| ABSTRACT Pumpkin is an important melon vegetable crop in the Cucurbitaceae family.It is deeply loved by people because of its rich nutrition and sweet taste.Powdery mildew is one of the most common diseases in pumpkin and other cucurbit crops.It can seriously affect plant photosynthesis and nutrient transportation,resulting in a serious decline in their yield and quality.The short vine trait is a very important and excellent agronomic trait.Because short vine materials can save space during the cultivation process,facilitate management,increase light transmittance and planting density,which contributes to the increase of plant yield and quality.However,the short vine materials in pumpkin cultivars in our country are still deficient.In addition,the size and thousand-grain weight of pumpkin seeds are also important economic traits.Therefore,in this study,a pumpkin genetic map was first constructed using the Cucurbita pepo inbred lines 379 and 296 as parents.Then,the QTL mapping of pumpkin powdery mildew resistance,plant height and seed-related traits was carried out,which will not only be of benefit to the genetic analysis of these traits,but also provide a reference for the molecular marker-assisted breeding in pumpkin.The specific results are as follows:1.306 pairs of polymorphic SSR primers were obtained from the 1437 SSR primers developed by our ourselves.Then,we analysed the genotype of 181 F2 individual plants by these polymorphic primers,and constructed a genetic linkage map including 20 linkage groups.In the map,each linkage group was located on the corresponding chromosome;the total length and the average distance were 3988.32cM,13.03cM,respectively;the length of each linkage group varied from 102.57 to 299.68cM;the marker number in each linkage group is 11-25,and the average distance for each linkage group is between 6.84 and 24.86cM.Moreover,we found the 9th linkage group(Chr9)was the longest(299.68cM),with 25 markers and an average distance of 11.99cM.While,the linkage group No.20(Chr20)has the shortest linkage length(102.57cM),with 15 markers and an average distance of 6.84cM.The results of collinearity analysis showed that the markers were normally distributed on this genetic map,and well covered the reference genome of pumpkin.In addition,the chi-square test showed only 7.84%markers had segregation distortion.All these results revealed that the genetic map we constructed could be used for the next QTL mapping.2.Through the morphology observation of the pumpkin powdery mildew pathogen,we preliminarily determined that the pathogen should belong to the Sphaerotheca fuliginea.By the homology comparison of gene sequences,phylogenetic tree analysis and identification analysis with 13 melon internationally recognized hosts,the pathogen was further classified into the physiological race 2F in Sphaerotheca fuliginea.3.The powdery mildew incidence in F2 population showed a continuous and typical normal distribution,indicating that pumpkin powdery mildew is a quantitative trait.Through QTL mapping,a total of 4 powdery mildew resistance sites were identified.The contribution rate of the single QTL locus was 2.99%-7.37%,and the cumulative contribution rate was 1 8.95%.Among them,the 3 QTL loci with lower contribution rates are located in the linkage groups 5,6,and 9,respectively,and their contribution rates were 3.84%,3.72%,and 4.02%,respectively,and LOD values were 3.43,3.81,and 2.99,respectively.The QTL locus with the largest LOD value(13.55)and the highest contribution rate(7.37%)was located in the 10th linkage group.Further analysis revealed that its physical position was from 2345929bp to 2774957bp on the Chr10.From our results,we speculated that it should be the most important QTL locus for the resistance to powdery mildew in pumpkin.4.Through QTL mapping,a total of 2 QTL loci related to pumpkin plant height traits were identified.They were located on the No.1 and No.10 linkage groups,and their cumulative contribution rate reached to 21.69%.Among them,the linkage group No.10 had the highest contribution rate(19.39%),and its LOD value was 50.53.The physical location analysis showed that its physical position was 432976bp-1437477bp on the Chr10,and the region size was 1004501 bp.we thought that it should be the most important QTL locus for the regulation of the short vine traits in pumpkin.5.Through QTL mapping,this study also identified 10 QTL loci related to pumpkin seed traits,including 1 QTL loci related to the seed length,3 QTL loci related to the seed width,and 1 QTL loci related to the seed shape index,and 5 QTL loci for the seed thousand-seed weight.Further analysis revealed that the QTL loci related to the seed length were located between the two markers SSR005003 and SSR005189 in the second linkage group,with a LOD value of 2.97 and a contribution rate of 9.73%;3 QTL loci related to the seed width are located in the linkage groups 9,12,and 15,respectively,and their LOD values were 4.14,5.03,and 2.54,respectively,and their cumulative contribution rate reached to 32.27%;the QTL locus related to the seed shape index was located between SSR016456 and SSR016525 in the linkage group No.9,and its LOD value was 2.73,and the contribution rate was 9.85%;the QTL loci related to thousand-grain weight were located in the linkage groups 1,3,12,13,and 17,respectively,and their LOD values were 2.61,3.52,2.90,2.53,and 4,respectively,and their cumulative contribution rate was 24.44%. |
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