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An efficient process of adventitious regeneration from haploid plant leaves to increase the proportion of diploid plants of six elite melon lines ‘Védrantais’ French cultivar, ‘Piel de Sapo’ Spanish line ‘T111’, and four near isogenic lines (NILs: SC 6–6, SC 7–2, SC 7–4, SC 8–4) has been developed. Several hormone combinations, in vitro culture conditions, and leaf positions on the plant stem were analyzed to improve the regeneration frequency and the percentage of diploid plants in these lines. Flow cytometry showed that diploid plant production was optimized by regeneration from haploid leaves as the percentage of diploid plants increased from 11% with regeneration of diploid cotyledons to 60% in this work. Evaluating the four NILs, only the lines SC 6–6 and SC 8–4 showed a significantly higher percentage of diploidy with 80% and 72.7%, respectively. The leaf position factor had no effect on regeneration and ploidy level, while darkness negatively influenced regeneration but had no effect on ploidy. Furthermore, it was concluded that the hormonal combination (cytokinin plus auxin) induces low endoreduplication activity, which is the phenomenon responsible for the polyploidy. Furthermore, this study provided evidence that in melon polyploidy occurs during the process of organogenesis, and, therefore, one should focus on this phase to avoid polyploidization of cells and, thus, avoid polyploid plants.

Según datos de 2019, las especies de fruta dulce y de frutos secos ocupaban en España 194.414 ha y 763.717 ha, respectivamente, con una superifcie total de 958.131 hectáreas.

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 F2 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.