Solanum incanum 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 : 7

4. Solanum incanum L. , Sp. Pl. 188. 1753.

Solanum sanctum L. , Sp. Pl. ed 2: 269. 1762, nom. illeg. superfl.

Distribution. Ethiopia, Somalia, Arabia, and the Middle East to Pakistan, with some populations in N Kenya, Sudan, and extending to westwards to Mali; thickets, scrubland, and desert savanna; 0–1900 m.

Application of the name S. incanum has been incredibly confused and variable since its first description. This could be grounds for its rejection (see S. linnaeanum below), but we feel its common use to describe eggplant relatives merits its re-circumscription and careful re-use in a more restricted context than previously (e.g., [ 29]). The type specimen of S. incanum chosen by Hepper and Jaeger [ 45] matches material from the Middle East in being densely yellow pubescent with shallowly lobed leaves. Due in part to the misapplication of the name S. incanum to material from India and southeast Asia and confusion over the differences between S. incanum and S. insanum , North African specimens of S. incanum as defined here were often identified and sometimes named as varieties of S. coagulans Forssk. , an unrelated North African species that can easily be distinguished from S. incanum by its fragrant zygomorphic flowers and berry enclosed in an accrescent calyx; see complete synonymy in [ 25]. The most common misapplication of the epithet ‘‘incanum’’ is its use to describe any wild eggplant relative from Africa, most commonly S. campylacanthum .

Solanum incanum ( Fig. 1B ) is a species of dry regions from northern Kenya to Pakistan and in general occurs in drier areas than do other species of the group, although all are weedy and occupy a wide variety of habitats. It is morphologically most similar to S. lichtensteinii of southern Africa and clustered with that species in phenetic analyses [ 29, 30]. The species can be easily distinguished by geography and by the young stems on dry specimens that are more deeply ridged in S. lichtensteinii and only shallowly or not at all ridged in S. incanum .

Lester and Hasan [ 29] proposed that their ‘‘ S. incanum group C’’ (= S. incanum as defined here) was the ancestral type and that all the rest of the species were derived from it in a bidirectional manner (i.e., S. melongena to the east and S. campylacanthum to the south, then giving rise to S. lichtensteinii still further to the south); if polyploidy is indeed occuring in this group (see above under S. campylacanthum ) this scenario needs re-examination. Chromosome counts have not been published for material that is verifiably S. incanum , but high fertility in crosses with S. melongena [ 19] and molecular work with co-dominant SSR markers [ 46] suggests it is diploid. Solanum incanum is being used in eggplant breeding programmes as a source of variation for phenolics content and resistance to drought as well as to develop ILs (introgression lines, see [ 47]; http://zamir.sgn.cornell.edu/Qtl/il_story.htm) as a resource for eggplant breeding [ 46].

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