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Juan José Ruiz and Fernando Nuez

Three clonal hybrids of pepino and their six parental clones were grown in a greenhouse at two salinity levels, 3 and 8 dS·m-1, and two K levels, 246 and 492 mg·L-1. Nearly all the clones maintained high yields even at 8 dS·m-1. Hybrids were highly productive and were more salt-tolerant than their parental clones. In the majority of clones, salinity shortened mean time to harvest by more than 10 days. Salinity also increased organoleptic quality of pepino fruit, mainly due to the increase in soluble solids concentration (SSC). Potassium had little effect on yield and on organoleptic characteristics, although the yield of the less-productive clones appears to be affected by the high level of K (492 mg·L-1). Our results suggest that the pepino could be an alternative crop in areas where only moderately saline water is available, since it is possible to maintain crop productivity while improving its organoleptic quality—the latter being a key issue for its acceptability in European and U.S. markets.

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Jaime Prohens, Juan J. Ruiz, and Fernando Nuez

Parthenocarpy in pepino (Solanum muricatum Aiton) can overcome poor fruit set caused by pollination deficiencies. In two families involving a parthenocarpic parent (Pp), a nonparthenocarpic parent (Pnp), and the generations Pp⊗, Pnp⊗, F1, BCp, BCnp, and F2, we studied three traits that are often confused: parthenocarpy, efficiency of parthenocarpy over seeded fruit set, and the degree of facultative parthenocarpy. Plants were trained to two stems (A and B). On stem A we emasculated six flowers per truss; three were pollinated and the other three were left unpollinated. We considered that a plant was parthenocarpic if it set one or more seedless fruit similar in size and shape to those seeded, and nonparthenocarpic if it only set seeded fruit. The efficiency of parthenocarpy over seeded fruit set was measured with a parthenocarpic fruit set index (PFSI), defined as twice the ratio of seedless to total fruit on stem A. In stem B all flowers were left to self-pollinate naturally. We quantified the degree of facultative parthenocarpy as the percentage of seedless fruit of the total. Parthenocarpy is controlled by one dominant gene for which we propose the symbol P. Parthenocarpic fruit set in the homozygote PP was as efficient as the seeded one (PFSI ≈ 1); in the heterozygote Pp it was less efficient (PFSI ≈ 0.6). The dose of gene P explained the differences found between generations for the PFSI and made it possible to predict the PFSI of a given generation from the proportions of PP and Pp genotypes. Although for the Pp hybrids parthenocarpic fruit set was less efficient than the seeded one, their ability to set seedless fruit in conditions of deficient pollination, together with their high degree of heterosis, makes them agronomically useful. The degree of facultative parthenocarpy seemed to be a complex trait with low heritability. In environments unfavorable for pollination, parthenocarpic genotypes set seedless fruit, thus ensuring crop production and yield stability. Using the degree of facultative parthenocarpy to classify plants for parthenocarpy is not recommended. Developing parthenocarpic cultivars can help spread this crop and stabilize yields.

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Ana Fita, Belén Picó, and Fernando Nuez

Roots are critical for plants to withstand environmental abiotic and biotic stresses. Wild taxa are often used as source of variation for improving root systems, as they are adapted to more stressful soil environments than their cultivated relatives. We studied the genetics of traits related to root biomass, root length, and root architecture (considering the primary/secondary and the tertiary root levels) in melon (Cucumis melo L.) in a 2-year assay by examining the root systems of mature plants in 91 F3 families derived from the cross between a wild accession, Pat 81 [C. melo ssp. agrestis (Naud) Pangalo], and a cultivated accession, `Piel de sapo' (C. melo ssp. melo L.). Despite the difficulties of working with adult plants, we found that Pat 81 and `Piel de sapo' differ greatly in their mature root systems, which is in concordance with the results previously obtained with young roots. Pat 81 developed roots with less biomass than `Piel de sapo', but this wild accession had more favorable root length and architectural traits: a higher density of framework roots, more uniformly distributed along the soil profile, longer laterals with a higher density of branches, and a higher number of root orders. This root structure is linked to a deeper rooting ability and to the capacity of exploiting a larger soil volume. The genetic analysis indicated that length and architectural traits are more stable than biomass traits, both between years and between developmental stages. Moderate to low broad- and narrow-sense heritabilites were found for root length and architectural traits, with most of the observed variation due to additive effects. Our results suggest that Pat 81 could be used as donor of valuable genes for increasing root length and improving the root architecture of cultivated melons, producing melons potentially more tolerant to soil stresses. The lack of phenotypic and genetic correlations between length and architectural parameters and root biomass suggest that root structure can be successfully improved without increasing carbon expenditures.

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Adrián Rodríguez-Burruezo, Jaime Prohens, and Fernando Nuez

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Juan J. Ruiz, Jaime Prohens, and Fernando Nuez

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María Ferriol, Belén Picó, and Fernando Nuez

Cucurbita maxima Duch. is one of the most morphologically variable cultivated species. The Center for Conservation and Breeding of the Agricultural Diversity (COMAV) holds a diverse germplasm collection of the Cucurbita genus, with more than 300 landraces of this species. Morphological and molecular characterization are needed to facilitate farmer and breeder use of this collection. With this aim, the morphological variation of a collection of 120 C. maxima accessions was evaluated. The majority of these accessions originated from Spain, which has acted as a bridge since the 16th century for spreading squash morphotypes between the Americas and Europe. South American landraces (the center of origin of this species) were also included. Eight morphological types were established based on this characterization and previous intraspecific classifications. A subset of these accessions, selected from these classification and passport data, was employed for molecular characterization. Two marker types were used; sequence related amplified polymorphism (SRAP), which preferentially amplifies open reading frames (ORF), and amplified fragment length polymorphism (AFLP). In the main, SRAP marker analysis grouped accessions in accordance to their type of use (agronomic traits) and AFLP marker analysis grouped accessions as to their geographical origin. AFLP marker analysis detected a greater genetic variability among American than among Spanish accessions. This is likely due to a genetic bottleneck that may have occurred during the introduction of squash into Europe. The disparity of the results obtained with the two markers may be related to the different genome coverage which is characteristic of each particular marker type and/or to its efficiency in sampling variation in a population.

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Jaume Prohens, José M. Blanca, and Fernando Nuez

Eggplant (Solanum melongena L.) was introduced by the Arabs into Spain. Since then, many local cultivars have arisen. These materials are grouped in four cultivar groups: “round,” “semi-long,” “long,” and “listada de Gandía.” We studied the morphological and molecular [amplified fragment length polymorphism (AFLP)] diversity of a collection of 28 Spanish traditional cultivars of eggplant. Four eggplant accessions from different origins were used as controls and three scarlet eggplant (Solanum aethiopicum L.) accessions as outgroups. Morphology and AFLP markers showed that S. melongena and S. aethiopicum are separate taxonomic entities, and that, compared to controls, Spanish eggplants are very variable, indicating that the Iberian Peninsula can be regarded as a secondary center of diversity. Morphological differences were found among cultivar groups in traits other than those used for the grouping although, in some cases, accessions from different cultivar groups shared a similar general morphology. Eggplant cultivar groups also showed some genetic differences, which are revealed in the gene diversity statistics (GST = 0.30). Nonetheless, no individual AFLP markers specific and universal to one cultivar group could be found. “Round” cultivars were genetically more diverse than the other cultivar groups. A positive correlation (r = 0.68) was found between morphological and molecular distances. However, correlations between geographical and either morphological or molecular distances were low. Results suggest that evolution of eggplants in Spain has involved frequent hybridizations and a frequent movement and exchange of seeds. Structure of diversity among regions indicates that most of the diversity can be collected in single selected regions. All these results have important implications in eggplant germplasm conservation and breeding.

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Jaime Prohens, Adrián Rodríguez-Burruezo, María Dolores Raigón, and Fernando Nuez

Phenolic compounds have numerous beneficial effects on human health. In consequence, the development of new varieties with higher content of phenolics is of interest for the improvement of the nutritional quality of eggplant (Solanum melongena L.). However, the oxidation of eggplant phenolics causes browning of the cut surfaces of the fruit and reduces its apparent quality. The authors investigated the relationship among, as well as the variation and heritability of, the content of phenolics, ascorbic acid, and soluble solids; pH; and the degree of browning and color difference of the cut surface of the fruit flesh in a collection of 69 eggplant varieties. These included landraces from different origins, commercial varieties, experimental hybrids, and four accessions of the related S. aethiopicum L. and S. macrocarpon L. species. Analyses of variance revealed significant differences among the materials studied for all traits considered. The concentration of phenolics in S. melongena spanned a threefold range, although the highest (1122 mg·kg−1) and lowest (134 mg·kg−1) concentrations of phenolics were found in S. macrocarpon and S. aethiopicum respectively. Concentrations of ascorbic acid were very low, a mean 27 times lower than those of phenolics, and soluble solids content ranged from 3.60% to 6.60% with a pH that ranged from 5.01 to 5.93. Commercial varieties had, as a mean, a 20% lower concentration of phenolics than landraces, as well as a lower degree of browning and color difference. Positive correlations existed between phenolic concentration and degree of browning (r = 0.388) and color difference (0.477), although only 15.1% and 22.8% of the total variation in degree of browning and color difference, respectively, could be attributed to variation in phenolics. Ascorbic acid, soluble solids content, and pH were not correlated to either degree of browning or color difference. The heritability was moderate for phenolic concentration (0.50) and high for degree of browning (0.71) and color difference (0.82). The information obtained indicates that there are opportunities for the development of new varieties with a high concentration of phenolics and low or moderate browning.

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Joaquín Costa, Soledad Catalá, Francisco Botella, Fernando Nuez, and Jesus Cuartero

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Joan Casals, Lluís Bosch, Francesc Casañas, Jaime Cebolla, and Fernando Nuez