Two populations [an F(2) and a set of 77 double haploid lines (DHLs)] developed from a cross between a 'Piel de Sapo' cultivar (PS) and the exotic Korean accession PI 161375 were used to detect QTLs involved in melon fruit quality traits: earliness (EA), fruit shape (FS), fruit weight (FW) and sugar content (SSC); and loci involved in the colour traits: external colour (ECOL) and flesh colour (FC). High variation was found, showing transgressive segregations for all traits. The highest correlation among experiments was observed for FS and the lowest for FW and SSC. Correlations among traits within experiments were, in general, not significant. QTL analysis, performed by Composite Interval Mapping, allowed the detection of nine QTLs for EA, eight for FS, six for FW and five for SSC. Major QTLs ( R(2)>25%) were detected for all traits. QTLs for different traits were no clearly co-localised, suggesting low pleiotropic effects at QTLs. Sixty-one per cent of them were detected in two or more experiments. QTLs for FS were detected in more trials than QTLs for FW and SSC, confirming that FS is under highly hereditable polygenic control. ECOL segregated as yellow:green in both experimental populations. The genetic control of ECOL was found to be complex, probably involving more than two loci with epistatic interactions. One of these loci was mapped on linkage group 9, but the other loci could not be clearly resolved. FC segregated as white:green:orange. The locus responsible for the green FC was mapped on linkage group 1, and it was proposed to correspond to the previously described locus gf. The genetic control of orange FC was complex: two loci in linkage groups 2 and 12 were associated with orange flesh, but larger population sizes would be necessary to elucidate completely the genetic control of orange flesh in this cross. Exotic alleles from PI161375 showed beneficial effects on EA, FW and SSC, indicating the usefulness of PI 161375 as a new source of genetic variability to improve European and American cultivars.

A set of 118 simple sequence repeat (SSR) markers has been developed in melon from two different sources: genomic libraries (gSSR) and expressed sequence-tag (EST) databases (EST-SSR). Forty-nine percent of the markers showed polymorphism between the 'Piel de Sapo' (PS) and PI161375 melon genotypes used as parents for the mapping populations. Similar polymorphism levels were found in gSSR (51.2%) and EST-SSR (45.5%). Two populations, F2 and a set of double haploid lines (DHLs), developed from the same parent genotypes were used for map construction. Twenty-three SSRs and 79 restriction fragment length polymorphisms (RFLPs), evenly distributed through the melon genome, were used to anchor the maps of both populations. Ten cucumber SSRs, 41 gSSRs, 16 EST-SSR, three single nucleotide polymorphism (SNP) markers, and the Nsv locus were added in the DHL population. The maps developed in the F2 and DHL populations were co-linear, with similar lengths, except in linkage groups G1, G9, and G10. There was segregation distortion in a higher proportion of markers in the DHL population compared with the F2, probably caused by selection during the construction of DHLs through in vitro culture. After map merging, a composite genetic map was obtained including 327 transferable markers: 226 RFLPs, 97 SSRs, three SNPs, and the Nsv locus. The map length is 1,021 cM, distributed in 12 linkage groups, and map density is 3.11 cM/marker. SSR markers alone cover nearly 80% of the map length. This map is proposed as a basis for a framework melon map to be merged with other maps and as an anchor point for map comparison between species of the Cucurbitaceae family.

Loci on LGIV, VI, and VIII of melon genome are involved in the control of fruit domestication-related traits and they are candidate to have played a role in the domestication of the crop. The fruit of wild melons is very small (20-50 g) without edible pulp, contrasting with the large size and high pulp content of cultivated melon fruits. An analysis of quantitative trait loci (QTL) controlling fruit morphology domestication-related traits was carried out using an in vitro maintained F population from the cross between the Indian wild melon "Trigonus" and the western elite cultivar 'Piel de Sapo'. Twenty-seven QTL were identified in at least two out of the three field trials. Six of them were also being detected in BC1 and BC3 populations derived from the same cross. Ten of them were related to fruit morphological traits, 12 to fruit size characters, and 5 to pulp content. The Trigonus alleles decreased the value of the characters, except for the QTL at andromonoecious gene at linkage group (LG) II, and the QTL for pulp content at LGV. QTL genotypes accounted for a considerable degree of the total phenotypic variation, reaching up to 46%. Around 66% of the QTL showed additive gene action, 19% exhibited dominance, and 25% consisted of overdominance. The regions on LGIV, VI, and VIII included the QTL with more consistent and strong effects on domestication-related traits. QTLs on those regions were validated in BC2S1, BC2S2, and BC3 families, with "Trigonus" allele decreasing the fruit morphological traits in all cases. The validated QTL could represent loci involved in melon domestication, although further experiments as genomic variation studies across wild and cultivated genotypes would be necessary to confirm this hypothesis.

A new and simple protocol for androgenesis in bell pepper is described. The initial medium, a modification of Nitsch and Nitsch's H medium, consisted of a two-phase system of semi-solid and liquid medium and contained maltose as carbon source. The total number of embryos formed was greater with maltose at 40 g·L-1, but embryos developed better at 10 to 20 g·L-1. Depending on the genotype, the number of embryos and plants recovered ranged from 3 to 750 and 0.25 to 8, respectively, per 100 flowers. Further increases in the number of embryos (up to 3561 per 100 flowers) and plants (up to 23 per 100 flowers) could be attained by flushing cultures with air enriched with CO2 at 900 μL·L-1. The ploidy level and the microspore origin of the recovered plants were determined by flow cytometry and zymograms for isocitrate dehydrogenase. Nearly 65% of the acclimated plants had undergone spontaneous doubling of the chromosome number, as confirmed by flow cytometry of leaf nuclei. Isocitrate dehydrogenase zymograms demonstrated that plants originated from microspores and that the two parental alleles were equally represented among the haploid and dihaploid plants.

BackgroundMelon (Cucumis melo), an economically important vegetable crop, belongs to the Cucurbitaceae family which includes several other important crops such as watermelon, cucumber, and pumpkin. It has served as a model system for sex determination and vascular biology studies. However, genomic resources currently available for melon are limited.ResultWe constructed eleven full-length enriched and four standard cDNA libraries from fruits, flowers, leaves, roots, cotyledons, and calluses of four different melon genotypes, and generated 71,577 and 22,179 ESTs from full-length enriched and standard cDNA libraries, respectively. These ESTs, together with ~35,000 ESTs available in public domains, were assembled into 24,444 unigenes, which were extensively annotated by comparing their sequences to different protein and functional domain databases, assigning them Gene Ontology (GO) terms, and mapping them onto metabolic pathways. Comparative analysis of melon unigenes and other plant genomes revealed that 75% to 85% of melon unigenes had homologs in other dicot plants, while approximately 70% had homologs in monocot plants. The analysis also identified 6,972 gene families that were conserved across dicot and monocot plants, and 181, 1,192, and 220 gene families specific to fleshy fruit-bearing plants, the Cucurbitaceae family, and melon, respectively. Digital expression analysis identified a total of 175 tissue-specific genes, which provides a valuable gene sequence resource for future genomics and functional studies. Furthermore, we identified 4,068 simple sequence repeats (SSRs) and 3,073 single nucleotide polymorphisms (SNPs) in the melon EST collection. Finally, we obtained a total of 1,382 melon full-length transcripts through the analysis of full-length enriched cDNA clones that were sequenced from both ends. Analysis of these full-length transcripts indicated that sizes of melon 5' and 3' UTRs were similar to those of tomato, but longer than many other dicot plants. Codon usages of melon full-length transcripts were largely similar to those of Arabidopsis coding sequences.ConclusionThe collection of melon ESTs generated from full-length enriched and standard cDNA libraries is expected to play significant roles in annotating the melon genome. The ESTs and associated analysis results will be useful resources for gene discovery, functional analysis, marker-assisted breeding of melon and closely related species, comparative genomic studies and for gaining insights into gene expression patterns.