Construction Of Genetic Linkage Map And Qtl Analysis For Fruit Shape Related Traits In Pumpkin(Cucurbita Pepo L.)

Cucurbita pepo L is one of the Cucurbita species belonging to Cucurbitaceae plant.Cucurbita pepo is an annual vine herb that is widely cultivated in the world,and it is loved by consumers.The shape and size of pumpkin fruit directly affect its commercial value,which is one of the important goals in the good varieties of Cucurbita pepo breeding.In this study,a genetic linkage map was constructed with F₂ population derived from two homozygous inbred lines’X10’and’JIN234’of Cucurbita pepo L.（1）The results showed that the frequency distribution of fruit length,fruit width and fruit shape index of F₂ population was basically in line with normal distribution.It is indicated that these three traits were quantitative which controlled by multiple genes.Fruit length was positively correlated with fruit width and fruit shape index,while fruit width was negatively correlated with fruit shape index.（2）A total of 1589 SSR markers were screened in this study,122 SSR markers with good polymorphism were selected,and these SSR markers could be clearly typed in the F ₂ population.Then,using parental resequencing SNP data,a total of 217 CAPS markers were developed,and126 of them were polymorphic.These markers were clearly typed in the F ₂ population,with a polymorphism rate of about 58%.Taking 93 F₂individuals for QTL mapping,and the genetic linkage analysis baesd on the 248 molecular marker data was conducted using QTL Ici Mapping V4.1 software in this study to draw a genetic linkage map of Cucurbita pepo L.The map had a total of 20 linkage groups,which correspond to 20 chromosomes of pumpkin.The genetic map covered 2256.56 c M with the average genetic distance of 9.17 c M.The linkage group1 was the longest with a total of 220.05 c M,and the linkage group 20 was the shortest with 57.74c M and contained 10 molecular markers.（3）In this study,15 QTLs related to fruit shape were distributed in the linkage groups of 1,2,3,6,7 and 20 according to the phenotype data of F₂ population in 2017 and F_2:3 family in 2018 and2019.A total of 7 QTLs related to fruit length were detected using 3 years data.One of the fruit length QTL Fl3.2 mapped between marker LG3-54510 and marker LG3-756833 in the linkage group 3 was identified in all three years,and the contribution rates were 39.01%,31.89%and40.70%in 3 years,respectively.The fruit length QTL Fl3.1 mapped in linkage group 3 was identified in 2018 and 2019,and the contribution rates were 9.95%and 8.08%in 2018 and 2019.The other five QTLs were all micro-effect QTLs with relatively low contribution rates,and could only be identified in one year.（4）Using 3 years of data,a total of 4 QTLs related to fruit width were detected.One QTL Fw3.1 located in linkage group 3 was identified in 2018 and 2019,and the contribution rates were15.97%and 10.18%in 2018 and 2019,respectively.However,the other three QTLs,Fw7.1,Fw7.2and Fw20.1,could only be detected in one year,and their contribution rates were 18.96%,14.26%and 12.9%,respectively.（5）A total of 4 QTLs related to fruit shape index were detected using 3 years of data.Amo ng these QTLs,the major fruit shape index QTL Fsi3.2 mapped between marker LG3-54510 and marker LG3-756833 in linkage group 3 was identified in all three years,and the contribution rates in 3 year were 44.97%,46.77%and 37.55%,respectively.The other three minor QTLs could only be detected in one year,and showed low contribution rates.