Background 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.ResultsWe 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.ConclusionsHere 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3439-y) contains supplementary material, which is available to authorized users.

reported to be useful for predicting shoot resistance, were performed, and plants were scored using a scale of disease severity. The average disease severity was calculated for each accession and was used to cluster the accession in five reaction classes. The screening revealed that sources of natural resistance to this fungus are limited. However, seedlings of seven accessions of different botanic groups displayed a resistant response to the stem inoculation, one cantaloup from Israel, one conomon accession from Korea, two wild agrestis and one acidulus from Africa, and two dudaim accessions from Middle East. The response of the F1 progenies varied from susceptibility to high resistance, the latter in progenies from the two agrestis wild types. These results suggest differences in the genetic basis of the resistance in the different selected sources. The resistant accessions are suggested to be screened under field conditions to confirm the level of resistance at adult plant stage and under stressful conditions.

Podosphaera xanthii is the most important causal agent of powdery mildew in melon, a crop ranked within the most economically important species worldwide. The best strategy to face this fungus disease, which causes important production losses, is the development of genetically resistant cultivars. Genetic breeding programmes require sources of resistance, and a few ones have been reported in melon, mostly in Momordica and Acidulus horticultural groups. However, the existence of many races that reduces the durability of the resistance makes necessary to find new resistant genotypes with different genetic backgrounds. In this work, Brazilian germplasm, together with a set of Indian landraces, and the COMAV's (Institute for the Conservation and Breeding of Agricultural Biodiversity) melon core collection, representing the whole variability of the species, were assessed for resistance against some common races in Spain and Brazil and genotyped with a 123-SNP (single nucleotide polymorphisms) genotyping platform to study the molecular relationships of the resistant accessions. In the first experiment, carried out in Valencia (Spain) in 2013, seventy-nine melon accessions were evaluated using artificial inoculation. Five accessions selected as resistant were also evaluated against races 1, 3, and 5 in Mossoró (Brazil, 2015) and against race 3.5 in Valencia (2016) under greenhouse conditions, and under four field conditions in Brazil. The accessions, AL-1, BA-3, CE-3, and RN-2, within the Brazilian collection, presented resistance against all the races of P. xanthii assayed in all conditions tested. AL-1, CE-3 and RN-2 were molecularly more similar to wild agrestis and Acidulus melons from Asia and Africa, while BA-3 grouped with Momordica types. Molecular analysis also confirmed that these new Brazilian sources of resistance differ from those previously reported, constituting interesting materials to encourage genetic breeding programmes, especially in Brazil and Spain.