Above Image: A group of tomatoes with differing shapes, sizes and colours.

Taxonomy

Tomato, along with pepper, potato, and eggplant, belong to the Solanaceae family of flowering plants. This family of plants are also known as nightshades. Nightshades include more than 3000 species including many that are economically important. Even though there are more than 7000 varieties of tomatoes, they all represent only one species of tomato that is cultivated, S. lycopersicum.

What's in a Name?

Tomatoes have had several scientific names over the years including Solanum lycopersicum and Lycopersicon esculentum. Why the different names, you might ask? The reason for this has to do with how people thought tomatoes were related to other plants. In the early 1700s, Linnaeus put tomatoes in the genus Solanum based on their visible characteristics. In the mid-1700s, Philip Miller, another botanist, did not agree with Linnaeus' classification and instead placed tomatoes into the genus Lycopersicon. He thought that tomatoes belonged in a different genus from other poisonous nightshade species. More recently, taxonomists reclassified the species again, putting them back into the genus Solanum based genetic information. What this story about the classification of tomatoes goes to show is that scientific knowledge is not static, and that scientific knowledge constantly changes based on new information.

Origins

Wild tomato plants originated in the Andean region of South America, which is today known as Peru, Bolivia, Chile, and Ecuador. It is believed that tomatoes were first grown by the Aztecs and Incas as early as 700 A.D. The tomatoes that were grown at that time were very different in size and taste from the tomatoes that we know today (see Figure 1).

It is not known exactly how or who brought tomato seeds to Europe, but in the 16^th century, references to tomatoes began to appear. Further domestication occurred throughout Europe in the 18^th and 19^th centuries.

There is no clear evidence for how the tomato was introduced to North America, but it is believed to have occurred sometime in the 16^th or 17^th century. By the middle of the 18^th century, tomatoes were cultivated, but not widely consumed in the United States. This was because people believed that tomatoes were poisonous since they belonged to the nightshade family. It has been reported that in the early 1800, an American publicly consumed tomatoes showing the audiences that they were not poisonous. After it was established that tomatoes were not poisonous, tomatoes were still slow to gain popularity because many people found them too acidic for their taste.

Domestication

Tomatoes come in many different shapes, colours, and sizes (see Figure 2). Variation in tomatoes has resulted from natural means and with the help of humans, through artificial selection (also known as selective breeding). Tomatoes have been bred by humans for many characteristics such as yield, shelf-life, pest resistance, taste, fruit size and shape, colour, seed size and weight, and nutritional quality.

By the end of the 19^th century, tomatoes were bred by many farmers and gardeners. They were able to keep the seeds from the tomatoes they produced and plant them from year to year to grow more plants. This practice of seed saving has led to what we now call Heirloom tomato varieties. These plants produce tomatoes with amazing variations in shape, size, and colour. Heirloom varieties are true breeding and therefore keep the same traits as the parent plants.

With the start of commercial breeding in the beginning of the 20^th century, hybrid tomato varieties appeared. Hybrid tomatoes are the offspring from the cross-breeding of two different tomato varieties. Hybrids often have the best traits from each of the parent plants, which make them highly desired. Commercial farmers, growing hybrid tomatoes, are discouraged from using their own seeds and are required to purchase seeds from a seed company. This is to make sure that the tomato quality is consistent for grocery stores and food processors.

Tomato Genetics

More recently, due to advances in genomics, scientists are finding out more about which genes are responsible for a certain characteristics, such as the colour and size. Scientists have also been able to create new tomato varieties through genetic engineering. This can be done in many ways. But generally, the genes are changed so that the trait or characteristic that the scientists are looking for can be observed in the plant.

One famous example of a genetically engineered tomato is the 'FlavrSavr', which became the first commercially available genetically engineered tomato in 1994. With genetic engineering this tomato cultivar did not ripen as fast or soften as quickly as a conventional tomato, making it easier to harvest and transport without damage. The 'FlavrSavr' tomato was ultimately not profitable because it was costly to produce and distribute. It also received negative media attention because it was a genetically engineered organism, which resulted in its removal from the market. Although there are no genetically engineered tomatoes grown commercially in the world today, plant breeders are continuously working on other ways to help select for desirable traits in tomatoes. The recent sequencing of the genome of the tomato cultivar 'Heinz 1706', in 2012, will help with future tomato breeding efforts.

Glossary

Artificial selection

Also known as selective breeding. This is the intentional breeding of a plant or animal in order to select for specific character traits, i.e. colour, size, shape of the tomato, etc.

Class

Used in classifying living organisms. Examples of classes include dicot and monocot plants.

Cultivar

In plants, this is a variety that has been produced by artificial selection.

Division

Used in classifying living organisms. Examples of divisions include flowering plants or angiosperms.

Domestication

Adapting wild plants or animals for human use.

Family

Used in classifying living organisms. An example of a family is the Solanaceae or nightshade family.

Gene

A region of DNA that contains the information which determines the characteristics or traits of a living thing.

Genetic engineering

Genetic modification using a laboratory technique that allows the direct addition or removal of a gene.

Genome

The complete set of genes in an organism.

Genomics

The study of genomes.

Genus

Used in classifying living organisms. An example of this is the genus Solanum, to which tomatoes belong.

Heirloom tomato varieties

The seeds of these plants are passed down from generation to generation and are a result of true breeding. These plants are allowed to pollinate without human help.

Hybrid tomato varieties

These are offspring from the cross-breeding of two different tomato varieties that often have the best traits from each of the parent plants.

Kingdom

Used in classifying living organisms. An example of this is the kingdom Plantae or plants.

Linnaeus

Carl Linnaeus (1707-1778) was a Swedish botanist who is considered by many to be 'the father of taxonomy.' He created the naming system for classifying all living things that is the basis for how we classify organisms today. To learn more about Linnaeus and his taxonomy, read the backgrounder:

Order

Used in classifying living organisms. An example of this is the order Solanales, which contains the nightshade family.

Species

Used in classifying living organisms. A species is a group of organisms that are able to breed with each other and produce offspring. For more information about what makes a species, read the backgrounder:

Taxonomy

The identification, naming, and classification of living things.

References

• About the Solanaceae Family - Sol Genomics Network (Accessed January 29, 2016). This article discusses various members of the nightshade family.
• The case of the FLAVR SAVR tomato - University of California, California Agriculture (Accessed February 1, 2016). This article discusses the history behind the introduction of the 'FlavrSavr' tomato.
• Classification for Kingdom Plantae Down to Family Solanum L. - USDA Natural Resources Conservation Service (Accessed February 16, 2016). This website provides information about the classification system for the nightshades.
• Domestication and Breeding of Tomatoes: What have We Gained and What Can We Gain in the Future? - Annals of Botany (Accessed January 28, 2016). This article discusses the history of tomato domestication and breeding.
• The History of Tomatoes in America - Grit (Accessed February 16, 2016). This article discusses the history of the introduction and cultivation of tomatoes in North America.
• Hybrid vs. GMO vs. Heirloom - Bonnie Plants (Accessed February 1, 2016). This article compares different tomato varieties.
• Miller, Phillip - Encyclopedia.com (Accessed February 16, 2016). This article describes the biography of this botanist.
• The Original Genetically Modified Tomato You'll Never Eat Again - Gizmodo (Accessed February 16, 2016). This website discusses the story of the 'FlavrSavr' tomato.
• Phylogeny - Solanaceae Source (Accessed February 16, 2016). This article discusses the groupings within the nightshade family.
• Solanum lycopersicum L. - ITIS Report (Accessed February 16, 2016). This website provides information about various scientific names and the classification system for tomato.
• Tomatoes - GMO Compass (Accessed February 2, 2016). This article discusses the history of the 'FlavrSavr' tomato.
• Tomatoes' Genetic History - Wild to Salad (Accessed January 28, 2016). This article discusses the history of tomato domestication and evolution by breeding.
• The tomato genome sequence provides insights into fleshy fruit evolution - Nature (Accessed February 16, 2016). This website describes the sequencing of the tomato genome.

External Resources

• Tomato Genetics Resource Centre - University of California Davis (Accessed January 28, 2016). This website provides information about how to grow tomato plants, identify them, and many other resources for keeping healthy plants.
• Tomato Varieties - Rutgers, New Jersey Agricultural Experiment Station (Accessed January 28, 2016). This website provides information about many tomato varieties, including photos.
• Who was Linnaeus? - The Linnaean Society (Accessed January 28, 2016). This article describes the life of Carl Linnaeus.