Solanum betaceum
Apparently native to southern Bolivia and adjacent northwestern Argentina; cultivated throughout the Andes in subtropical climates, 1000-3000 m in elevation; introduced into Mexico, Central America, and the West Indies; in cultivation in Spain, Portugal, France, the United Kingdom, the Netherlands, Italy, the Canary Islands, Ghana, Ethiopia, Zaire, Uganda, Tanzania, Zimbabwe, South Africa, India, Sri Lanka, Bhutan, Sumatra, Java, New Guinea, New Caledonia, New Zealand, Australia, and the United States.
Solanum betaceum belongs to the Cyphomandra clade of Solanum along with other species traditionally recognized in sections Pachyphylla and Cyphomandropsis (Bohs, in press a). Within the Cyphomandra clade, S. betaceum belongs to a well-supported clade that also includes S. maternum, S. roseum, and S. unilobum (Bohs, in press b). Wild and cultivated accessions of S. betaceum have nearly identical ITS sequences.
Brücher, H. 1968. Die genetischen Reserven Südamerikas für die Kulturpflanzenzuchtung.
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Cabrera, A. 1976. Regiones fitogeograficas Argentinas.
Editorial Acme, Buenos Aires, Argentina.
Brücher, H. 1977. Tropische Nutzpflanzen.
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Bohs, L. 1994. Cyphomandra (Solanaceae).
Flora Neotropica Monograph 63: 1-175. New York Botanical Garden, Bronx, NY.
Bohs, L. 1995. Transfer of Cyphomandra (Solanaceae) and its species to Solanum.
Taxon 44: 583-587.
Bohs, L. & A. Nelson 1997. Solanum maternum, a new Bolivian relative of the tree tomato.
Novon 7: 341-345.
Bohs, L. 2005. Major clades in Solanum based on ndhF sequences.
Pp. 27-49 in R. C. Keating, V. C. Hollowell, & T. B. Croat (eds.), A festschrift for William G. D’Arcy: the legacy of a taxonomist. Monographs in Systematic Botany from the Missouri Botanical Garden, Vol. 104. Missouri Botanical Garden Press, St. Louis.
Bohs, L. 2007. Phylogeny of the Cyphomandra clade of the genus Solanum (Solanaceae) based on ITS sequence data.
Taxon 56: 1012-1026.
chloroplast ndhF sequence: GenBank U47428 (voucher: Bohs 2468, UT). http://www.ncbi.nlm.nih.gov/entrez/viewer.fcgi?db=nucleotide&val=1572915 nuclear ITS sequence: GenBank AY523872 (cult. New Zealand; no voucher). Sequence not yet released (7/04). nuclear ITS sequence: GenBank AY523873 (voucher: Bohs 1599, GH). Sequence not yet released (7/04). nuclear ITS sequence: GenBank AY523874 (voucher: Bohs 2274, GH). Sequence not yet released (7/04). nuclear ITS sequence: GenBank AY523876 (cult. Peru; no voucher). Sequence not yet released (7/04). nuclear ITS sequence: GenBank AY523871 (voucher: Bohs 2837, UT). Sequence not yet released (7/04). nuclear ITS sequence: GenBank AF244713 (voucher: Bohs 2468, UT). http://www.ncbi.nlm.nih.gov/entrez/viewer.fcgi?db=nucleotide&val=7533133 nuclear ITS sequence: GenBank AY523875 (voucher: Bohs 2946, UT).
Solanum betaceum is most closely related to S. maternum; both species have deeply cordate and pubescent leaf blades, pinkish subcoriaceous stellate corollas, cylindrical styles and unexpanded stigmas, and large ellipsoidal juicy fruits that are edible at maturity. Solanum betaceum differs from S. maternum (and the other species in the S. betaceum clade) in its orange or reddish fruits and self-compatible breeding system.
The natural range and place of origin of S. betaceum was unknown until recently. This species is grown worldwide in subtropical areas and herbarium specimens exist from nearly all countries in the Western Hemisphere. Many accounts describe S. betaceum as being known only from cultivation. However, several botanists (Brücher, 1968, 1977; J. Solomon, pers. comm.; E. Zardini, pers. comm.) reported wild populations of S. betaceum from southern Bolivia and adjacent areas of northwestern Argentina in the floristic province known as the “bosque Tucumano-Boliviano” (Cabrera, 1976). Herbarium specimens from these areas show no morphological differences from those of other regions of Latin America and the Old World.
Recent botanical expeditions to southern Bolivia and northwestern Argentina in 1998-2000 confirmed the existence of wild populations of S. betaceum in this region. Wild plants were morphologically indistinguishable from cultivated individuals and wild plants also had a self-compatible breeding system. There is virtually no doubt that these are truly wild individuals, not feral plants established from cultivated tree tomatoes. The plants are common in undisturbed forest and occupy an extensive range from Dept. Tarija, Bolivia to Provs. Salta and Jujuy in Argentina. ITS sequences from wild individuals were identical or nearly so to those of cultivated tree tomatoes from New Zealand and other parts of Latin America.
It is unknown how and when S. betaceum spread from southern Bolivia and northwestern Argentina to northwestern South America where it is most commonly cultivated today. The lack of morphological and molecular divergence between wild and cultivated S. betaceum accessions argues for a relatively recent, possibly post-Conquest, introduction into northwestern South America. Routes of commerce from colonial towns such as Salta and Jujuy in Argentina and Tarija in Bolivia may have extended through Potosí, Bolivia and thence to Lima, Peru and sites father north. Alternatively, the Incas may have spread this fruit crop throughout their empire, which extended in pre-Conquest times from Colombia to Argentina.
Although S. betaceum is widely grown on a local scale in Latin America, New Zealand is the only country to commercially market and export this species. The New Zealanders changed the name to “tamarillo” to avoid confusion with the tomato, S. lycopersicum. They have also instituted breeding and improvement programs for this species using germplasm from variants of S. betaceum as well as other species in the S. betaceum clade. Greenhouse crossing trials among accessions of S. betaceum, S. maternum, S. roseum, and S. unilobum showed that fertile hybrids can be formed in at least some crossing combinations of S. betaceum with the other species (Bohs, 1991; Bohs & Nelson, 1997). Thus, it seems possible to introduce desirable genes into S. betaceum using conventional plant breeding methods. However, there has not been wholesale acceptance of S. betaceum fruits outside New Zealand, and even in New Zealand tamarillo cultivation appears to be on the decline. Nonetheless, additional wild populations of S. betaceum should be located in South America and both in situ and ex situ germplasm preservation of this species should be a priority.