|Malus domestica - The domestic food apple fruit, ripe on an apple tree branch.|
|Varieties in this species|
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- Cultivation: Low-Maintenance, Easy-To-Grow, For-Gardeners
- Light: Sun
- Soil: Rich, Mid-Fertility, Loam, Clay
- pH: 7
- Moisture: Medium, Dry, Well-Drained
- Form: Tree, Shrub
- Habit: Deciduous
- Flower: Small
- Fruit/Seed: Large, Fruit.Nut, Green, Yellow, Red
- Foliage: Leaves, Green
- Uses: Edible, Ornamental, Craft, Industrial
Small to medium sized tree with spreading canopy, to 30 ft in wild, generally 6-15 ft in cultivation. Tree size and shape is heavily dependent on rootstock and training system (see below). Leaves elliptical with serrate margins, dark green with light pubescence on underside. Flowers
Petals are white when open, but have red-pink undersides when opening, hence the "pink" bloom stage. The ovary is inferior, embedded in the floral cup or hypanthium, containing 5 locules, usually 2 ovules per locule. The inflorescence is a cyme of 4-6 flowers, with the center flower opening first; the central flower is often called the "King bloom", and has the potential to produce a larger fruit than other flowers. Flowers are produced terminally from mixed buds (containing both leaves and flowers) on spurs, or to a lesser extent on long shoots. Spurs form on 2-yr-old and older wood, and generally grow only a fraction of an inch each year.
Most cultivars are commercially self-unfruitful. Cross-incompatibility is rare, and most cultivars that bloom at the same time and are not sports of each other will serve as pollinizers, including crabapples. Single apple trees produce some fruit when self-pollinated because most cultivars are not totally self-incompatible. A few cultivars are pollen-sterile (e.g., 'Jonagold', 'Winesap', and 'Mutsu'). Honey bees are the most effective pollinator. Fruit
A special fruit type is given to apple and related fruits - the pome. The bulk of the fleshy edible portion derives from the hypanthium or floral cup, not the ovary. Seeds are relatively small and black, and mildly poisonous. Fruiting begins 3-5 years after budding, although a few fruit may be produced in the 2nd year. This varies with rootstock (dwarfing = more precocious) and cultural practices (excessive pruning = delay). Fruit are usually thinned to 1 per spur, with spurs spaced 4-6 inches apart for attainment of marketable size. Apples are generally thinned with chemicals such as the insecticide Sevin, or the synthetic auxins NAA and NAAm.
Soils and Climate Deep, well-drained, loamy soils with pH 6-7 are best, but apples are grown on a wide variety of soils worldwide.
Apples are adaptable to various climates, but can be considered best adapted to the cool temperate zone from about 35-50° latitude. They have a more northern range than many other tree fruits due to relatively late blooming and extreme cold hardiness. Apples reach maturity about 120-150 days after bloom, with some cultivars maturing in as short as 70 days, and others as long as 180 days.
Several methods are available for determining optimal harvest time. Days from full bloom is relatively constant from year-to-year, and gives growers a rough estimate of picking date. Cultivars like 'Gala' mature early and 'Fuji' very late. Target values of firmness vary by cultivar and intended storage method, with firmer fruit reserved for long-term storage.
Apples must be picked by hand to avoid bruising and reduction of fresh market quality grade. Fruit must be picked carefully to avoid damaging the spur, where next season's fruit will be borne.
Standard packing line operations are used for apples after harvest - hydrocooling, washing, culling, waxing, sorting, and packing (Figure 12). Apples are packed most often in 4/5 bushel boxes (40 lbs), but polyethylene bags (5-10 lbs) are also popular for retail marketing. Quality grade is based on size and appearance of skin; greater prices are obtained for larger fruit and those with minimal surface blemishes.
Controlled atmosphere (CA) storage has allowed the marketing of apples on a year round basis. The storage room atmosphere is altered to retard respiration by reducing oxygen to 2-3%, and raising CO2 to about 1%. Firmer, less ripe fruit are placed in long-term CA (150-365 days), while more mature fruit are sold directly or placed in short-term storage.
The center of diversity of the genus Malus is the eastern Turkey, southwestern Russia region of Asia Minor. Apples were probably improved through selection over a period of thousands of years by early farmers. Alexander the Great is credited with finding dwarfed apples in Asia Minor in 300 BC; those he brought back to Greece may well have been the progenitors of dwarfing rootstocks. Apples were brought to North America with colonists in the 1600's, and the first apple orchard on this continent was said to be near Boston in 1625. From New England origins, apples moved west with pioneers, John Chapman (alias Johnny Appleseed) and missionaries during the 1700's and 1800's. In the 1900s, irrigation projects in Washington state began and allowed the development of the multi-billion dollar fruit industry, of which the apple is the leading species.
The genome sequence of the domesticated apple (Malus × domestica), shows a relatively recent (>50 million years ago) genome-wide duplication (GWD) has resulted in the transition from nine ancestral chromosomes to 17 chromosomes in the Pyreae. Traces of older GWDs partly support the monophyly of the ancestral paleohexaploidy of eudicots. Phylogenetic reconstruction of Pyreae and the genus Malus, relative to major Rosaceae taxa, identified the progenitor of the cultivated apple as M. sieversii. Expansion of gene families reported to be involved in fruit development may explain formation of the pome, a Pyreae-specific false fruit that develops by proliferation of the basal part of the sepals, the receptacle. In apple, a subclade of MADS-box genes, normally involved in flower and fruit development, is expanded to include 15 members, as are other gene families involved in Rosaceae-specific metabolism, such as transport and assimilation of sorbitol.
The domesticated apple (Malus × domestica Borkh., family Rosaceae, tribe Pyreae) is the main fruit crop of temperate regions of the world. Here we describe a high-quality draft genome sequence of the diploid apple cultivar 'Golden Delicious'. Domesticated apple genotypes are all highly heterozygous, imposing technical challenges in genome sequencing and assembly1 while allowing identification of a very large set of SNPs2.
Rosaceae belong to the rosids, which include one-third of all flowering plants3. Whereas the haploid (x) chromosome numbers of most Rosaceae are 7, 8 or 9, Pyreae have a distinctive x = 17. Pyreae have long been considered an example of allopolyploidization between species related to extant Spiraeoideae (x = 9) and Amygdaleoideae (x = 8), although a within-lineage polyploidization event has also been hypothesized4.
In addition, we examine the genetic variability in Rosaceae and related taxa, comparing Pyreae species, Rosaceae tribes and two rosid families. Gene content and order of the assembled chromosomes indicate that both recent and old GWDs have occurred. We provide a model describing the evolution of the Pyreae genome, including Malus, and offer insights into the origin of the domesticated apple.