Cultivar

Cultivar Definition

A cultivar is a subspecies classification describing plants varieties which are produced through artificial selection. Cultivar, the word, comes from a combination of cultivated variety. Different forms of the same species are considered varieties. When these varieties are then artificially selected by humans for particular traits, they become a cultivar.

Cultivar is a term recognized internationally, and more formally defined as certain plants which can be distinguished from others by any characteristic. In reproducing a cultivar either sexually or asexually, these characteristics always remain “true”. This mean that the characteristics are controlled by a homozygous gene for that cultivar. In this case, the plant can self-fertilize, which will produce plants that are also homozygous for particular traits. The alternative is that the line is maintained through vegetative propagation, also known as cloning.

Either way, an established line with defined characteristics becomes a cultivar. A cultivar is narrower than a species or a group, and represents one of the narrowest focuses, genetically speaking. Many cultivars, because they are so closely related, can produce hybrids with other cultivars of the same species. This allows an almost never ending variety of cultivars to be produced from only a few starting cultivars. In the United States “cultivar” is more or less synonymous with “variety”.

Cultivar Development

Cultivars have been developed for thousands of years, since humans first started artificially selecting plants. The first true cultivars were the first well-established lines of crop plants. These included rice, corn, beans, wheat, and other vegetables. These cultivars survived for millennia and formed the basis of modern civilizations. As such, a well-established, true-breeding cultivar always has a higher value than an unknown seed.

To this end, many organizations have been established throughout the world to certify various lines as being a true cultivar. Further, governments and academia have pulled together to fund and develop many more cultivars. Many modern cultivar vegetables have been produced in the last century through selective breeding and advances in plant propagation. Many modern cultivar vegetables and fruits have a history of both historical artificial selection and newer, more scientific advances to the many cultivars of the species. Below is an image of wild cabbage.

Wild cabbage is found in costal and southwestern Europe, while its cultivars are found globally. Wild cabbage has been cultivated for thousands of years, since the times of Ancient Greece. There, it was grown in gardens in several varieties, which mainly differed in the shape of the leaves. Each cultivar was then put through thousands of years of artificial selection. The end of this process left dozens of cultivars, each less like the original plant. Here is a shortened list of just some of the wild cabbage cultivars:

But that’s not the end! While these used to be individual cultivars, these are now known as groups, another subspecies identifier. The actual cultivars of wild cabbage now have even more distinct names, such as King Cole cabbage. These lines were created from a single cultivar which had desirable characteristics. Future progeny of these plants were selected to start the new lines which “bred true”, in that they would consistently produce these features.

This, along with modern advancements such as genetic modification, have developed an entire new generation of cultivar plants. Some of these have modifications which improve the plant’s resistance to drought, disease, or insects. Other cultivar varieties grow a particular type of flower, or have enlarged leaves or roots. A cultivar can be maintained through a line of seeds, but this is not easy. Any cross-pollination or mutation within the seeds can allow other genetics to arise, which will change the properties of the plant. A cultivar that is maintained in a line through the seeds must be segregated to prevent cross-pollination. The plants must have an ability to self-fertilize to complete this process. Many flowers, vegetables, grains, and other such crops are maintained in this way.

Other plants, such as fruit trees, grape vines, and other woody ornamental plants are easier to propagate through cloning. In this process, a small piece of the plant is harvested and established in a growing media. Over time, the small bundle of cells differentiates into a fully formed plant, and can be transplanted outside. This also allows the formation of a cultivar which is not homozygous for a certain trait. Using this method, a difficult to breed and grow species can be maintained as a cultivar. Otherwise, entire groves of fruit trees would have to be grown indoors to keep them from becoming pollinated. This is simply not realistic, as trees grow very slowly and need an enormous amount of space and energy.

While many of the above cultivar plants may seem similar to each other, it may strike you to know that potatoes and tomatoes belong to the same genus of plants! These cultivated varieties produce entirely different products, from the same historical plant. It is amazing what artificial selection can accomplish in such a short timeframe.

Cultivar Nomenclature

It is important to note that true cultivars, today, are specific “brand names” of larger groups. For instance Bing cherries, or Rocky Ford Cantaloupe. These are specific varieties of the cherry and cantaloupe which have defining characteristics. Each cultivar has been established and can be consistently reproduced. The progeny always have the same characteristics.

Whether you think of Gala apples or Savoy cabbage, each of these is a cultivar of a larger group, which is a subset of a species. The nomenclature of such a complicated relationship can get complicated. However, below is a simple formula to help understand if you are talking about the species, group, or cultivar. The full scientific name of each cultivar should be in this format.

Scientific name (Group name) ‘Cultivar name’

A good example is King Cole cabbage. In this case, cabbage is a group within the species Brassica oleraceae. Therefore, the entire name of King Cole cabbage should look like this:

Brassica oleraceae (Capitata) ‘King Cole’

The part in italics represent the genus and species. Remember that this is the same species that produces broccoli, kale, and cauliflower. Capitata, which is always shown in parenthesis, is the group name. Capitata is the group for all cabbage cultivars, which includes a wide variety. Finally, each cultivar is distinguished by a unique epithet, in this case “King Cole”. This is often the name of the scientist responsible or the family behind the funding.

Quiz

1. Which of the following cultivar varieties are most related? (Multiple Select)
A. Brassica oleracea (Capitata) ‘Green’
B. Brassica oleracea (Botrytis) ‘Romanesco’
C. Malus pumila ‘Gala’

2. Which of the following statements is FALSE?
A. A cultivar is an artificially created stable line of a particular species
B. A species can contain multiple cultivars
C. Each cultivar is its own species

3. A farmer finds a new plant on his property. He decides to harvest and eat it. Is this a new cultivar?
A. No
B. Yes
C. Maybe…

References

• Hartwell, L. H., Hood, L., Goldberg, M. L., Reynolds, A. E., & Silver, L. M. (2011). Genetics: From Genes to Genomes. Boston: McGraw Hill.
• McMahon, M. J., Kofranek, A. M., & Rubatzky, V. E. (2011). Plant Science: Growth, Development, and Utilization of Cultivated Plants (5th ed.). Boston: Prentince Hall.
• University of Illinois Extension. (2018, May 8). Cabbage. Retrieved from Watch Your Garden Grow: https://extension.illinois.edu/veggies/cabbage.cfm