QTL Mapping And Analysis Of Starch And Soluble Solid Content Traits In Pumpkin(Cucurbita Maxima Duch.)

Pumpkin（Cucurbita maxima Duch.）belonged to Cucurbitaceae,Cucurbita annual vine.Pumpkin fruit has a high edible value,medicinal value and health care value.The starch content and soluble solite content of pumpkin fruit are the important quality traits,and together affect th e flavor,taste and nutritional value of the fruit.So high starch content and high soluble solite content are important targets of high-quality pumpkin breeding.In this experiment,the high-generation inbred line’98-2’contained low starch,and low soluble solid content（ssc）,while the high-generation inbred line’312-1’contained high starch and high soluble solid content.These two inbred lines were used as the experimental materials,and the total starch content,starch content of amylopectin,straight amylose content,soluble solid content and water content of mature pumpkin fruit were determined,respectively.Molecular markers were developed across 20 chromosomes using parental resequencing data,and the genetic linkage map was constructed using the polymorphism molecular markers combined with the F₂ population.Genetic analysis and QTL analyses were performed for pumpkin starch and soluble solid content traits.The main findings are as follows:（1）The total starch content,amylopectin content,amylose content,soluble solite content,and water content were determined from mature pumpkin fruits（frui ts after 45 days of pollination）of’98-2’,’312-1’,F₁,F₂.The total starch content,amylopectin content,amylose content,and soluble solid of‘98-2’were significantly lower than that of‘312-1’in fruit.The water content of‘98-2’was significantly higher than that of‘312-1’.The frequency distribution of each trait in the F₂population basically matches the quantitative characteristic inheritance.It is shown that each trait was controlled by multiple genes.Correlation analysis of starch and solubl e solid was performed using F₂ population data.In the total starch content,amylopectin content,amylose content,and soluble solid material content,the relation between each pair of traits was significantly and positively correlated.Water content was significantly negatively correlated with other four traits.（2）A total of 172,161 In Dels was obtained between’98-2’and’312-1’based on resequencing,and 442 indel molecular markers on 20 pairs of chromosomes were designed using Primer premier5 and Primer premier 6 software.Among them,225 In Del molecular markers showed polymorphisms between parents and clear bands in F₂ populations,and the polymorphism rate was51%.With 225 indel molecular markers,the pumpkin genetic map covered 20 linkage groups was constructed using Join Map v4.0 software.The genetic map length is 2783.75c M,and the average distance between markers is 12.37 c M.The length of each linkage group range is from 82.12c M to261.71c M.（3）Based on the genetic map,QTLs for pumpkin fruit starch and soluble solid traits were detected using QTL Ici Mapping v4.2 software.A total of 12 QTLs were detected on the linkage groups 2,3,4,11 and 20.Two QTLs for total starch content,qsta4.1,qsta11.1,were detected with a contribution rate of 10.91%and 2.57%.Two QTLs for amylopectin content,qalp4.1,qalp11.1,were detected with a contribution rate of 12.49%and 2.43%.Two QTLs for amylose content,qals4.1,qals11.1,were detected with a contribution rate of 5.57%and 3.61%.and QTLs for soluble solid content,qssc2.1,qssc4.1,were detected with a contribution rate of 3.57%and23.07%.Four QTLs for water content,qwc2.1,qwc3.1,qwc4.1 and qwc20.1,were detected with a contribution rate of 4.70%,4.32%,21.34%and 2.75%.Among them,the qsta4.1,qalp4.1,qssc4.1,qwc4.1 were the main effect of QTLs.