Cucurbita pepo is a cucurbit with growing economic importance worldwide. Zucchini morphotype is the most important within this highly variable species. Recently, transcriptome and Simple Sequence Repeat (SSR)- and Single Nucleotide Polymorphism (SNP)-based medium density maps have been reported, however further genomic tools are needed for efficient molecular breeding in the species. Our objective is to combine currently available complete transcriptomes and the Zucchini genome sequence with high throughput genotyping methods, mapping population development and extensive phenotyping to facilitate the advance of genomic research in this species. We report the Genotyping-by-sequencing analysis of a RIL population developed from the inter subspecific cross Zucchini x Scallop (ssp. pepo x ssp. ovifera). Several thousands of SNP markers were identified and genotyped, followed by the construction of a high-density linkage map based on 7,718 SNPs (average of 386 markers/linkage group) covering 2,817.6 cM of the whole genome, which is a great improvement with respect to previous maps. A QTL analysis was performed using phenotypic data obtained from the RIL population from three environments. In total, 48 consistent QTLs for vine, flowering and fruit quality traits were detected on the basis of a multiple-environment analysis, distributed in 33 independent positions in 15 LGs, and each QTL explained 1.5–62.9% of the phenotypic variance. Eight major QTLs, which could explain greater than 20% of the phenotypic variation were detected and the underlying candidate genes identified. Here we report the first SNP saturated map in the species, anchored to the physical map. Additionally, several consistent QTLs related to early flowering, fruit shape and length, and rind and flesh color are reported as well as candidate genes for them. This information will enhance molecular breeding in C. pepo and will assist the gene cloning underlying the studied QTLs, helping to reveal the genetic basis of the studied processes in squash.

Background: Cucurbita pepois a member of the Cucurbitaceae family, the second- most important horticultural family in terms of economic importance after Solanaceae. The "summer squash" types, including Zucchini and Scallop, rank among the highest-valued vegetables worldwide. There are few genomic tools available for this species.The firstCucurbitatranscriptome, along with a large collection of Single Nucleotide Polymorphisms (SNP), was recently generated using massive sequencing. A set of 384 SNP was selected to generate an Illumina GoldenGate assay in order to construct the first SNP-based genetic map ofCucurbitaand map quantitative traitloci(QTL).Results: We herein present the construction of the first SNP-based genetic map ofCucurbita pepousing a population derived from the cross of two varieties with contrasting phenotypes, representing the main cultivar groups of the species' two subspecies: Zucchini (subsp.pepo) × Scallop (subsp.ovifera). The mapping population was genotyped with 384 SNP, a set of selected EST-SNP identifiedin silicoafter massive sequencing of the transcriptomes of both parents, using the Illumina GoldenGate platform. The global success rate of the assay was higher than 85%. In total, 304 SNP were mapped, along with 11 SSR from a previous map, giving a map density of 5.56 cM/marker. This map was used to infer syntenic relationships betweenC. pepoand cucumber and to successfully map QTL that control plant, flowering and fruit traits that are of benefit to squash breeding. The QTL effects were validated in backcross populations.Conclusion: Our results show that massive sequencing in different genotypes is an excellent tool for SNP discovery, and that the Illumina GoldenGate platform can be successfully applied to constructing genetic maps and performing QTL analysis inCucurbita. This is the first SNP-based genetic map in theCucurbitagenus and is an invaluable new tool for biological research, especially considering that most of these markers are located in the coding regions of genes involved in different physiological processes. The platform will also be useful for future mapping and diversity studies, and will be essential in order to accelerate the process of breeding new and better-adapted squash varieties.

Background: There are few genomic tools available in melon (Cucumis melo L.), a member of the Cucurbitaceae, despite its importance as a crop. Among these tools, genetic maps have been constructed mainly using marker types such as simple sequence repeats (SSR), restriction fragment length polymorphisms (RFLP) and amplified fragment length polymorphisms (AFLP) in different mapping populations. There is a growing need for saturating the genetic map with single nucleotide polymorphisms (SNP), more amenable for high throughput analysis, especially if these markers are located in gene coding regions, to provide functional markers. Expressed sequence tags (ESTs) from melon are available in public databases, and resequencing ESTs or validating SNPs detected in silico are excellent ways to discover SNPs. Results: EST-based SNPs were discovered after resequencing ESTs between the parental lines of the PI 161375 (SC) × 'Piel de sapo' (PS) genetic map or using in silico SNP information from EST databases. In total 200 EST-based SNPs were mapped in the melon genetic map using a bin-mapping strategy, increasing the map density to 2.35 cM/marker. A subset of 45 SNPs was used to study variation in a panel of 48 melon accessions covering a wide range of the genetic diversity of the species. SNP analysis correctly reflected the genetic relationships compared with other marker systems, being able to distinguish all the accessions and cultivars. Conclusion: This is the first example of a genetic map in a cucurbit species that includes a major set of SNP markers discovered using ESTs. The PI 161375 × 'Piel de sapo' melon genetic map has around 700 markers, of which more than 500 are gene-based markers (SNP, RFLP and SSR). This genetic map will be a central tool for the construction of the melon physical map, the step prior to sequencing the complete genome. Using the set of SNP markers, it was possible to define the genetic relationships within a collection of forty-eight melon accessions as efficiently as with SSR markers, and these markers may also be useful for cultivar identification in Occidental melon varieties.

Background: Melon (Cucumis melo L.) is a highly diverse species that is cultivated worldwide. Recent advances in massively parallel sequencing have begun to allow the study of nucleotide diversity in this species. The Sanger method combined with medium-throughput 454 technology were used in a previous study to analyze the genetic diversity of germplasm representing 3 botanical varieties, yielding a collection of about 40,000 SNPs distributed in 14,000 unigenes. However, the usefulness of this resource is limited as the sequenced genotypes do not represent the whole diversity of the species, which is divided into two subspecies with many botanical varieties variable in plant, flowering, and fruit traits, as well as in stress response. As a first step to extensively document levels and patterns of nucleotide variability across the species, we used the high-throughput SOLiD™ system to resequence the transcriptomes of a set of 67 genotypes that had previously been selected from a core collection representing the extant variation of the entire species. Results: The deep transcriptome resequencing of all of the genotypes, grouped into 8 pools (wild African agrestis, Asian agrestis and acidulus, exotic Far Eastern conomon, Indian momordica and Asian dudaim and flexuosus, commercial cantalupensis, subsp. melo Asian and European landraces, Spanish inodorus landraces, and Piel de Sapo breeding lines) yielded about 300 M reads. Short reads were mapped to the recently generated draft genome assembly of the DHL line Piel de Sapo (inodorus) x Songwhan Charmi (conomon) and to a new version of melon transcriptome. Regions with at least 6X coverage were used in SNV calling, generating a melon collection with 303,883 variants. These SNVs were dispersed across the entire C. melo genome, and distributed in 15,064 annotated genes. The number and variability of in silico SNVs differed considerably between pools. Our finding of higher genomic diversity in wild and exotic agrestis melons from India and Africa as compared to commercial cultivars, cultigens and landraces from Eastern Europe, Western Asia and the Mediterranean basin is consistent with the evolutionary history proposed for the species. Group-specific SNVs that will be useful in introgression programs were also detected. In a sample of 143 selected putative SNPs, we verified 93% of the polymorphisms in a panel of 78 genotypes. Conclusions: This study provides the first comprehensive resequencing data for wild, exotic, and cultivated (landraces and commercial) melon transcriptomes, yielding the largest melon SNP collection available to date and representing a notable sample of the species diversity. This data provides a valuable resource for creating a catalog of allelic variants of melon genes and it will aid in future in-depth studies of population genetics, marker-assisted breeding, and gene identification aimed at developing improved varieties.