Tomato Fast Facts

Heirloom tomatoes

Origin & US Production
Tomato (Solanum lycopersicum) is a member of the Solanaceae or nightshade family. It is a native plant of Central and South America including the Andes Mountains. Tomatoes did not gain popularity in Europe and North America as a food until late 1800s because it was considered to be poisonous. The US is one of the largest producers of tomatoes worldwide. The estimated farm-gate value of tomato production is US$2B (ERS). California is a primary region for tomato cultivation, boasting 100 growers and production acreage of 37,000 acres. Tomato production in California in 2003 generated revenue of $925M. Major California growing regions include the San Joaquin, Salinas, and Imperial Valleys, and Ventura and San Diego Counties.

Nutrition
Fresh tomatoes are an excellent source of Vitamins A and C. Carotenoids and lycopene may act as anticarcinogens and have been of great interest to researchers. Interestingly, cooked or processed tomato products have higher concentrations of lycopene, making pastes and sauces valuable sources of this compound. Note however that there is a trade-off because vitamins (especially vitamin C) are lost during processing.

Adapted from MA Stevens (1986) “The future of the field crop” In: The Tomato Crop (ed) JG Atherton, J Rudich pp. 570

Postharvest Considerations
Tomatoes are classified into two types&emdash;fresh market and processing tomatoes. Fresh market tomatoes are eaten directly, and as such differ in composition, method of harvest and postharvest handling. Fresh market tomatoes have higher sugar and acid content while processing tomatoes have greater levels of ethanol insoluble solids.

Harvest of fresh-market tomatoes is more labour intensive and expensive compared to that of processing tomatoes. It can cost $4,000 to $6,000 per acre for fresh market tomato production. The conditions under which tomatoes are harvested, stored and ripened is the culmination of many years of research to provide optimum fruit to the consumer, free of mechanical damage, disease, bright red colour and firm texture. Fruit is often picked when green to reduce damage and uniform ripening is normally achieved by storing the fruit in defined temperature under ethylene gas (100-150 ppm). These fruit often have a longer postharvest life, but consumers find that they have a poorer flavour than tomatoes ripened naturally on the vine.

Tomato as a Model Genetic System
Tomatoes have benefited from a long history of genetic improvement and UC Davis has a grand tradition in the breeding and development of new tomato varieties. The two model plant genetic species for which a fully sequenced genome is available&emdash;Arabidopsis and Rice make a much reduced or dehiscent fruit and are largely unsuitable for understanding processes related to fleshy fruit development. Here are some features that make tomato particularly useful as a research material.

L. pimpinellifolium—a wild species of tomato that can be crossed with modern tomatoes for introgression of desirable traits. Image taken from Tomato Genetic Resource Centre database.

  • Tomato species are self-compatible and exclusively inbreeding.
  • Tomato is diploid with 12 chromosomes.
  • Excellent collection of exotic germplasm exists. The Charlie Rick Tomato genetic Resource Centre housed at UC Davis holds one of the most extensive catalogues of diverse tomato germplasm.
  • Sequencing of the gene rich regions of the tomato genome is in progress. http://www.sgn.cornell.edu/about/tomato_sequencing.pl
  • Inter-specific crosses between wild and cultivated Lycopersicon species is possible and have provided a route to introduce novel traits into modern species.
  • A well characterized mutant population is available and is useful for forward genetic screens. http://zamir.sgn.cornell.edu/mutants/
  • Tomato is relatively easy to transform. http://ucdptf.ucdavis.edu/services.shtm
  • Compared to many species it has a relatively small genome (9 Mb).
  • There are well developed cytogenetic maps. http://www.sgn.cornell.edu/cview/map.pl?map_id=13
  • Transcriptomic and metabolomic tools are available. http://ted.bti.cornell.edu/

Fruit of a wild species of tomato compared to a modern tomato variety bred for large fruit. From Frary et al (2000) Science 7 vol 289 no 5478. 85.

Growth Habit
Tomatoes are further classified based on their growth habit. Determinate, semi-determinate and indeterminate varieties have distinct patterns of growth which affects harvest index, time to harvest and nutritional value of the fruit. Determinate varieties have a set life cycle. They have short, compact, bushy vines. Fruit clusters on these vines are concentrated at the ends of short branches and the growing season is short. Indeterminate varieties normally have a long growing season. They produce branching systems that can grow indefinitely. Once flowering has been initiated it will continue throughout the life of the plant, and fruit production can be very high. Vegetative growth of indeterminate plants continues for several months and require pruning; they characteristically have large, sometimes sprawling, vines. Semi-indeterminate varieties have characteristics intermediate to the fully determinate and indeterminate lines.