Chlorogenic acid (5-O-caffeoyl-quinic acid; CGA) is an ester of caffeic acid and (-)-quinic acid with many beneficial properties for human health, such as anti-oxidant, anti-inflammatory, cardioprotective, anti-carcinogenic, anti-obesity, and anti-diabetic properties. This has raised an interest for the development of new crop cultivars with increased CGA content. One of the crops with higher CGA content is eggplant (Solanum melongena). There is a wide diversity for CGA content in cultivated eggplant germplasm, which is influenced by the fruit developmental stage, storage conditions, and environmental factors. Therefore, appropriate experimental designs are required for an efficient breeding. Several strategies are proposed for breeding for high CGA content such as intraspecific variation, selection among accessions, development of hybrids and lines with good agronomic and commercial characteristics, or introgression of the high CGA trait in élite lines. Some wild relatives, like S. incanum, present higher CGA contents than those of eggplant. Interspecific hybridization can be used to introgress favorable alleles from the wild species into the genetic background of cultivated eggplant. Fruit flesh browning, as a result of CGA oxidation by polyphenol oxidases, could be a side effect of increasing the CGA content in eggplant. However, experimental results indicate that the relationship between CGA content and fruit flesh browning is low or moderate. Furthermore, selection for low polyphenol oxidase activity might result in reduced fruit flesh browning. Overall, the available data suggest that the development of eggplant cultivars with improved functional quality resulting from a higher CGA content is feasible.

Wild relatives represent a source of variation for many traits of interest for eggplant ( Solanum melongena ) breeding, as well as for broadening the genetic base of this crop. However, interspecific hybridization with wild relatives has been barely used in eggplant breeding programs. As initiation of an introgression breeding program we performed 1424 interspecific hybridizations between six accessions of eggplant from the Occidental and Oriental groups and 19 accessions of 12 wild species from the primary ( Solanum incanum and Solanum insanum ), secondary ( Solanum anguivi , Solanum dasyphyllum , Solanum lichtensteinii , Solanum linnaeanum , Solanum pyracanthos , Solanum tomentosum , and Solanum violaceum ), and tertiary ( Solanum elaeagnifolium , Solanum sisymbriifolium , and Solanum torvum ) genepools. Fruit set, hybrid seed, and seed germination were obtained between Solanum melongena and all wild species of the primary and secondary genepools. The highest fruit set percentage and quantity of seeds per fruit were obtained with the two primary genepool species S. incanum and S. insanum as well as with some secondary genepool species, like S. anguivi , S. dasyphyllum , or S. lichtensteinii , although some differences among species were observed depending on the direction of the hybridization. For small-fruited wild species, the number of seeds per fruit was lower when using them as maternal parent. Regarding tertiary genepool species, fruit set was obtained only in interspecific hybridizations of eggplant with S. sisymbriifolium and S. torvum , although the fruit of the former were parthenocarpic. However, it was possible to rescue viable interspecific hybrids with S. torvum . In total we obtained 58 interspecific hybrid combinations (excluding reciprocals) between eggplant and wild relatives. Some differences were observed among S. melongena accessions in the degree of success of interspecific hybridization, so that the number of hybrid combinations obtained for each accession ranged between 7 (MEL2) and 16 (MEL1). Hybridity of putative interspecific hybrid plantlets was confirmed with a morphological trait (leaf prickliness) and 12 single nucleotide polymorphism markers. The results show that eggplant is amenable to interspecific hybridization with a large number of wild species, including tertiary genepool materials. These hybrid materials are the starting point for introgression breeding in eggplant and in some cases might also be useful as rootstocks for eggplant grafting.

Vegetables represent a major source of phenolic acids, powerful antioxidants characterized by an organic carboxylic acid function and which present multiple properties beneficial for human health. In consequence, developing new varieties with enhanced content in phenolic acids is an increasingly important breeding objective. Major phenolic acids present in vegetables are derivatives of cinnamic acid and to a lesser extent of benzoic acid. A large diversity in phenolic acids content has been found among cultivars and wild relatives of many vegetable crops. Identification of sources of variation for phenolic acids content can be accomplished by screening germplasm collections, but also through morphological characteristics and origin, as well as by evaluating mutations in key genes. Gene action estimates together with relatively high values for heritability indicate that selection for enhanced phenolic acids content will be efficient. Modern genomics and biotechnological strategies, such as QTL detection, candidate genes approaches and genetic transformation, are powerful tools for identification of genomic regions and genes with a key role in accumulation of phenolic acids in vegetables. However, genetically increasing the content in phenolic acids may also affect other traits important for the success of a variety. We anticipate that the combination of conventional and modern strategies will facilitate the development of a new generation of vegetable varieties with enhanced content in phenolic acids.

Eggplant is a powerful source of polyphenols which seems to play a key role in the prevention of several human diseases, such as cancer and diabetes. Chlorogenic acid is the polyphenol most present in eggplant, comprising between the 70% and 90% of the total polyphenol content. Introduction of the high chlorogenic acid content of wild relatives, such as S. incanum, into eggplant varieties will be of great interest. A potential side effect of the increased level polyphenols could be a decrease on apparent quality due to browning caused by the polyphenol oxidase enzymes mediated oxidation of polyphenols. We report the development of a new interspecific S. melongena × S. incanum linkage map based on a first backcross generation (BC1) towards the cultivated S. melongena as a tool for introgressing S. incanum alleles involved in the biosynthesis of chlorogenic acid in the genetic background of S. melongena. The interspecific genetic linkage map of eggplant developed in this work anchor the most informative previously published genetic maps of eggplant using common markers. The 91 BC1 plants of the mapping population were genotyped with 42 COSII, 99 SSRs, 88 AFLPs, 9 CAPS, 4 SNPs and one morphological polymorphic markers. Segregation marker data resulted in a map encompassing 1085 cM distributed in 12 linkage groups. Based on the syntheny with tomato, the candidate genes involved in the core chlorogenic acid synthesis pathway in eggplant (PAL, C4H, 4CL, HCT, C3′H, HQT) as well as five polyphenol oxidase (PPO1, PPO2, PPO3, PPO4, PPO5) were mapped. Except for 4CL and HCT chlorogenic acid genes were not linked. On the contrary, all PPO genes clustered together. Candidate genes important in domestication such as fruit shape (OVATE, SISUN1) and prickliness were also located. The achievements in location of candidate genes will allow the search of favorable alleles employing marker-assisted selection in order to develop new varieties with higher chlorogenic content alongside a lower polyphenol oxidase activity. This will result into an enhanced product showing a lower fruit flesh browning with improved human health properties.