QTL Analysis Of Main Quality Traits In Melon Fruit

Melon（Cucumis melo L.）is an important vegetable crop of Cucurbitaceae,widely grown in many countries including China.Melon fruit has great variability in morphology,soluble solid content,flesh firmness,pulp color and exocarp firmness.Melon is popular for its sweet taste and high nutritional value.Soluble solid content,flesh firmness and exocarp firmness are the sensory qualities of melon fruit and are also very useful harvest indicators.It has always been the pursuit of breeders to cultivate sweet and delicious melon varieties with moderate taste and storage and transportation resistance.In this study,M4-5 with low hardness and low soluble solid content was used as the female parent,M1-15 with high hardness and high soluble solid content was used as the male parent,and the F₂ population obtained from both parents was used as the test material,and QTL mapping analysis was used.Strategy,high-throughput sequencing of parents to obtain SNP information,use CAPS molecular markers derived from SNP to construct genetic linkage map,conduct QTL analysis on soluble solid content of melon fruit,peel and fruit firmness;for soluble solid content,in the second year,a larger F₂ population was used to conduct QTL analysis to verify its accuracy and stability.The main research results of this experiment are as follows:（1）According to the resequencing results,the SNP sites were excavated and converted into CAPS markers by combining the restriction site information of three restriction endonucleases（Eco R I,Hind III,Bam H I）.A total of 290 pairs of CAPS markers were designed,parents and F₁were screened for polymorphisms and 116 pairs of CAPS markers with polymorphisms were obtained.116 pairs of CAPS markers were used to genotype the F₂ generation segregation population,and a genetic linkage map was constructed by QTL Ici Mapping（v4.0）.The genetic linkage map consists of 12 linkage groups,the total genetic distance is 1414.88 c M,and the average genetic distance is 12.20 c M.（2）Six QTLs related to main fruit quality traits were detected in 2021:the QTLs related to soluble solids content were SSC6.1 and SSC11.1;the QTLs related to flesh firmness were FF3.1,FF3.2 and FF7.1;the QTL related to exocarp firmness was EF12.1,located on chromosome 3,6,7,11 and 12 respectively,two QTLs located on chromosome 3,and one QTL on chromosome 6,7,11and 12 respectively.In addition to the negative additive effect of QTLs for soluble solids content,the additive effects of the other QTLs were all positive,and the phenotypic variation rate was 4.89%-16.32%.In 2022,a larger F₂ population was used to conduct QTL analysis on soluble solid content,and it was still detected at a identical position on chromosome 6,with an LOD value of 10.19 and a phenotypic variation rate of 12.30%.（3）At the same time,the genotype-phenotype correlation of the F₂ population was analyzed using the three CAPS markers flanking the SSC6.1 location interval,which verified that the genotype of the F₂ population was highly correlated with the soluble solid content,proving the accuracy of the QTL results.And the CAPS marker was added to the interval where SSC6.1 was located,and the genes in the narrowed interval were screened,and MELO3C016609.2 was found,annotated as pectinesterase which was speculated to be a candidate gene that may control the soluble solid content of melon fruit.