Apples
The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family Rosaceae. Linnaeus originally assigned the apple to the genus Pyrus, along with pears and quinces, but the apple was subsequently separated into its own genus. The wild ancestor is Malus sieversii. It has no common name in English. This tree is still found wild in the mountains of Central Asia in southern Kazakhstan, Kyrgyzstan, Tajikistan, and Xinjiang, China.
The apple is one of the most widely cultivated tree fruits. At least 55 million tonnes of apples were grown worldwide in 2005, with a value of about $10 billion. China produced about two-fifth of this total. United States is the second leading producer, with more than 7.5% of the world production. Turkey, France, Italy and Iran are among the leading apple exporters.
The tree is small and deciduous, reaching 5-12 m tall, with a broad, often densely twiggy crown. The leaves are alternately arranged, simple ovals with an acute tip, serrated margin and a slightly downy underside. Flowers are produced in spring, simultaneous with the budding of the leaves. The flowers are white or white with a pink tinge that gradually fades. The fruit matures in autumn, and is typically 5-9 cm diameter (rarely up to 15 cm). The centre of the fruit contains five carpels arranged in a five-point star, each carpel containing one to three seeds.
Apple cultivars
The apple tree was perhaps the earliest tree to be cultivated, and apples have remained an important food in all cooler climates. There are more than 7,500 known cultivars of apples. Different cultivars are available for temperate and subtropical climates. Apples do not flower in tropical climates because they have a chilling requirement.
Commercially popular apple cultivars are soft but crisp. Other desired qualities in modern commercial apple breeding are a colourful skin, absence of russeting, ease of shipping, lengthy storage ability, high yields, disease resistance, apple shape, long stem (to allow pesticides to penetrate the top of the fruit), and popular flavour.
Old cultivars are often oddly shaped, russeted, and have a variety of textures and colours. Many of them have excellent flavour, but may have other problems which make them commercially unviable, such as low yield, liability to disease, or poor tolerance for storage or transport. A few old cultivars are still produced on a large scale, but many have been kept alive by home gardeners and farmers that sell directly to local markets. In the United Kingdom old cultivars such as Cox's Orange Pippin and Egremont Russett are still commercially important even though by modern standards they are low yielding and disease prone.
Although most cultivars are bred for eating fresh (dessert apples), some are cultivated specifically for cooking (cooking apples) or producing alcoholic drinks. Cider apples are typically too tart and astringent to eat fresh, but they give the beverage a rich flavour that dessert apples cannot.
Some breeders have crossed ordinary apples with crabapples or unusually hardy apples in order to produce hardier cultivars. The Excelsior Experiment Station of the University of Minnesota has, since the 1930s, introduced a steady progression of important hardy apples that are widely grown throughout Minnesota and Wisconsin. The most important introductions have included 'Haralson' (which is the most widely cultivated apple in Minnesota), 'Wealthy', 'Honeygold', and 'Honeycrisp'.
Pollination
Apples must be cross-pollinated to develop fruit. Orchard blocks may alternate rows of compatible cultivars, or may have periodic crab apple trees, or grafted-on limbs of crab apple. Some cultivars produce very little pollen, or the pollen is sterile, so these are not good pollenizers.
Symptoms of inadequate pollination are excessive fruit drop (when marble sized), small and misshapen apples, slowness to ripen, and low seed count. Well pollinated apples are the best quality, and will have 7 to 10 seeds. Apples having fewer than 3 seeds will usually not mature and will drop from the trees in the early summer. Inadequate pollination can result from either a lack of pollinators or pollenizers, or from poor pollinating weather at flowering time. It generally requires multiple bee visits to deliver sufficient grains of pollen to accomplish complete pollination.
A common problem is a late frost that destroys the delicate outer structures of the flower. It is best to plant apples on a slope for air drainage, but not on a south facing slope (in the northern hemisphere) as this will encourage early flowering and increase susceptibility to frost.
Growing apples near a body of water can give an advantage by slowing spring warm up, which retards flowering until frost is less likely. However, the cool, humid spring weather in such locations can also increase problems with fungal diseases, notably apple scab; many of the most important apple-growing regions (e.g. northern China, central Turkey, and eastern Washington in the USA) have climates more like the species' native region well away from the sea or any lakes, with cold winters leading to a short, but warm spring with low risk of frost.
Pollination groups
There are four to seven pollination groups in apples depending on climate.
Times in UK
- Group A - Early flowering, May 1 to 3 (Gravenstein, Red Astrachan)
- Group B - May 4 to 7 (Idared, McIntosh)
- Group C - Mid-season flowering, May 8 to 11 (Granny Smith, Cox's Orange Pippin)
- Group D - Mid/Late season flowering, May 12 to 15 (Golden Delicious, Calville Blanc d'Hiver).
- Group E - Late flowering, May 16 to 18 (Braeburn)
- Group F - May 19 to 23 (Suntan)
- Group G - May 24 to 28 (Court Pendu Plat)
One cultivar can be pollinized by a compatible cultivar from the same group or close (A with A or A with B but not A with C or D). Late groups are better to avoid frost in cold areas.
Maturation and harvest
Cultivars vary in their yield and the ultimate size of the tree, even when grown on the same rootstock. Some cultivars, if left unpruned, will grow very large, which allows them to bear a great deal more fruit, but makes harvest very difficult. Mature trees typically bear 40-200 kg of apples each year, though productivity can be close to zero in poor years. Dwarf trees will bear about 10-80 kg of fruit per year.
Pests and diseases
Apple trees are susceptible to a number of fungal and bacterial diseases and insect pests. Nearly all commercial orchards pursue an aggressive program of chemical sprays to maintain high fruit quality, tree health, and high yields. A trend in orchard management is the use of Integrated Pest Management (IPM), which reduces needless spraying when pests are not present, or more likely, are being controlled by natural predators.
Spraying for insect pests must never be done during flowering because it kills pollinators. Nor should bee-attractive plants be allowed to establish in the orchard floor if insecticides are used.
Apples are used as food plants by the larvae of a large number of Lepidoptera species including. Others include Apple maggot and codling moth.
Products
Pests