Phylogenetic Relationships

Based on morphological characters, phylogenetic relationships, and geographic distribution, 13 species of wild tomatoes, including the cultivated tomato (Solanum lycopersicum), and four closely related species have been recognized as part of the tomato clade. Their distinguishing characteristics, distribution, and habitats, are described in Table 1. Four species have been segregated from the highly polymorphic green-fruited species S. peruvianum sensu lato (sensu lato refers to a broad concept of a species): S. arcanum, S. huaylasense, S. peruvianum, and S. corneliomulleri. The first two have been described as new species (Peralta et al. 2005) from Perú, while the latter two had already been named by Linnaeus (1753) and MacBride (1962), respectively. Another yellow- to orange-fruited species, S. galapagense, was segregated from S. cheesmaniae; both are endemic to the Galápagos Islands (Darwin et al. 2003; Knapp and Darwin 2007). Peralta et al. (2007) are treating these 13 species, in addition to four closely related species (S. juglandifolium, S. lycopersicoides, S. ochranthum, S. sitiens), in the taxonomic series Systematic Botany Monographs.

Resolving evolutionary relationships within the tomato group has been difficult due to the young age of the group, which increases the probability of shared polymorphism among groups, and the low levels of variation within and between the self-compatible taxa. Morphologically, classification has also been made difficult by the unfamiliarity of initial systema-tists with the intraspecific variation (Warnock 1988). A wide variety of studies, using morphological (Peralta and Spooner 2005) and molecular characters such as chloroplast and mitochondrial restriction sites, nuclear RFLPs, isozymes, internal transcribed spacer (ITS), and granule bound starch synthase (GBSSI or waxy) sequences, simple sequence repeats (SSRs), and amplified fragment length polymorphisms (AFLPs) have been carried out to determine the wild tomato phylogeny. Although evolutionary relationships are not completely resolved, consensus has been emerging on several aspects of the group. Some recent results based on sequences of the structural gene GB-SSI (Peralta and Spooner 2001), AFLPs (Spooner et al. 2005), morphology (Peralta and Spooner 2005), and more recently with multiple single-copy genes (Rodriguez et al. 2006) are highlighted below, illustrating our current understanding of phylogenetic relationships within the group (Fig. 1):

1. The tomatoes s.l. (sects. Lycopersicoides, Jug-landifolia and Lycopersicon) are clearly mono-phyletic and sister to the potatoes, with sect. Etuberosum clearly monophyletic and sister to potatoes + tomatoes s.l.

2. Section. Lycopersicoides (formerly recognized as a subsection of sect. Lycopersicon) is clearly monophyletic and sister to sect. Juglandifolia + sect. Lycopersicon.

3. Section. Juglandifolia is clearly monophyletic and sister to sect. Lycopersicon.

4. Within sect. Lycopersicon, S. pennellii in most cases appears at the base of the trees as a poly-tomy with S. habrochaites, or sometimes forms a clade with this species. We consider this relationship unresolved, but the morphological data suggest that S. pennellii is sister to the rest of the tomatoes (sect. Lycopersicon); it is the only species that lacks the sterile anther appendage character shared with the outgroups.

5. Solanum chilense, S. corneliomulleri, S. huay-lasense, S. peruvianum, S. habrochaites and S. pennellii appear as a polytomy at the base of the GB-SSI tree, and the first four clustered with morphological characters, but there is a conflict with the AFLP and morphological data regarding the

Table 1. Species list for tomatoes and wild relatives (with equivalents in the previously recognized genus Lycopersicon, now part of a monophyletic Solarium), along with characteristic fruit color, breeding system, and distribution

Name in Peralta et al. (2007) Lycopersicon equivalent Fruit color

Breeding system1

Distribution and habitats

S. lycopersicoides Dunal

S. sitiens I.M. Johnst. S. juglandifolium Dunal

S. ochranthum Dunal S. pennellii Correll

S. habrochaites S. Knapp and D.M. Spooner

S. huaylasense Peralta

S. peruvianum L.

L. lycopersicoides (Dunal in DC.) A. Child ex J.M.H. Shaw L. sitiens (I.M. Johnst.) J.M.H. Shaw

L. juglandifolium (Dunal) J.M.H. Shaw

L. pennellii (Correll) D'Arcy Green

Green-yellow when maturing, black when ripe

Green-yellow when maturing, brown and dry when ripe Green to yellow-green

Green to yellow-green

L. hirsutum Dunal

S. chilense (Dunal) Reiche L. chilense Dunal

Part of

L. peruvianum (L.) Miller L. peruvianum (L.) Miller

Green with darker green stripes

Green to whitish green with purple stripes

Typically green with dark green stripes

Typically green to greenish-white, sometimes flushed with purple

SI, allogamous

SI, allogamous SI, allogamous

SI, allogamous

Usually SI, some SC in South of species range Typically SI, with SC populations in N and S of species range SI, allogamous

Typically SI, allogamous Typically SI, allogamous

S. corneliomuelleri J.F. Macbr. Part of

Typically green with dark green Typically SI, allogamous

(one geographic race: Misti nr. Arequipa)

L. peruvianum (L.) Miller; or purple stripes, also known as L. glandulosum C.F. Müll.

sometimes flushed with purple

Southern Peru to northern Chile on the western slopes of the Andes on dry rocky hillsides, 1,500-3,700 m

Northern Chile, western Andean slopes on rocky hillsides and dry quebradas, 2,500-3,500 m Northeastern Colombia to southern Ecuador, on the edges of forest clearings, open areas and roadsides, 1,200-3,100 m

Central Colombia to southern Peru, in montane forests and riparian sites, 1,400-3,660 m

Northern Peru to northern Chile, in dry rocky hillsides and sandy areas, from sea level to 2,850 m

Central Ecuador to Central Peru. In premontane forests to dry forests on the western slopes of the Andes, occasionally in lomas formations in northern Peru, 400-3,600 m

Southern Peru to northern Chile. On western slopes of the Andes, hyper-arid rocky plains, dry river beds, and coastal deserts, from sea level to 3,000 m Northern Perú (Department of Ancash). On the rocky slopes along rivers, 1,700-3,000 m Central Peru to northern Chile. In lomas formations and occasionally in coastal deserts from sea level to 600 m, sometimes growing as a weed at field edges in coastal river valleys

Central to southern Perú. On western slopes of the Andes, (400) 1,000-3,000 m, and on lower slopes on the edges of landslides (huaycos) towards the southern range of the species distribution

1 SI Self-incompatible; SC Self-compatible

Table 1. (continued)

Name in Peralta et al. (2007) Lycopersicon equivalent Fruit color

Breeding system1

Distribution and habitats

S. arcanum Peralta (four geographic races: "humifusum", lomas, Maranon, Chotano-Yamaluc) S. chmielewskii (C.M. Rick, Kesicki, Fobes and M. Holle) D.M. Spooner, G.J. Anderson and R.K. Jansen S. neorickii D.M. Spooner, G.J. Anderson and R.K. Jansen

S. pimpinellifolium L.

S. lycopersicum L.

Part ofl. peruvianum (L.) Miller

L. chmielewskii C.M. Rick, Kesicki, Fobes and M. Holle

L. parviflorum C.M. Rick, Kesicki, Fobes and M. Holle

L. pimpinellifolium (L.) Miller

L. esculentum Miller

Typically green with dark green stripes

Typically green with dark green stripes

Typically green with dark green stripes

S. cheesmaniae (L. Riley) Fosberg

S. galapagense S.C.Darwin Part of L. cheesmaniae and Peralta L. Riley

L. cheesmaniae L. Riley Yellow, orange Yellow, orange

Typically SI, allogamous, Northern Peru. Coastal and inland Andean valleys, rare populations SC, on dry rocky slopes, 100 to 2,500 m autogamous, facultative allogamous

SC, facultative allogamous Southern Peru to northern Bolivia (Sorata). In high dry Andean valleys, 2,300-3,000 m

SC, highly autogamous

SC, autogamous, facultative allogamous

SC, autogamous, facultative allogamous

SC, exclusively autogamous SC, exclusively autogamous

Southern Ecuador to southern Perú. In dry Andean valleys, 1,950-3,000 m, often growing over rocky banks and roadsides. Sometimes found in sympatry with S. chmielewskii

Apparently native to coastal areas from Central Ecuador to southern Peru, 0-500 m, parts of Chile2, adventive in N. America. Grows in humid places and on the edges of cultivated fields throughout its native range and has apparently escaped from cultivation in the Galápagos

Apparently native to Perú; the domesticated form of S. lycopersicum now occurs worldwide. The cherry tomato, commonly known as S. lycopersicum var. cerasiforme, has been suggested as the ancestor of cultivated tomato and can often be found growing as a weed in temperate habitats and the edges of cultivated fields, where it is not necessarily native; recent studies suggest S. lycopersicum var. cerasiforme may be a mixture of wild and cultivated tomatoes, rather than an ancestor (Nesbitt and Tanksley 2002) Endemic to the Galápagos Islands (Ecuador) from sea level to 1,300 m

Endemic to the Galápagos Islands, particularly the western and southern islands, mostly occurring on coastal lava and on volcanic slopes, sea-level to 650 m, exceptionally up to 1,500 m in Fernandina and Santiago Islands

: It is uncertain wether the populations are native or adventive in Chile

Fig. 1. Abstracted cladistic results of the 65 accessions ofthe 13 tomato species (in-group sect. Lycopersicon) and ten outgroup taxa (out-groups sect. Juglandifolia, sect. Lycopersicoides, sect. Petota, sect. Etuberosum and sect. Basarthrum) examined in the phylogenetic analysis of the GBSSI gene sequences by Peralta and Spooner (2001). Numbers indicate bootstrap values, and decay values are indicated between parentheses


■ Solanum lycopersicum

■ Solanum pimpinellifolium

■ Solanum cheesmaniae

■ Solanum galapagense

■ Solanum arcanum

■ Solanum chmielewskii

■ Solanum neorickii

■ Solanum huaylasense

■ Solanum peruvianum

■ Solanum corneliomulleri

■ Solanum chilense

■ Solanum habrochaites

■ Solanum pennellii Solanum juglandifolium Solanum ochranthum

■ Solanum lycopersicoides

■ Solanum sitiens

■ Solanum tuberosum

■ Solanum bulbocastanum

■ Solanum jamesii

■ Solanum etuberosum

■ Solanum palustre

■ Solanum muricatum sect. Lycopersicon

|sect. Juglandifolia |sect. Lycopersicoides sect. Petota

|sect. Etuberosum isect. Basarth rum relationships of S. huaylasense (only one accession of S. huaylasense was examined with GBSSI). AFLPs place S. huaylasense with S. arcanum, but with bootstrap values below 50%; morphological phenetics places S. huaylasense with S. chilense.

6. The self-compatible green-fruited species S. chmielewskii and S. neorickii are closely related to S. arcanum, comprising a monophyletic group supported in almost all data sets.

7. The four species with brightly colored fruit (S. cheesmaniae, S. galapagense, S. lycopersi-cum, S. pimpinellifolium) unambiguously form a closely related monophyletic group.

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