Dr. Charles Rick and colleagues admiring plants along roadside during a collecting expedition.
[photo: TGRC]

The Lycopersicon esculentum Complex

those species which are easily crossed with Lycopersicon esculentum

L. esculentum
L. esculentum var. cerasiforme
L. esculentum var. grandifolium
L. esculentum var. pyriforme
L. esculentum var. validium
L. pimpinellifolium
L. cheesmanii
L. cheesmanii f. minor
L. parviflorum
L. chmielewskii
L. hirsutum f. typicum
L. hirsutum f. glabratum
L. pennellii

L. esculentum

Almost all tomatoes known to those reading this fall within this species. Though variation exists among most of the common tomatoes, they are not seperated into unique botanical varieties due to their common origin. Fresh-market and processing types of tomatoes are in this catagory. Both types originated from the only wild type of tomato found outside of South America, the cherry tomato, L. esculentum var. cerasiforme. Although all forms of L. esculentum are self-compatible and exclusively inbreeders, the wild cherry types tend to outcross. This is due to the stigma of the wild cherry tomatoes which typically exerts beyond the anther cone at anthesis. This allows for a small degree of outbreeding. This may also happen to some degree in other L. esculentum if certain conditions are present (floral morphology, temperature, nutrition).

The domestication of the wild cherry types (L. esculentum var. cerasiforme) in Mexico eventually spread to Europe and by selection led to larger fruited varieties. It is believed that this selection also led to the progressive withdrawal of the stigma into the anther cone (probably by chance). This gave rise to the large-fruited self-compatible inbreeders most of us grow in our gardens today. For this reason it is relatively easy for one to maintain a "true-to-type-variety" (as long as the variety is not a F1 hybrid) by saving their own seed and not have to worry too much about outcrossing with other varieties of tomato.

Most, but certainly not all, L. esculentum are red fruited. Fruit color, shape and quality vary considerably as does growth habit and leaf morphology.

There are several other botanical varieties of tomato. These varieties can be easily intercrossed with each other to produce viable offspring. They are:

L.esculentum var. esculentum
L.esculentum var. cerasiforme cherry tomato
L.esculentum var. pyriforme pear tomato
L.esculentum var. grandifolium potato-leaved tomato
L.esculentum var. validium compact habit
If you'd like to find out about the pedigrees (parental lines) of certain selected lines check out:
Interim Report of the Committee on Varietal Pedigrees 1995-60
Interim Report of the Committee on Varietal Pedigrees 1984

L. pimpinellifolium

This species of Lycopersicon is indigenous to the lower-elevation coastal valleys of Peru (<1,000m). The fruit are small, approximately 1cm in diameter, and red in color (yellow varieties do exist). The fruit size gives it the common name of the 'currant tomato'. The foliage tends to produce a unique odor when crushed. Stems are often smooth and lack the hairs found on L. esculentum. It has been my observation that the stems are not as brittle either. All populations of this species are self-compatible. Some populations of this species differ considerably in morphology while others are highly uniform. Some populations are exclusively autogamous (self-pollinating) while others allow some outbreeding. This is due to exerted stigmas which project well beyond the anther cone (see picture below).

This species tends to readily cross with L. escuentum and is the only one to have exhibited a natural introgression with L. esculentum . In fact it is probable that both species evolved from a common ancestor.

There are thousands of PI's (Plant Introductions) of L. pimpinellifolium. Many of which have been incorporated into L. esculentum to provide useful resistance to several diseases.

Fruit storage life in Lycopersicon pimpinellifolium. (Lobo, M., Alvaran, I. and Cardona, M.P.)
An anomalous accession of L. pimpinellifolium from the Galapagos Islands. (Rick, C. M.)

Fruit, foliage and flowers [photo: Rick, Charles M.]

Flowers showing exherted stigmas [photo H. Teppner]

Fruits on long trusses [photo H. Teppner]
photos courtesy of the Tomato Genetics Resource Center

L. cheesmanii

"L. cheesmanii f. minor

This species is found exclusively in the Galapagos Islands. A subspecies exists , L.cheesmanii subspp. minor, which is generally found in the drier regions of the islands while L.cheesmanii is found closer to the coastal areas. The fruits are red to orange. All forms of L.cheesmanii are self-compatible and exclusively inbreeders. Both forms can be hybridized with the common tomato.

L.cheesmanii has provided several benifits to the common tomato. The first is the incorporation of a single recessive gene that codes for jointless pedicels. This is oftened used as a genetic marker. L.cheesmanii also can be used for its high vitamin C, pro vitamin A and higher soluble solids contents. The subspecies, L.cheesmanii subspp. minor, has the potential for salt and drought tolerance.

Potential of Lycopersicon cheesmanii accessions for improving provitamin A content in tomato. (Stommel, J.R.)
Transfer of 'High Solids' genes from Lycopersicon cheesmanii and L. chmielewskii to tomato. (Poysa, V.)
The use of Lycopersicon cheesmanii in breeding for salt-tolerant tomatoes. (Costa, J., Nuez, F., Anastasio, G. and Palomares, G.)
L.cheesmanii fruit
Fruit of L. cheesmanii (LA0166) [photo H. Teppner]

foliage and fruit
Fruit and foliage
photos courtesy of the Tomato Genetics Resource Center
[photos: Rick, Charles M.]

L. parviflorum

This species is native to regions of Peru. It favors areas around streams. It is self-compatible and, due to floral morphology, is highly autogamous (self-pollinating). L. parviflorum has an extremely small flower and the stigmas rarely protrude out of the anther cone. As a result populations tend to be highly homozygous (genetically similar). Fruits are small (<1cm) and green. L. parviflorum hybridizes easily with L.esculentum and have potential for high soluble solids and vitamin C content.

Fruit, foliage and flowers
photo courtesy of the Tomato Genetics Resource Center
[photo: Rick, Charles M.]

L. chmielewskii

This species is also native to Peru. It too prefers moist areas like L. parviflorum but prefers the soil to be well drianed. Fruit are green and >1cm in diameter. It is self-compatible but is oppposite in floral morphology to L. parviflorum. The flowers are large and very showy with long exerted stigmas. This seems to encourage outbreeding and, as a result, much heterozygosity (genetic differences) is present in populations of L. chmielewskii. This species also has the potential for high soluble solids and vitamin C content.

Sucrose accumulator (sucr), a gene controlling sugar composition in fruit of L. chmielewskii and L. hirsutum. (Chetelat, R.T., et.al.)

L. chmielewskii plants in native habitat
photo courtesy of the Tomato Genetics Resource Center
[photo: Rick, Charles M.]

L. hirsutum

L. hirsutum f. glabratum

This species is native to Peru and southern parts of Ecuador and has very small, green, hairy fruit. The species is divided into to seperate subspecies, L. hirsutum f. typicum and L. hirsutum f. glabratum.

L. hirsutum f. typicum is often found in higher elevations river valleys (between 1,800 and 3,300m) from southern Ecuador to central Peru. It is a strong outbreeder with a very long exerted stigma. Most PI's are self-incompatible. Those that have permitted selfing produce weak progeny which suffer greatly from inbreeding depression. This subspecies does not readily cross with L. esculentum. The other subspecies, L. hirsutum f. glabratum, easily accomodates self-fertilization and progeny do not suffer from inbreeding depression. It is found in the southwestern parts of Ecuador at lower latitudes (0-6 degrees south). This subspecies is capable of crossing with L. esculentum.

L. hirsutum has been noted for several resistances to pests. One trait is that of resistance to two species of red spider mite. This is a physical rather than a biochemical mechanism. Mites become tangled in sticky substances which are secreted by the glandular hairs (trichomes). L. hirsutum also has a high concentration of a naturally occuring pesticide, 2-tridecacone, in the plant. This provides a high degree of protection against aphids and lepidopteran larvae (caterpillars).

L. hirsutum has also been a source of resistance to pathogens such as early blight (PI 126445), bacterial speck and root-knot nematodes. L. hirsutum f. typicum has also been investigated as a source of cold tolerance.

Late blight horizontal resistance in L. hirsutum. (Lobo, M. and R. Navarro.)
Resistance to potato virus Y and cucumber mosaic virus in Lycopersicon hirsutum. (Gebre-Selassie, K., et.al.)
L. hirsutum fruit, flowers and foliage
Fruit, foliage and flowers
click photo for alternative view of plant
photos courtesy of the Tomato Genetics Resource Center
[photos: Rick, Charles M.]

L. pennellii
syn. Solanum pennellii
Though not considered by some authorities to be a true Lycopersicon species, I will include this species as well. (It is considered to be Solanum pennellii). It is readily crossable to L.esculentum as well. Both self-compatible and self-incompatible types exist. This species evolved in hot, dry enviroments and may prove to be a source of drought resistance and insect tolerance. It is native to coastal areas of Peru and has small green fruit.

Acylsugars of L. pennellii deter feeding and oviposition of the leafminer L. trifolii. (Hawthorne, D.J., et.al.)
Close-up of greenhouse-grown fruits (one per plant) showing variability in morphological features
Close-up of greenhouse-grown fruits (one per plant) showing variability in morphological features.

pennelli in native habitat
L. pennellii plants in native habitat
click for alternate photo
photos courtesy of the Tomato Genetics Resource Center
[photos: Rick, Charles M.]

Desirable traits from other species:

Resistance to race O of Pseudomonas syringae pv. tomato in wild Lycopersicon species. (Bogatsevska, N., Sotirova, V.)
Screening for salintiy tolerance in the genus Lycopersicon. (Hassan, A.A., Al-Afifi, M.A., Matsuda, K., Koto, A. and Itani, S.)
Sources of resistance to fusarium wilt race 3. (Scott, J.W. and Jones, J.P.)

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