family,respectively.The frequency distribution of DFT,DFL and DFI were a normal distribution in the F2:3family and F2:6family.These results indicate that fruit tip shape was a quantitative trait significantly affected by environment and genotype of families in different seasons.4.In total,25 fruit tip traits related QTLs were identified in F2:3 segregation populations and F2:6 segregation populations performed by phenotype data and linkage map of F2:3 segregation populations between blunt round fruit tip and sharp round fruit tip,and F2:6 segregation populations between oval round fruit tip and sharp round fruit tip.Ft3.1,Ft3.2,Ft4.1and Ft6.1 were stable QTLs identified in multiply season,of which Ft4.1and Ft6.1 were stable major-effect QTLs that explain 11.0%to 32.6%of the phenotypic variance and were also participate in the regulation of fruit shape traits such as fruit length and fruit transverse diameter,fruit stalk.Furthermore,typical parallels across all genotypes were observed indicating that there was strong dominant epistatic interaction between Ft4.1 and Ft6.1.