Genetic Analysis And QTL Mapping Of Fruit Stalk Length In Cucumber (Cucumis Sativus.L)

Cucumber (Cucumis sativus L.) is an climbing annual herbaceous plants belonging to cucurbitaceae.It is one of the important vegetables, which has a closely relation with people’s life. The fruit stalk length of cucumber is one of the most important traits, which affect the quality and economical value of cucumber. Regardless of appearance or edible rate, the shorter fruit stalk length of cucumber the higher value of it’s seized of. The related research and report of fruit stalk length in cucumber is still less and not deep enough. In view of the progress of genetic improvement of fruit stalk length traits in cucumber is slow, therefore, to carry out the genetic mechanism and finding the key genes of fruit stalk length in cucumber have important theoretical and applied value.Cucumber inbred lines D8 with short stalk length and JIN5-508 with long stalk length were used as the experiment materials for genetic analysis and gene mapping for fruit stalk length in this study. The six generation of the population derived from D8×JIN5-508 was applied to separate and analysis the genetic system of fruit stalk length in cucumber. F2 population was used as the mapping population, the genetic linkage map was constructed with SSR markers, and fruit stalk length related QTL ananlysis was performed with composite interval mapping(CIM). Based on this, the SNPs site was excavated in the main effect QTL based on resequencing of parents and convert its to dCAPS markers. Expanding F2 (1273 individuals in total) population was used to construct the fine mapping and obtained the linkage markers related to the fruit stalk length in cucumber. The main results are as follows:1. The fruit stalk length of cucumber was controlled by one pair of additive-dominant (same) major gene plus additive-dominant polygenic model hybrid model (D-3). The heritability of major gene in F2 population is 14.99%, the heritability of polygene is 37.84%, and the environmental effect is 47.17%. The above results showed that, high generation selection is good for fruit stalk length breeding in cucumber.2. The genetic map consisted of seven linkage group were carried out on 160 pairs of SSR marker which were recorded in 121 F2 population. The length of map was 640 cM.QTL analysis identified 2 QTLs, distributing on chromosomes 4 and 7, named Fs14-1 and Fs17-1. Fs14-1 locating between SSR29712 and SSR10368, having LOD score of 6.5%, explaining 14.58% of variation was the major effect QTL, and its genetic distance was 7 cM; Fsl7-1 locating between SSR15322 and SSR21743, having LOD score of 3.8, explaining 5.6% of variation was the minor effect QTL, and its genetic distance was 8 cM.3. D8 and JIN5-508 were resequenced, and 115 SNP loci were obtained between the SSR29712 and SSR10368 in the major effect QTL Fs14-1. Convert SNP to dCAPS markers and 12 pairs was showed polymorphism in parent lines. The fruit stalk length of cucumber was fine mapped between SNP16179817 and SNP 16527325, at a 347.5 kbp physical distance. There were 22 genes.4. Od,6d and 12d fruit stalk of D8 and JIN5-508 were used as materials to investigate differences in candidate genes. From the qRT-PCR resuits, we found that the expression levels of Csa4M431890.1 (microtubule-associated protein 70-2)> Csa4M436980.1 (two-component response regulator ARR9) and Csa4M430880.1 (alpha-glucosidase YihQ) genes in fruit stalk exhibited obvious higher in D8 than JIN5-508. Csa4M432460.1 (phosphatidylinositol 4-phosphate 5-kinase 5) genes in fruit stalk exhibited obvious higher JIN5-508 in than D8.Therefore, Csa4M431890.1、Csa4M436980.1、Csa4M430880.1 and Csa4M432460.1 may be the key genes that determine the formation of fruit stalk length in cucumber.