Solanum insanum L.

Ranil, R. H. G., Prohens, J., Aubriot, X., Niran, H. M. L., Plazas, M., Fonseka, R. M., Vilanova, S., Fonseka, H. H., Gramazio, P. & Knapp, S., 2016, Solanum insanum L. (subgenus Leptostemonum Bitter, Solanaceae), the neglected wild progenitor of eggplant (S. melongena L.): a review of taxonomy, characteristics and uses aimed at its enhancement for improved eggplant breeding, Genetic Resources and Crop Evolution 64 (7), pp. 1707-1722 : 1711-1717

publication ID	https://doi.org/ 10.1007/s10722-016-0467-z
DOI	https://doi.org/10.5281/zenodo.6329427
persistent identifier	https://treatment.plazi.org/id/861C87F5-550C-FFB6-FFF5-F9B1C0F867D4
treatment provided by	Diego
scientific name	Solanum insanum L.
status

Treatment

Solanum insanum L. View in CoL , Mant. 1:46, 1767.

Type. India. Gujarat: Surat, Collector unknown (lectotype, designated by Hepper and Jaeger 1985, pg. 389: LINN 248.9 !).

Figures 1 View Fig , 2 View Fig

Erect or prostrate branched shrub, 0.5–1.5 m, prickly. Young stems terete, occasionally purplish, moderately stellate-pubescent to glabrescent with minute simple hairs, prickly, the stellate trichomes porrect, translucent, stalked, thestalks to 0.2 mm long, the rays 6–12, 0.2–0.4 mm long, the midpoints ca. same length as the rays or to 1 mm, the prickles 3–8 mm long, 0.5–5 mm wide at base, straight, flattened, yellow–orange or purple, glabrous, spaced 2–10 mm apart; bark of older stems glabrescent, gray to brown. Sympodial units difoliate, the leaves not geminate. Leaves simple, the blades 2.5–12 cm long, 1.3–8 cm wide, ca. 1.5X longer than wide, ovate, chartaceous, with 2–20 prickles on both surfaces, the prickles green or purple; adaxial and abaxial surfaces moderately stellate-pubescent with porrect, sessile or stalked trichomes, the stalks to 0.2, the rays 5–8, 0.3–1 mm long, the midpoints ca. same length as the rays; major veins 3–5 pairs, sometimes purplish near the petiole, the finer venation usually visible abaxially but not adaxially; base truncate, sometimes obtuse; margins lobed, the lobes 2–3 on each side, 0.5–1.2 cm long, broadly deltate, apically rounded, the sinuses extending 1/4–1/3 of the distance to the midvein; apex rounded to acute; petiole 0.7–3 cm long, 1/4–1/3 of the leaf blade length, 2–3 mmm in diameter, moderately stellate-pubescent to glabrescent, with 0–5 prickles. Inflorescences apparently terminal or lateral, 2.5–3.5 cm long, unbranched, with 1–3 flowers, 1 flower open at any one time; axes moderately stellate-pubescent to glabrescent, unarmed; peduncle 0–13 mm long; pedicels 0.8–1 cm long, erect, articulated at the base, moderately stellatepubescent to glabrescent, unarmed; pedicel scars spaced 1–2 mm apart. Flowers 5(-6)-merous, heterostylous and the plants andromonoecious, with the lowermost flower long-styled and hermaphrodite, the distal flowers short-styled and staminate. Calyx 0.5–1 cm long, moderately stellate–pubescent, with 0–15 prickles, thelobes 4–6 mm long, deltate, apically acute. Corolla 1.6–2.6 cm in diameter, mauve, almost rotate, lobed for ca. 1/4 of the way to the base, the lobes 7–10 mm long, 10–15 mm wide, broadly deltate, spreading, sparsely stellate-pubescent abaxially, thetrichomes porrect, sessileor stalked, thestalks to 0.2 mm, the rays 4–8, 0.2–0.7 mm long, the midpoints ca. same length as the rays. Stamens equal, with the filament tube ca. 1.5 mm long, the free portion of the filaments ca. 1 mm long; anthers 4.5–6 mm long, connivent, tapering, poricidal at the tips. Ovary stellate-pubescent in the upper 1/4; style 0.5–0.7 cm long in long-styled flowers (0.2–0.3 cm long in short-styled flowers), broad and straight, moderately stellate-pubescent in the lower 1/2. Fruit a spherical berry, 1–2 per infructescence, 1.5–3 cm in diameter, the pericarp smooth, dark green with pale green and cream markings when young, yellow at maturity, glabrous; fruiting pedicels 1.5–2.2 cm long, 1.5–3 mm indiameter at base, woody, pendulous, with 0–5 prickles; fruiting calyx lobes expanding to 9–15 mm long, 1/4–1/3 the length of the mature fruit, reflexed, with 2–30 prickles. Seeds ca. 50–150 per berry, 2.4–3 mm long, 1.8–2.2 mm wide, flattenedreniform, orange–brown, the surfaces minutely pitted, thetestal cells with straight lateral walls. Chromosome number: n = 12 ( Meyer et al. 2012).

Distribution

( Figure 3 View Fig ) Solanum insanum occurs throughout south and southeast Asia, from eastern Pakistan extending southwestwards to the Indian Ocean islands of Madagascar and Mauritius (where itmay have been taken by people) and eastwards to the Philippines. Bean (2012 onwards) reports S. insanum as naturalized in Queensland; this is certainly an introduction.

Solanum insanum has been cited as occurring in Afghanistan (https://training.ars-grin.gov/gringlobal/ taxonomydetail.aspx?id=462492), but no specimens or references are cited. We have seen no herbarium specimens of S. insanum from Afghanistan, but the related species S. incanum is known from Iran, Afghanistan and western Pakistan in desert areas.

Habitat and ecology

Solanum insanum is an annual or perennial weed usually growing in open fields and disturbed habitats around villages and other human-impacted areas. In Sri Lanka, we have observed it cultivated in home gardens in all climatic zones as well as in shifting cultivation (slash and burn cultivation) in the drier parts of the island (0–600 m) where it grows on a wide range of geographical, climatic and soil conditions and thrives well even in infertile soils. This suggests that material of S. insanum might be useful for eggplant breeding for adaptation to drought and other abiotic environmental stresses.

Comparison of S. insanum with closely related S. melongena and S. incanum

Solanum insanum is very variable morphologically both across its range and within populations ( Knapp et al. 2013). Hepper (1987) treated S. insanum as a variety of S. melongena in his treatment of Solanaceae in the Flora of Ceylon where he indicated that ‘‘many forms of this variable species are apparent, even in a single wild population’’. In fact, many intermediate forms between S. melongena and S. insanum are present in Southeast Asia, indicating that gene flow exists between both species ( Davidar et al. 2015; Mutegi et al. 2015). Considerable variation has also been described both between and within populations in central and southern India ( Deb 1979; Karihaloo and Rai 1995; Davidar et al. 2015; Mutegi et al. 2015). All members of the eggplant clade are morphologically very similar ( Knapp et al. 2013). Deb (1989) used prominent morphological traits to investigate the species boundaries of S. insanum , S. melongena and S. incanum , and Lester and Hasan (1990) compared S. insanum and S. incanum ; both these authors distinguished the taxa as different, although later authors ( Lester and Hasan 1991; Daunay and Hazra 2012) used a series of informal group names under the species names ‘‘ S. incanum ’’ and ‘‘ S. melongena ’’ to encompass the variation and partial overlap in character states amongst these plants. As shown using molecular tools, S. insanum , S. melongena , and S. incanum are indeed closely related, but distinct ( Meyer et al. 2012, 2015; Knapp et al. 2013; Mutegi et al. 2015; Aubriot et al. 2016).

Solanum insanum is morphologically similar to the mostly African species S. incanum (distributed from northern Africa to Pakistan, see Vorontsova and Knapp 2016), but can be distinguished from it in its sparser pubescence, less robust and usually straighter prickles, larger flowers, and distribution in Asia (see Table 1 View Table 1 ; Vorontsova and Knapp 2016), although poorly prepared specimens from Pakistan can be difficult to identify. Solanum insanum has erect and prostrate forms throughout its range, while S. incanum is always an erect shrublet or shrub. The two species are possibly sympatric in Pakistan (although we have seen no evidence of this), but S. incanum occurs in drier habitats and further to the west than S. insanum . The distribution of S. incanum is from western Pakistan, Afghanistan and Iran across the Middle East and northern Africa. Citations of S. insanum from these areas are almost certainly references to S. incanum (or to the cultivated eggplant itself). Confusion over the distributional limits of these taxa comes in part from the treatment in Flora Iranica (covering western Pakistan, Afghanistan and Iran; Schönbeck-Temesy 1972) where the correct name, S. incanum , was used, but the distribution of the species was said to include what we know recognize as S. insanum . All specimens cited by Schönbeck-Temesy (1972) are S. incanum .

As a cultivated plant, S. melongena shows morphological differences to S. insanum associated with domestication and subsequent evolution with human populations. These include fewer prickles on all plant parts, larger, often fasciated flowers with supernumerary parts, larger fruits, and spongy fruit mesocarp ( Knapp et al. 2013; see also Table 1 View Table 1 ). Some landraces, however, can approach S. insanum in fruit size or stem prickliness. Also, some modern F1 hybrids have been created by seed companies in southeastern Asia that mimic fruits of S. insanum in fruit size, shape and colour, although they generallyhave noprickles on the calyx. Mutegi et al. (2015) reported outcrossing rate among the wild/weedy populations of S. insanum ranged from 5–33%, indicating a variable mixedmating system. In addition Davidar et al. (2015) suggested that the exserted stigmas of S. insanum are likely to promote outcrossing and the most effective pollinators appeared to be bees, potentially increasing the diversity of S. insanum in wild populations. Because S. melongena and S. insanum are interfertile, and intermediate individuals can be observed, Knapp et al. (2013) suggested a set of criteria useful for ascribing these intermediates to an individual species category. Assignment of a species name to an accessionwould bebasedonthenumber of characters shared (see Table 3 in Knapp et al. 2013). Samuels (2013a) disagreed with the distinction of S. insanum and S. melongena , but offered no new evidence beyond that published previously ( Samuels 2012a) using morphological analysis of a limited number of accessions.

The existence of intermediate hybrids between S. insanum and S. melongena is the basis for the wide variety of taxonomic treatments of these taxa in the past, through strict application of the Biological Species Concept ( Mayr 1942). The eggplant clade is relatively young, with a medianminimumage estimate of 3.4 (2.7–4.1) mya ( Särkinen et al. 2013), which suggests considerable gene flow, even amongst wild species, will be recoverable using more in-depth molecular methods. It is clear in both plants and animals that ongoing hybridization between closely related species is common in nature ( Mallet 2005; Rieseberg 2009). Recent phylogenomic studies in both plants (e.g., Blanca et al. 2012; Bock et al. 2013; Causse et al. 2013; Pease et al. 2016; Novikova et al. 2016) and animals (e.g., Fontaine et al. 2015; Martin et al. 2013; Kryvokhyzha 2014), suggest that speciation with substantial gene flow is more common than previously thoughtand that the degree of introgression can be much higher than expected, especially in rapid, recent radiations (e.g., Pease et al. 2016). We can expectthistobe evenmoretrueindomesticatesthat are not geographically separated from their wild progenitors. Despite evidenceof introgression that sometimes may cause difficulties in assigning a species name to individual plants, we considerit importanttorecognize domesticated species such as S. melongena as distinct from their wild progenitors (here S. insanum ) because domesticated plants are experiencing a completely different selection regime in commensal association with human populations than are their wild relatives.

In their discussion on the typification of S. insanum, Hepper and Jaeger (1985) clearly explain that Linnaeus described S. insanum as distinct from his earlier S. melongena by indicating its prickly stems (and calyx) and thus, indicated that he considered S. insanum a new speciesandnotareplacementnamefor S. melongena (as S. sanctum was for S. incanum in the same publication, Linnaeus 1762). Some authors have suggested that S. insanum was a misprint for S. incanum (see Hepper and Jaeger 1985; Samuels 2016); it is unfortunate the two names are so similar but they are not considered confusable (R. Brummitt, pers. comm.).

Cytology

Hybrids between S. insanum and S. melongena are fully fertile ( Swaminathan 1949; Mittal 1950; Bhaduri 1951; Rao 1956; Kashyap et al. 2003), which is not surprising given that both species are diploid (2n = 24 for S. melongena ). The direct cytological assessment of two accessions of S. insanum with contrasting phenotypes was conducted by Rai (1959). He evaluated one accession with big leaves and few thorns, which was diploid and had 12 chromosomes, and another one with small leaves and dense thorns, which had a small ‘fragment’ in addition to normal diploid complement. Kirti and Rao (1982) also reported 12 chromosomes in S. insanum (2n = 24) and studied chromosome associations and frequencies of associated chromosome arms in S. insanum and its hybrid with S. integrifolium Poir. (= S. aethiopicum L., the Scarlet eggplant, an African species cultivated for its leaves and fruits that is not a member of the Eggplant clade s.s.; see Vorontsova et al. 2013).

Economic botany and phytochemistry

Food value and medicinal uses

Eggplant ( S. melongena ) has long been used in a variety of medicinal and culinary preparations across many different Asian ethnolinguistic groups ( Meyer et al. 2014). Because of the close similarity and taxonomic confusions between S. insanum and S. melongena ( Knapp et al. 2013) , it is often difficult to separate the information on medicinal uses and food value of S. insanum from S. melongena in the literature. For example, Jayaweera (1982) has given the medicinal properties of Solanum surattense Burm. f. (= S. virginianum L.), but both his description and botanical illustration are of the local Sri Lankan form of S. insanum . Our observations in local communities in Sri Lanka indicate that people have a clear knowledge of the differences between S. insanum , known as ‘‘ Ela batu ’’, and S. melongena known as ‘‘ Batu ’’. Knapp et al. (2013) reported that in southern China S. insanum is considered distinct from the cultivated S. melongena by local people. Meyer et al. (2014) compared medicinal attributes of S. melongena and S. insanum in China, India and the Philippines. In all three areas the species were clearly distinguished, but had similar medicinal uses.

In Asia, S. insanum is consumed as a vegetable, mainly as a component of curries, but Meyer et al. (2014) found its consumption was always associated with medicinal properties. In some areas, S. insanum use differs markedly from use of S. melongena , further supporting their distinction. Meyer et al. (2014) found that in the Philippines it is recommended to avoid S. insanum consumption when pregnant; however, domesticated eggplants were associated with improved foetal development, and S. melongena root was used to promote uterine stabilization after miscarriage. In Sri Lanka, people recommend consumption of S. insanum fruits (as a curry) when suffering from colds; conversely S. melongena is not recommended for treatment of the common cold. Solanum insanum is important medicinally across Asia ( Brown 1920; Jayaweera 1982; Sivarajan and Balachandran 1994; Elias et al. 2010; Meyer et al. 2014; Hul and Dy Phon 2014, as S. incanum ); some medicinal uses of S. insanum in selected Asian countries are summarized in Table 2 View Table 2 . Further collection and documentation of such information and knowledge from different Asian ethnolinguistic groups will support the advancement of future pharmacological studies related to S. insanum , as well as helping to promote its use for the breeding of eggplants with improved bioactive properties beneficial for human health ( Plazas et al. 2013).

Pharmacognostical and phytochemical properties of S. insanum

The pharmacognostical and phytochemical properties of cultivated eggplants are well known ( Sulaiman and Shree 2012; Wu et al. 2013; Komlaga et al. 2014) but there is much less information from S. insanum . Elias et al. (2010) assessed extracts of root, fruits and leaves of S. insanum (as S. melongena var. insanum ) used in Ayurvedic preparations and showed that the methanolic extract of root contained the highest number of phytoconstituents such as flavonoids, coumarins, alkaloids, tannins, anthroquinines, phenols, resins, glycosides/reducing sugar, proteins and carbohydrates. Bhakyaraj (2010) suggested that the production of solasodine from field grown plants and in vitro raised callus and hairy roots of S. insanum is an efficient way to generate an alternative source of supply of solasodine, a glycoalkaloid used as a precursor in the production of complex steroidal compounds such as contraceptive pills ( Roddick 1986). Sulaiman and Shree (2012) compared the pharmacognostical and phytochemical properties of root of S. insanum with four other Solanum species; S. insanum had the highest total flavonoid content of the species they used.

The fruit metabolites of S. insanum were studied by Wu et al. (2013) as part of the development of a Solanum -specific metabolic database using LC–TOF-MS. They reported 34 metabolites from the phenylpropanoid, flavonoid/anthocyanin, complex alkaloids and shikimate and aromatic acids pathways in S. insanum . Of these, 31 were present in both S. insanum and S. melongena , but three (the flavonoid glucosides kaempferol-3- O -rutinoside-7- O -glucoside, naringenin-7- O -glucoside, and the flavonone eriodictyol) were present in S. insanum but absent from S. melongena . Meyer et al. (2015) also found that S. insanum had higher total levels of phenolic metabolites than did S. melongena , and that for eight of these, including the most abundant phenolic compound 5- O - (E)-caffeoylquinic acid, these differences were significant. Wu et al. (2013) suggested that the differences between S. insanum and S. melongena were related to domestication and subsequent human selection for chemical properties. Some of the compounds present in S. insanum , like 5- O -(E)-caffeoylquinic acid, have bioactive properties of interest for human health ( Plazas et al. 2013). However, further studies on pharmacognostical and phytochemical properties of S. insanum are needed to assess its potential role in the improvement of bioactive constituents of eggplant.