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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.

[ES] Las diferentes técnicas basadas en el cultivo in vitro permiten al mejorador aumentar la eficiencia en los programas de mejora. Una de las técnicas más utilizadas en Prunus es el rescate de embriones inmaduros, que permite germinarlos cuando las semillas procedentes de los cruces en que los dos parentales o el genitor femenino son una variedad precoz con embriones inmaduros que son incapaces de germinar in vivo. La principal dificultad que tiene este método es el bajo porcentaje de germinación de los embriones inferiores a 5 mm de diámetro. El objetivo de este trabajo experimental fue encontrar un medio que aumente el porcentaje de germinación de los embriones inferiores a 5 mm de diámetro añadiendo diferentes combinaciones de tres hormonas (Ácido Giberélico, Bencilaminopurina y Kinetina) en cuatro cruces de distintas variedades mediante la utilización del rescate de embriones en cultivo in vitro. Al final del proceso experimental no se observaron diferencias estadísticamente significativas entre el control y los diferentes tratamientos hormonales efectuados en el éxito del rescate de embriones inferiores a 5 mm de diámetro., [EN] Different techniques based on in vitro culture allow breeders to increase efficiency in their programs. One of the techniques used in Prunus is immature embryo rescue, allowing germinated when seeds from crosses in which the two parental or the female parent is an early variety with immature embryos are unable to germinate in vivo. The main difficulty of this method is the low percentage of germination of the embryos when they have less than 5 mm in diameter. The objective of this experimental work was to find a way to increase the germination percentage of embryos less than 5 mm in diameter by adding different combinations of three hormones (gibberellic acid, benzylaminopurine and kinetin) in four crosses of different varieties, using in vitro embryo rescue. The final results did not show statistical differences between control and hormonal treatments performed in the success of embryo rescue in embryos with less than 5 mm in diameter

A pear rootstock breeding program aiming to enhance tolerance to iron chlorosis is under development. Eighty-six individuals derived from four inter-specific crosses including Pyrus amygdaliformis, P. amygdaliformis ssp. persica, P. elaeagrifolia and P. communis ssp. cordata, were preselected from a field plot based on a comparison to the open pollinated Pyrus communis ‘Williams’ seedlings used as controls. Once established in vitro, they were micropropagated, and the rooted plantlets were tested in vitro for tolerance to iron chlorosis, using six to eight repetitions per clone, before they were acclimated. Twelve plants per clone were transplanted to the field, grafted with ‘Conference’, and their chlorosis level measured during two years. In comparison with previous assays, the availability of repetitions to perform the in vitro test, as well as for the field evaluation, has considerably increased the significance of the regression between in vitro and field response, although the in vitro test was performed on the rootstock and the field response was evaluated on the scion. The level of prediction of the field performance by the in vitro test differed for each cross. The best prediction was found for crosses with P. amygdaliformis (R2=0.72), P. communis var. cordata (R2=0.44), and P. elaeagrifolia (R2=0.41). Further adaption of the in vitro test and studies on the interactions between ‘Conference’ and some rootstocks might improve the lower levels of correlation. According to the in vitro selection tests, the crosses with the highest iron chlorosis tolerance derived from P. amygdaliformis var. persica and P. amygdaliformis, followed by P. communis var. cordata. These are significantly better (p<0.001) that P. elaeagrifolia and P. communis ‘Williams’ seedling. Up to now, the top performing clones derive from P. amygdaliformis, P. communis ssp. cordata, and P. amygdaliformis var. persica. This is in agreement with the tolerance observed in the field.

Background Melon (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. Result We 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 othe

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.