Keywords

1.1 Introduction

Solanaceae is a cosmopolitan family with mostly worldwide distribution on all continents except Antarctica. The greatest concentration of diversity is in Central and South America and it is believed that the family originated there (Hunziker 1979). A recent study by Palchetti et al. (2020) reported that Solanaceae comprises 1611 species in South America. Peru shows the greatest diversity, including genera, total species, and endemic species; in this country, Solanum, Jaltomata and Nolana are the most species-rich genera. Peru also holds the most significant number of potato and tomato species in the world (Peralta et al. 2008; Spooner et al. 2016). Members of the Solanaceae can be found growing in a wide variety of habitats, from deserts to tropical rainforests, from costs to mountain areas (Knapp 2020).

Among angiosperm families, the Solanaceae ranks one of the most important to human beings, containing a number of economically important crops (Table 1.1). Many of them belong to the genus Solanum, which includes Solanum lycopersicum L. (=Lycopersicon esculentum Miller) (tomato), Solanum tuberosum L. (potato), Solanum melongena L. (eggplant or aubergine). Several other species take on great importance such as those belonging to the genus Nicotiana (N. tabacum L.), Capsicum annuum L. (both chili peppers and bell peppers), Physalis spp.(tomatillo, Cape gooseberry, and Chinese lantern), and Lycium (L. barbarum L. and L. chinense L.).

Table 1.1 Worldwide production of the main Solanaceae crop species (Fao 2018)
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Many genera of Solanaceae provide ornamental plants widely used in gardens, including Brunfelsia (Lady of the night), Cestrum (Jessamine), the closely related Brugmansia and Datura (Angel’s trumpet) and Petunia.

1.2 Morphological Characteristics

The Solanaceae family shows a great range of habitus; it generally comprises herbs and shrubs, but also trees, woody vines, lianas, and sometimes epiphytic plants (Fig. 1.1).

Fig. 1.1
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Some Solanaceae habitus: a herbaceous (Petunia × hybrida hort. ex Vilm.); b shrubby (Solanum pseudocapsicum L. ‘Variegatum’); c arborescent (small tree) (Brugmansia arborea (L.) Steud.); d woody climbing (Solanum laxum Spreng.)

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They can be annuals, biennials, or perennials; subterranean tubers are sometimes present. This family does not have either laticifers or latex and prickles, and stellate trichomes can be present in some species.

Leaves present a suite of characteristics useful for plant identification. They are entire to deeply lobed, never compound, with pinnate or reticulate venation, exstipulate, generally simple to pinnatifid or ternate, alternately arranged or opposite (Fig. 1.2). In some species (Physalis), leaves can be alternate at the base of the plant and opposed towards the apex. Petiole is generally present, although leaves can be also subsessile or rarely sessile. This family does not have laticifers nor latex.

Fig. 1.2
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Solanaceae leaf-shapes: entire a Capsicum annuum L.; lobed b Solanum melongena L.; deeply lobed c Solanum lycopersicum L.; lobed and spiny d Solanum mammosum L.

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Flowers are solitary or bore in cymose, racemose, paniculate or compound-corymbose inflorescences, terminal, lateral or axillary. Pollination is generally entomophilous, but some species can be bat-dependent (Sazima et al. 2003). Flowers themselves are dichlamydeous, having both a calyx and a corolla, bisexual or rarely unisexual (e.g., Symonanthus, some Solanum species). The calyx is typically gamosepalous, from tubular to campanulate, with 5 (3–9) lobes, persistent or sometimes accrescent. In a few species (e.g., P. alkekengi L.), sepals resume growth after pollination to encapsulate the mature fruit, forming the “Chinese lantern,” a trait also termed inflated-calyx syndrome (ICS) (Hu and Saedler 2007; Wilf et al. 2017).

Fig. 1.3
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Actinomorphic corollas. Trumpet-shaped: a Lycianthes rantonnetii (Carrière) Bitter; Rotate: b Solanum eleagnifolium Cav.; Tubulose: c Iochroma cyaneum (Lindl.) G.H.M. Lawr. & J.M. Tucker; Funnel-shaped: d Datura stramonium L.; Campanulate: e Solandra maxima (Sessé & Moc.) P.S. Green; Urn-shaped: f Atropa belladonna L.

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The corolla is ebracteate, gamopetalous, actinomorphic (Figs. 1.3 and 1.4) or slightly zygomorphic (Fig. 1.5), rotate, campanulate, tubular, funnel-shaped, trumpet-shaped, or urn-shaped; corolla lobes are generally 5 (varying from 3 to 9), and usually display valvate or plicate arrangement within the flower bud.

Fig. 1.4
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Datura metel L. ‘Ballerina Purple’ is a cultivar with a double corolla, resembling a dancer's costume

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Fig. 1.5
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Slightly zygomorphic corollas: a Nicotiana tabacum L.; b Hyoscyamus albus L.; c Nicandra physalodes (L.) Gaertn

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Stamens are free, usually 5 or 4 (rarely 2, 6, 8), epipetalous and alternate with lobes, equal or unequal in length; anthers are either bilocular or unilocular, dorsifixed, or basifixed, often connivant, longitudinal, or poricidal in dehiscence. Staminodes (stamens with non-bearing anthers) occur in some species (e.g., Schizanthus, Salpiglossis). Gynoecium is syncarpous, with 2 oblique carpels (sometimes 4–5), whereas the ovary is superior and two-loculated; it may be secondarily divided by false septa (e.g., Datura). Style is simple, and stigma is capitate or rarely bilobate. Ovules are numerous, anatropous, and placentation is axile, rarely basal. In this family, fruit is predominantly a berry, a drupe, a capsule (septicidal or rarely loculicidal) (Fig. 1.6). In each fruit, seeds are numerous and hold curved, spiral, or straight embryos; cotyledons are two.

Fig. 1.6
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Berries types in the Solanaceae family: a Solanum lycopersicum L.; b S. melongena L.; c S. chenopodioides Lam.; d S. tuberosum L.; e S. mammosum L.; f Caspicum annuum L.

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1.3 Taxonomy and Domestication

Assigned to Solanales order in the APG IV classification (Stevens 2015), along with Convolvulaceae, Hydroleaceae, Montiniaceae, and Sphenocleaceae, Solanaceae are considered a monophyletic group based on chloroplast DNA restriction (Olmstead and Palmer 1992). It is the largest plant family after Poaceae and Fabaceae and, as typical of large plant families, its classification is difficult and shows several challenges. Traditional classifications of the family typically recognized two subfamilies, Cestroideae and Solanoideae, the former characterized by curved embryos, discoid seeds, and berry-like fruits, the latter with straight embryos, contained in small, angular to subglobose seeds and capsular fruits (Olmstead et al. 2008, D’Arcy 1991). Molecular phylogeny based on two chloroplast DNA regions (ndhF and trnLF) allowed the identification of four main clades at the subfamily level, 14 main clades at the tribe level, around 100 genera, and 2500 species (Olmstead et al. 2008). Recent APG classification (2016) identifies nine clades at subfamily level and 14 at tribe level (Table 1.2).

Table 1.2 Recent classifications of the Solanaceae family
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Solanaceae family began to diversify 50 to 65 million years ago (Magallòn et al. 2013). A Bayesian study by Dupin et al. (2017) on the historical biogeography of Solanaceae pointed out that South America is both the family distributional center as well as its ancestral range, and that dispersal events were the principal mode by which members of the family have spread. The authors hypothesized that short-range movements account for most of the spread beyond South America, although multiple long-distance dispersals to Africa, Australia, and Eurasia occurred.

The tomato was introduced from the Andean region to Europe by the Spanish in the early sixteenth century. Today, it represents the most economically important vegetable crop worldwide (Bergougnoux 2014) (see also Chap. 3). While the Spanish and Italians seem to have been the first Europeans to adopt it as a food, it was initially grown as an ornamental plant in France and Northern Europe because botanists recognized it as a relative of the poisonous belladonna and deadly nightshade (Petruzello 2020a, b).

The cultivated potato traces its origin to Andean and Chilean landraces developed by pre-Columbian cultivators (Spooner et al. 2005) (see also Chap. 4). Remains of cultivated potatoes, identified based on their distinctive starch grains, have been found at coastal sites in Peru dating from 2000 B.C. (Prance and Nesbitt 2012). It would seem likely that potatoes were not seen by Europeans before 1532 when Pizarro first ascended the Andes of northern Peru and was mentioned for the first time in what is now Colombia in 1537, and in Perù by Lopez de Gomara’s in 1552 and Cieza de Leon in 1553 (Hawkes and Francisco-Ortega 1993). The earliest known records of potato cultivation in Europe date at the slightly earlier date of about 1562 in the Canary Islands and from between 1573 and 1576 in Seville in Spain (Hawkes and Francisco-Ortega 1993; Prance and Nesbitt 2012).

Eggplant was domesticated from a group of spiny Solanum species in the Indo-Burma region and was early adopted in China as a vegetable crop (discussed also in Chap. 6). Eggplant was unknown by the ancient Greeks and Romans but spread throughout the Mediterranean Basin due to Muslim expansion in the early Middle Ages (Daunay and Janick 2007; Yılmaz et al. 2013) and nowadays is widely grown in the Americas, Europe, and Asia. Its close relatives: S. aethiopicum L. (scarlet eggplant) and S. macrocarpon L. (African eggplant) are of African origin (Sękara et al. 2007).

The genus Capsicum (chilies and other peppers) comprises annual or perennial herbs and shrubs native to South and Central America. Chilies are believed as one of the earliest domesticated plants in the New World. The oldest evidence of domestication of these plants dates to 5000–6500 B.C. (Davenport 1970) (also reported in Chap. 6). The chili was brought to Europe by Colombus, and enthusiastically and rapidly was incorporated into many cultures. Within 50 years, this spice spread from Spain to England (Lippert et al. 1966). The genus Capsicum consists of 20–27 species (Walsh and Hoot 2001), five of which are widely cultivated (C. annuum L., C. baccatum L., C. frutescens L., C. chinense Jacq. and C. pubescens Ruiz & Pav.) (Heiser and Pickersgill 1969). C. annuum is the most common and extensively cultivated.

The tomatillo (Physalis philadelphica Lam.) is native to Mexico and is thought to have been first domesticated by the Aztecs around 800 BCE and was an important food crop to a number of pre-Columbian peoples in Mesoamerica, including the Mayans (Small 2011; Petruzzello 2020a, b).

Nicotiana tabacum and Nicotiana rustica are native plants of the Americas, having evolved in the Andes around Peru/Ecuador. Tobacco is thought to have been cultivated since about 5000–3000 BC, dispersed by Amerindias through both the southern and the northern American continent. Everywhere in the New World tobacco was employed in sacred magical and medicinal contexts and was undoubtedly more widely used for these purposes than any other plant (Schultes 1979). Tobacco was widely used by native people by the time that Columbus arrived in North America in 1492 (Musk and De Klerk 2003; Goodman 2005). It is likely that the first Europeans to smoke were Columbus’ crew returning from the Americas in the late 15th and early sixteenth centuries (Musk and De Klerk 2003). During the sixteenth century, tobacco use spread throughout all of Europe (Davey 1999).

Recently the dried fruits of L. barbarum L. and L. chinense Mill., have become popular in Europe, where they are known as goji berries, and are considered functional food on account of their high vitamin and mineral content (Samuels 2015). Both species are native to Asia, and most commercial cultivation occurs in Northern China (Wang 2007).

1.4 Importance of Solanaceae Wild Species

In addition to species that underwent domestication, this family encompasses several wild species used in traditional cuisine, as a source of phytochemicals and as font of useful genes/alleles for breeding efforts.

Besides the well-known cultivated species, many wild species are used in the folk cuisine of some rural communities. They are utilized principally as leafy or fruit vegetables thanks to the richness of bioactive compounds contained in their edible parts. Cooked and consumed like spinach are, for example, the young leaves of Jaltomata repandidentata (Dunal) Hunz., (Samuels 2015), while Cestrum nocturnum L. leaves are eaten cooked with tortillas (Kermath et al. 2014). Eaten in the Americas, are the fruits of Acnistus arborescens (L.) Schltdl., Chamaesarcha coronopus (Dunal) A.Gray, Jaltomata spp. (Kermath et al. 2014), Solanum stramonifolium Jacq., S. sessiliflorum Dunal (Turner et al. 2011), Lycianthes asarifolia (Kunth and Bouché) Bitter and L. lycioides (L.) Hassl (Samuels 2015).

Solanaceae are also known for possessing a diverse range of biologically active compounds that may be used both for the benefit of human health and for crop protection. Based on their chemical structure, these metabolites can be classified into three main groups: terpenes (composed almost entirely of carbon and hydrogen and including plant volatiles, cardiac glycosides, carotenoids, and sterols), phenolics (possessing one or more phenol rings and comprising phenolic acids, coumarins, flavonoids, tannins, and lignin), and nitrogen-containing compounds (including alkaloids and glucosinolates) (Chowański et al. 2016). Of all the various classes of compounds, by far alkaloids have received the most attention due to their abundance and properties. They comprise nicotine and tropane alkaloids, and are localized in all plant parts, with the highest concentrations in roots and seeds in proportions that vary among species, time of year, location, and plant organs (Maga 1994). Tropane alkaloids constitute one of the distinctive groups of secondary metabolites of the Solanaceae and, despite their extreme toxicity, are important drugs when administered in appropriate dosages (Shah et al. 2013). Atropine is an anticholinergic drug occurring naturally in a number of species (e.g., Atropa belladonna, Datura stramonium L.) and is classified as muscarinic receptor antagonist (Brown and Taylor 2001). This alkaloid can affect the central as well as the peripheral nervous systems and, in overdoses, is poisonous. Atropine is used in the clinical practice in the management of myopia, as an antidote in Organophosphate poisoning and the treatment of bradycardia (Al 2014; Almubayedh et al. 2018). Hyoscyamine and scopolamine are secondary metabolites of some plants, particularly henbane (Hyoscyamus niger, H. albus). Both these tropane alkaloids are anticholinergics and, when used in small doses, they have medical uses such as treating gastrointestinal disorders (Kumar and Tewari 2018).

Wild Solanaceae are also important for crop improvement. They represent a precious reservoir of genes and alleles lacking in the cultivated species that can be moved into the cultivated gene pools through specific breeding approaches and technologies. Many cultivated varieties of the Solanaceae family have been developed through the exploitation of wild germplasm. A well-known and nice example of this is the contribution of Mexican species Solanum demissum to broaden the resistance to light blight in the common potato, S. tuberosum. Dominant R genes from S. demissum are currently present in most potato varieties, although new pathogen strains have now overcome many of these resistances. Finally, the contribution of wild species from the Solanaceae family is also crucial in genetic and genomic plant research. This part, as well as that related to the use of wild species in breeding, will be better expanded in the next chapters.