Solanum melongena L.

Knapp, Sandra, Vorontsova, Maria S. & Prohens, Jaime, 2013, Wild Relatives of the Eggplant (Solanum melongena L.: Solanaceae): New Understanding of Species Names in a Complex Group, PLoS ONE 8 (2), pp. 1-12 : 10

8. Solanum melongena L. , Sp. Pl. 186. 1753.

Melongena ovata Mill. , Gard. Dict., ed. 8. Melongena no. 1. 1768.

Melongena tereta Mill. , Gard. Dict., ed. 8. Melongena no. 2. 1768.

Melongena incurva Mill. , Gard. Dict., ed. 8. Melongena no. 3. 1768.

Melongena spinosa Mill. , Gard. Dict., ed. 8. Melongena no. 4. 1768.

Solanum album Lour. , Fl. Cochinch. 129. 1790.

Solanum ovigerum Dunal , Nat. Hist. Solanum 210. 1813.

Distribution. Cultivated worldwide throughout the tropics and subtropics outside and in the temperate zone in the summer or in glasshouses. The greatest diversity of landraces and cultivars is found in Asia (India, China and southeast Asia), with secondary centres in the Middle East and around the Mediterranean.

We recognise as S. melongena only cultivated plants, including both ‘‘primitive’’ (‘‘ S. melongena group G’’) and advanced cultivars (see Table 1 ). The 18 th century botanist and gardener Philip Miller [ 54] recognised the eggplant as its own genus based on its ‘‘one-celled’’ fruit, as he did the tomato based on its ‘‘manycelled’’ fruit, and castigated Linnaeus for sinking both into what he considered the overlarge genus Solanum . He described several ‘‘species’’ of his genus Melongena differentiated by their fruit shape and colour; these are certainly cultivars and would not be named as species today ( Fig. 3 illustrates a sample of the diversity of eggplant fruit shapes and colours). Solanum melongena was probably domesticated multiple times [ 21] from populations of S. insanum and considerable gene flow still occurs between the two species. Solanum insanum is a wild plant, although often growing in disturbed areas including those around villages, while S. melongena , even the most primitive cultivars, is always in close association with people. Using the suite of characters in Table 3 will help with identifying difficult specimens (see above under S. insanum ).

Flowers of S. melongena are often fasciated and have more than the standard 5 parts ( Fig. 1F ), this is caused by meristem mutations increasing the number of floral organs in the whorl [ 55]; the increased number of complicated carpels and the spongy mesocarp may have been what led Miller [ 54] to think the fruit had only a single locule. Domestication trends in S. melongena have involved size, shape and taste [ 56, 57] and the diversity of landraces in the area of origin is very large. Using a combination of historical, morphological and molecular information, Meyer et al. [ 21] suggested that S. melongena had been domesticated at least twice, and that it had been brought from east to west into Europe from India by Arab traders and from China east to Japan. Their analyses suggest that a cluster of landraces they called ‘‘ S. melongena subsp. ovigerum’’ (a combination not validly published according to the Code [ 51]) from Malaysia represented a third domestication event; more population-level sampling and markers may reveal the origins of this pattern. The type of S. ovigerum (the basis for ‘‘ S. melongena subsp. ovigerum’’) is not from Malysia, but instead was a cultivated plant with purple or white ovateoblong (egg-shaped) fruit. Nonetheless, the distinctiness of these southeast Asian genotypes is intriguing and merits further investigation. Hurtado et al. [ 58] used genomic SSRs together with morphological passport data to examine variation in cultivated germplasm of S. melongena landraces and advanced cultivars from China, Spain and Sri Lanka. Different selection pressures appear have been applied in the different regions, leading to typical local trait combinations, and they suggest that germplasm collections should also take care to include extensive samples from centres of cultivated diversity as well as wild species.

The nomenclature and synonymy of S. melongena is complex, and is complicated by the description of many plants grown in European botanic gardens with slightly different fruit morphologies as distinct species, type specimens of these names with only flowering material preserved if at all, and that many of these names were not published correctly according the rules of nomenclature [ 51]. The scientific name for cultivated eggplant has been S. melongena with consistent usage since the late 19 th century, thus little confusion exists over the identities of more derived cultivars. Landraces and cultivars are better named using the International Code of Nomenclature for Cultivated Plants [ 59] than by giving them botanical species and infraspecies names.

Figures

Figure 1. Representative flower and fruit morphology of eggplant and its wild relatives. A. Solanum campylacanthum inflorescences (Kenya - Vorontsova et al. 157); B. Solanum incanum immature fruit (Kenya – Vorontsova et al. 203); C. Solanum insanum fruit cross-section (China – Wang et al. 2047); D. Solanum insanum inflorescence with several hermaphrodite flowers (China – Wang et al. 2039); E. Solanum linnaeanum with yellow mature and mottled green immature fruit, note highly dissected leaves (Spain - Knapp IM-10096); F. Solanum melongena flower with duplicated parts (China – Wang et al. 2042). Photographs: A, B taken M.S. Vorontsova; C, D, E, F taken by S. Knapp. doi:10.1371/journal.pone.0057039.g001

Figure 3. Fruit shape and colour variation in cultivars of the common eggplant, Solanum melongena. Photograph taken by J. Prohens. doi:10.1371/journal.pone.0057039.g003