Apple Tree

The apple tree (Malus domestica) is a deciduous tree in the rose family best known for its sweet, pomaceous fruit, the apple. It is cultivated worldwide as a fruit tree, and is 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 traditions.

The apple is a deciduous tree, generally standing 1.8 to 4.6 m (6 to 15 ft) tall in cultivation and up to 39 ft (12 m) in the wild.[3]When cultivated, the size, shape and branch density is determined by rootstock selection and trimming method. The leaves arealternately arranged dark green-colored simple ovals with serrated margins and slightly downy undersides.[4]

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 (1.2 to 1.6 in) flowers are white with a pink tinge that gradually fades, five petaled, with an inflorescenceconsisting 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.[4][5]

The fruit matures in late summer or autumn, and varieties exist with a wide range of sizes. Commercial growers aim to produce an apple that is 7.0 to 8.3 cm (2.75 to 3.25 in) in diameter, due to market preference. Some consumers, especially those in Japan, prefer a larger apple, while apples below 5.7 cm (2.25 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 although many bi- or tri-colored varieties may be found.[6] The skin may also be wholly or partly russeted i.e. rough and brown. The skin is covered in a protective layer ofepicuticular wax,[7] The flesh is generally pale yellowish-white,[6] though pink or yellow flesh is also known.

Wild ancestors

Main article: Malus sieversii

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.[4][8] 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 to be more related to crabapples than to the more morphologically similar progenitor Malus sieversii. In strains without recent admixture the contribution of the latter predominates.[9][10][11]

Genome

In 2010, an Italian-led consortium announced they had decoded the complete genome of the apple in collaboration with horticultural genomicists at Washington State University,[12] using the Golden delicious variety.[13] It had about 57,000 genes, the highest number of any plant genome studied to date[14] and more genes than the human genome (about 30,000).[15] This new understanding of the apple genome will help scientists in identifying genes and gene variants that contribute to resistance to disease and drought, and other desirable characteristics. Understanding the genes behind these characteristics will allow scientists to perform more knowledgeable selective breeding. Decoding the genome 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.[16]