Apple

An apple is the round, edible fruit of an apple tree (Malus spp.). Fruit trees of the orchard or domestic apple (Malus domestica), the most widely grown in the genus, are cultivated worldwide. The tree originated in Central Asia, where its wild ancestor, Malus sieversii, is still found.^[1]

Etymology

The word apple is derived from Old English æppel, meaning "fruit", not specifically the apple. That in turn is descended from the Proto-Germanic noun *aplaz, descended in turn from Proto-Indo-European *h₂ébōl. As late as the 17th century, the word also functioned as a generic term for all fruit including nuts; one example is the pineapple, the swollen accessory fruit outside of the cashew nut known as the "cashew apple", another is a 14th-century Middle English expression appel of paradis, meaning a banana.^[1]

Description

The apple tree is deciduous, generally standing from 2 to 4.5 metres (6 to 15 feet) tall in cultivation and up to 15 m (49 ft) in the wild, though more typically 2 to 10 m (6.5 to 33 ft). When cultivated, the size, shape and branch density are determined by rootstock selection and trimming method. Apple trees may naturally have a rounded to erect crown with a dense canopy of leaves.^[1]

Fruit

The fruit is a pome that matures in late summer or autumn. The true fruits or carpels are the harder interior chambers inside the apple's core. There are usually five carpels inside an apple, but there may be as few as three.^[1]

Chemistry

Important volatile compounds in apples that contribute to their scent and flavour include acetaldehyde, ethyl acetate, 1-butanal, ethanol, 2-methylbutanal, 3-methylbutanal, ethyl propionate, ethyl 2-methylpropionate, ethyl butyrate, ethyl 2-methyl butyrate, hexanal, 1-butanol, 3-methylbutyl acetate, 2-methylbutyl acetate, 1-propyl butyrate, ethyl pentanoate, amyl acetate, 2-methyl-1-butanol, trans-2-hexenal, ethyl hexanoate, hexanol.^[1]

Taxonomy

The apple as a species has more than 100 alternative scientific names, or synonyms. In modern times, Malus pumila and Malus domestica are the two main names in use. M. pumila is the older name, but M. domestica has become much more commonly used starting in the 21st century, especially in the western world.^[1]

Genome

Apples are diploid, with two sets of chromosomes per cell (though triploid cultivars, with three sets, are not uncommon), have 17 chromosomes and an estimated genome size of approximately 650 Mb. Several whole genome sequences have been completed and made available. The first one in 2010 was based on the diploid cultivar 'Golden Delicious'.^[1]

History

Central Asia is generally considered the center of origin for apples due to the genetic variability in specimens there. The wild ancestor of Malus domestica was Malus sieversii, found growing wild in the mountains of Central Asia in southern Kazakhstan, Kyrgyzstan, Tajikistan, and northwestern 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.^[1]

Breeding

Many apples grow readily from seeds. However, apples must be propagated asexually to obtain cuttings with the characteristics of the parent. This is because seedling apples do not "breed true", instead they are "extreme heterozygotes", i.e. rather than resembling their parents, seedlings are all different from each other and from their parents.^[1]

Pollination

Apples are self-incompatible; they must cross-pollinate to develop fruit. During the flowering each season, apple growers often utilize pollinators to carry pollen. Honey bees are most commonly used.^[1]