Apple

An **apple** is an edible fruit produced by an **apple tree** (***Malus domestica***). Apple trees are cultivated worldwide and are the most widely grown species in the genus *Malus*. The tree originated in Central Asia, where its wild ancestor, *Malus sieversii*, is still found today. Apples have been grown for thousands of years in Asia and Europe and were brought to North America by European colonists. Apples have religious and mythological significance in many cultures, including Norse, Greek and European Christian tradition.

Apple trees are large if grown from seed. Generally, apple cultivars are propagated by grafting onto rootstocks, which control the size of the resulting tree. There are more than 7,500 known cultivars of apples, resulting in a range of desired characteristics. Different cultivars are bred for various tastes and use, including cooking, eating raw and cider production. Trees and fruit are prone to a number of fungal, bacterial and pest problems, which can be controlled by a number of organic and non-organic means. In 2010, the fruit's genome was sequenced as part of research on disease control and selective breeding in apple production.

Worldwide production of apples in 2018 was 86 million tonnes, with China accounting for nearly half of the total.

## Etymology

The word "apple", formerly spelled *æppel* in Old English, is derived from the Proto-Germanic root \*ap(a)laz, which could also mean fruit in general. This is ultimately derived from Proto-Indo-European \*ab(e)l-, but the precise original meaning and the relationship between both words is uncertain.

As late as the 17th century, the word also functioned as a generic term for all fruit other than berries but including nuts—such as the 14th century Middle English word *appel of paradis*, meaning a banana. This use is analogous to the French language use of *pomme*.

## Description

The apple is a deciduous tree, generally standing 2 to 4.5 m (6 to 15 ft) tall in cultivation and up to 9 m (30 ft) in the wild. When cultivated, the size, shape and branch density are determined by rootstock selection and trimming method. The leaves are alternately arranged dark green-colored simple ovals with serrated margins and slightly downy undersides.

Blossoms are produced in spring simultaneously with the budding of the leaves and are produced on spurs and some long shoots. The 3 to 4 cm (1 to 1 1⁄2 in) flowers are white with a pink tinge that gradually fades, five petaled, with an inflorescence consisting of a cyme with 4–6 flowers. The central flower of the inflorescence is called the "king bloom"; it opens first and can develop a larger fruit.

The fruit matures in late summer or autumn, and cultivars exist in a wide range of sizes. Commercial growers aim to produce an apple that is 7 to 8.5 cm (2 3⁄4 to 3 1⁄4 in) in diameter, due to market preference. Some consumers, especially those in Japan, prefer a larger apple, while apples below 5.5 cm (2 1⁄4 in) are generally used for making juice and have little fresh market value. The skin of ripe apples is generally red, yellow, green, pink, or russetted, though many bi- or tri-colored cultivars may be found. The skin may also be wholly or partly russeted i.e. rough and brown. The skin is covered in a protective layer of epicuticular wax. The exocarp (flesh) is generally pale yellowish-white, though pink or yellow exocarps also occur.

### Wild ancestors

The original wild ancestor of *Malus domestica* was *Malus sieversii*, found growing wild in the mountains of Central Asia in southern Kazakhstan, Kyrgyzstan, Tajikistan, and Xinjiang, China. Cultivation of the species, most likely beginning on the forested flanks of the Tian Shan mountains, progressed over a long period of time and permitted secondary introgression of genes from other species into the open-pollinated seeds. Significant exchange with *Malus sylvestris*, the crabapple, resulted in current populations of apples being more related to crabapples than to the more morphologically similar progenitor *Malus sieversii*. In strains without recent admixture the contribution of the latter predominates.

### Genome

In 2010, an Italian-led consortium announced they had sequenced the complete genome of the apple in collaboration with horticultural genomicists at Washington State University, using 'Golden Delicious'. It had about 57,000 genes, the highest number of any plant genome studied to date and more genes than the human genome (about 30,000). This new understanding of the apple genome will help scientists identify genes and gene variants that contribute to resistance to disease and drought, and other desirable characteristics. Understanding the genes behind these characteristics will help scientists perform more knowledgeable selective breeding. The genome sequence also provided proof that *Malus sieversii* was the wild ancestor of the domestic apple—an issue that had been long-debated in the scientific community.

## History

Malus sieversii is recognized as a major progenitor species to the cultivated apple, and is morphologically similar. Due to the genetic variability in Central Asia, this region is generally considered the center of origin for apples. The apple is thought to have been domesticated 4000-10000 years ago in the Tian Shan Mountains, and then to have travelled along the Silk Road to Europe, with hybridization and introgression of wild crabapples from Siberia (M. baccata (L.) Borkh.), Caucasus (M. orientalis Uglitz.), and Europe (M. sylvestris Mill.). Only the M. sieversii trees growing on the western side of Tian Shan Mountains contributed genetically to the domesticated apple, not the isolated population on the eastern side.

Chinese soft apples, such as M. asiatica and M. prunifolia, have been cultivated as dessert apples for more than 2000 years in China. These are thought to be hybrids between M. baccata and M. sieversii in Kazakhstan.

Among the traits selected for by human growers are size, fruit acidity, color, firmness, and soluble sugar. Unusually for domesticated fruits, the wild M. sieversii origin is only slightly smaller than the modern domesticated apple.

At the Sammardenchia-Cueis site near Udine in Northeastern Italy, seeds from some form of apples have been found in material carbon dated to around 4000 BCE. Genetic analysis has not yet been successfully used to determine whether such ancient apples were wild Malus Sylvestris or Malus Domesticus containing Malus sieversii ancestry. It is generally also hard to distinguish in the archeological record between foraged wild apples and apple plantations.

There is indirect evidence of apple cultivation in the third millennium BCE in the Middle East. There was substantial apple production in the European classical antiquity, and grafting was certainly known then. Grafting is an essential part of modern domesticated apple production, to be able to propagate the best cultivars; it is unclear when apple tree grafting was invented.

Winter apples, picked in late autumn and stored just above freezing, have been an important food in Asia and Europe for millennia. Of the many Old World plants that the Spanish introduced to Chiloé Archipelago in the 16th century, apple trees became particularly well adapted. Apples were introduced to North America by colonists in the 17th century, and the first apple orchard on the North American continent was planted in Boston by Reverend William Blaxton in 1625. The only apples native to North America are crab apples, which were once called "common apples". Apple cultivars brought as seed from Europe were spread along Native American trade routes, as well as being cultivated on colonial farms. An 1845 United States apples nursery catalogue sold 350 of the "best" cultivars, showing the proliferation of new North American cultivars by the early 19th century. In the 20th century, irrigation projects in Eastern Washington began and allowed the development of the multibillion-dollar fruit industry, of which the apple is the leading product.

Until the 20th century, farmers stored apples in frostproof cellars during the winter for their own use or for sale. Improved transportation of fresh apples by train and road replaced the necessity for storage. Controlled atmosphere facilities are used to keep apples fresh year-round. Controlled atmosphere facilities use high humidity, low oxygen, and controlled carbon dioxide levels to maintain fruit freshness. They were first used in the United States in the 1960s.