QTL Mapping Of Seed Traits In Cucurbita Maxima

Cucurbita maxima is one of the important cultivated varieties of Cucurbitaceae Cucurbita.It is an important horticultural cash crop for both vegetable oil and vegetable,and it is also widely cultivated worldwide.Our country is a big pumpkin consumer and large pumpkin producing country.The pumpkin industry plays an important role in the national economy and modern urban agriculture.pumpkin seeds which contain rich nutrients are popular with consumers.The sedd size and 100 seed weight are important indexes to evaluate the commercial value of pumpkin seeds.Therefore,mapping of seed length and width can effectively improve the breeding efficiency of Cucurbita maxima.An F₂ population driven from a cross between the Cucurbita maxima inbred lines’2013-12’and’9-6’was used for QTL mapping analysis of seed traits in our experiment.Previous studies had mapped seed length and seed width QTLs on chromosome 6.To further verify the localization results of seed length and width,150 F₂ invividuals were scanned with CAPS and In Del markers on chromosome 6.QTLs of seed length and width were mapped based on genotype data of F₂and phenotypic data of F₂ population and F_2:3 family.Then,the candidate genes mapped in the QTL region were screened according to gene annotation and amino acid sequence alignment between parents.The main findings were as follows:（1）Most of the phenotypic data of seed length,seed width,seed aspect ratio,100-seed weight and seed number per fruit,the 5 seed traits were all quantitative traits.（2）According to the correlation analysis between the 5 traits of the F_2:3 population,it could be seen that the seed length and seed width were significantly positively correlated.The seed aspect ratio and the seed length were positively correlated.The seed aspect ratio and the width were negatively correlated.The 100-seed weight was significantly positively correlated with the seed width and seed length.The seed number per fruit was not correlated with the other four seed traits.（3）Using parental resequencing and Cucurbita maxima genome information,17 CAPS markers and 7 In Del markers were developed on chromosome 6.Among them,9 CAPS markers and2 In Del markers were polymorphic.The polymorphism rate of CAPS markers was 52.94%,and the In Del labeled the polymorphism rate of 28.57%.（4）A genetic linkage map containing 11 molecular markers was constructed on chromosome6 in Cucurbita maxima with a total length of 64.48c M and an average map distance between markers of 5.86 c M.A seed length QTL SL6-1F₂ was identifed between the markers Chr06＿2374213 and Chr06＿3507675（2.37-3.51Mb）with the LOD value was 3.6,which could explain 22.2%of the phenotypic variation.Between the markers Chr06＿1468248 and Chr06＿1929605（1.47-1.93Mb）,a seed width QTL SW6-1F₂ was detected.The QTL could explain 20.8%of the phenotypic variation and the LOD value was 4.8.（5）According to the information of the Cucurbita maxima genome,there are 15 genes in the QTL region of seed length that have non-synonymous SNP mutation sites between the two parents,and 7 genes in the QTL locus of seed width that have non-synonymous SNPs between the two parents.According to the reference genome annotation of Cucurbita Maxima,three candidate genes that may be seed size were selected.Two genes,Cma Ch06G005450.1 of E3 ubiquitin ligase and Cma Ch06G005530.1 of VQ motif,were found with SNPs in the conserved sequences between the two parents.The Cma Ch06G004140.1 gene had a SNP at the C2 N-terminal conserved motif of leucine-rich repeat（LRR）and a SNP at the chromosomal structure maintenance protein conserved motif.of leucine-rich repeat（LRR）The conserved sequences of Cma Ch06G005450.1,Cma Ch06G005530.1 and Cma Ch06G004140.1 all had non-synonymous SNPs between parents,which may affect protein function.It is demonstrated that these three genes were the potential regulators for seed length and seed width.