The peach (Prunus persica) is a tree native to China that bears an edible, sweet, juicy fruit of the same name that is very popular throughout the world. It is a deciduous tree which grows 5–10 meters tall and belongs to the subfamily Prunoideae. Its subgenera, Amygdalus is distinguished from the other subgenera by the corrugated seed shell of the fruit. Nectarines are also considered a type of peach, being of the same species.
While the fruit and flowers of the peach tree provide for the individual purpose of reproduction of the peach species, these and the tree itself also provide for larger purposes for the ecosystem (food and habitat for animals) and for humans (nutritional, commercial, and aesthetic values). For humans, the peach fruit is nutritious, providing vitamins, minerals, fats, proteins, sugars, and other items that promote human health. In addition, the human senses of taste, smell, sight, and touch are all stimulated. The fruit is delicious, the flowers give off an aroma that is very enticing, and the overall shape and color of the tree, flowers, and fruit appeal to the human inner sense of beauty.
The scientific name persica derives from an early European belief that peaches were native to Persia (now Iran). The modern botanical consensus is that they originated in China and were introduced to Persia and the Mediterranean region along the Silk Road in early historical times, probably by about 2,000 B.C.E. (Huxley et al. 1992).
The leaves of the peach tree are simple, alternate, serrated, lanceolate, 7–15 centimeters (cm) long, and 2–3 cm broad. The flowers are produced in early spring before the leaves; they are solitary or paired, 2.5–3 cm in diameter, white to lavender, with five petals.
The peach fruit has a single large seed encased in hard wood (called the "stone" or "pit"). The seed is red, oval shaped and 1.5-2 cm thick. The fruit has yellow or whitish flesh with a delicate aroma and a velvety skin that bruises easily. Peaches, along with cherries, plums, and apricots, are classified as stone fruits or drupes.
There are more than 2,000 different cultivars of peaches, which can be divided into two types, (1) "freestone" and (2) "clingstone" cultivars, depending on whether the flesh sticks to the stone or not. Both kinds can have either white or yellow flesh. Peaches with white flesh typically are very sweet with little acidity, while yellow-fleshed peaches typically have a more acidic taste. Low-acid white-fleshed peaches are the most popular kinds in China, Japan, and neighboring Asian countries, while Europeans and North Americans have historically favored the acidic, yellow-fleshed kinds.
The nectarine is a cultivar group of peach that has a smooth, non-fuzzy skin. Though grocers treat fuzzy peaches and nectarines as different fruits, they belong to the same species. Nectarines have arisen many times from fuzzy peaches, often as bud sports.
Nectarines can be white, yellow, clingstone, or freestone. Regular peach trees occasionally produce a few nectarines, and vice versa. Their flesh is more easily bruised than peaches. The history of the nectarine is unclear; the first recorded mention is from 1616 in England, but they had probably been grown much earlier in central Asia.
Peach fruit contains not only sugar and acids but other nutrients as well. A typical peach of 175 grams contains 16.7 grams of carbohydrate, 0.4 grams of fat, and 1.6 grams of protein (NutritionData 2007). This has a total caloric value of 68. The predominant sugar is sucrose. The main fat is the polyunsaturate linoleic acid. The most abundant amino acids in the proteins are, in descending order, glutamic acid, serine, and hydroxyproline. Several vitamins are also present, including vitamin A (11 percent daily value, based on 2000 calorie diet ), vitamin C (19 percent DV), and niacin (7 percent DV) (NutritionData2007). Peaches are also rich in the minerals potassium, copper, and manganese (NutritionData 2007).
Peach trees grow very well in a fairly limited temperate range. They have a chilling requirement of 33-45 degrees Fahrenheit that subtropical areas cannot satisfy, and on the other hand are susceptible to frost damage. Most U.S. cultivars require 750 to 1,000 hours of chilling in order for the trees to bloom and grow properly (NCSU 2007).
The trees themselves can usually tolerate temperatures to around −26°C to −30°C, although the following season's flower buds are usually killed at these temperatures, leading to no crop that summer. Flower bud kill begins to occur at temperatures between −15°C and −25°C depending on the cultivar and the timing of the cold, with the buds becoming less cold tolerant in late winter (Szalay et al. 2000). Certain cultivars are more tender and others can tolerate a few degrees more cold.
In addition, a lot of summer heat is required to mature the crop, with mean temperatures of the hottest month between 20°C and 30°C.
A problematic issue in many peach-growing areas is spring frost. The trees tend to bloom fairly early in spring, around the same time as daffodils. The blossoms can often be damaged or killed by freezes. If temperatures drop below about −4°C, most blossoms will be killed. However, if the blooms are not fully open, they can tolerate a couple degrees colder temperature.
Important historical peach-producing areas are China, Japan, Iran, Turkey, and other countries in the Mediterranean region, where they have been grown for thousands of years. More recently, the U.S. (California, Colorado, New Jersey, South Carolina, Michigan, Texas, Alabama, Georgia (known as the "Peach State"), Virginia, West Virginia, Maryland, Delaware, Washington, Oregon), Canada (southern Ontario and British Columbia), and Australia (the Riverland region) have also become important.
Most peach trees sold by nurseries are grafted cultivars.
The most important bacterial disease is bacterial spot, which affects the fruit, leaves, and twigs. Planters should try to select a variety that has a high resistance, such as Derby, Pekin, Clayton, and Biscoe. Certain varieties are very susceptible, such as Sunglo, Summer Pearl, Monroe, and Redgold.
Many fungal diseases affect peaches: peach leaf curl, rhizopus rot, brown rot, and peach scab.
One virus, transmitted by nematodes, is known as stem-pitting virus. Other diseases caused by viruses include peach yellows, X-disease, Western X-disease, ring spot, and peach mosaic. These infected trees need to be uprooted and destroyed (World Book 1999).
Several species of mites will attack the foliage resulting in defoliation and abnormal fruit.
Many insects attack peach trees. White peach scale, Pseudaulacaspis pentagona, destroyed an entire orchard of 10,000 trees in Georgia. Stink bugs (family Pentatomidae) and lygus bugs (family Miridae) are sucking insects that attack the fruit and can cause it to drop prematurely or be misshapened.
Peach tree borer (family Sesiidae) is considered by some to be one of the most destructive insects of peaches. They feed under the bark and are attracted to trees that are already diseased or stressed in some way. When a tree shows evidence of brown frass or brown gum around the trunk, this is symptomatic of a borer attack.
Oriental fruit moths (family Tortricidae) attack trees bearing stone fruits. They cause the shoots to die at the terminal or tip.
The plum curculio (family Curculionidae), is a weevil that lays its eggs in the fruit of the peach, as well as many other types of fruit. They may attack the fruit at any time up to about two weeks before harvest.
Another disease, of unknown origin, is called "peach tree short life" disease or PTSL. Different rootstocks are being developed to provide protection.
It is possible to grow a tree from either a peach or nectarine seed. The germinated seed requires a south or west-facing position and regular watering.
Peaches should be located in full sun with good air flow. This allows cold air to flow away on frosty nights and keeps the area cool in summer. Peaches are best planted in early winter, as this allows time for the roots to establish and be able to sustain the new spring growth. When planting in rows, plant north-south. Trees are typically planted 6 to 8 meters apart to give 108 to 180 trees per acre.
A peach orchard begins to bear marketable fruit within 3-4 years after planting. They will reach their peak productivity when they are 8 to 12 years old. A typical healthy peach tree will live 20 years. A good tree can produce up to 550 lbs of peaches a year.
For optimum growth, peach trees require a constant supply of water. This should be increased shortly before the harvest. The best tasting fruit is produced when the peach is watered throughout the season. Drip irrigation is ideal, with at least one dripper per tree. Although it is better to use multiple drippers around the tree, this is not necessary. A quarter of the root being watered is sufficient.
Peach trees, like other fruit trees, do best in deep, well-drained soils with a pH of 6.0 - 6.5. Peaches have a high nutrient requirement, needing more nitrogen than most other fruit trees. A nitrogen, phosphorus, potassium fertilizer can be applied regularly, and an additional mulch of poultry manure in autumn soon after the harvest will benefit the tree. If the leaves of the peach are yellow or small, the tree needs more nitrogen. Blood meal and bone meal, 3–5 kg per mature tree, or calcium ammonium nitrate, 0.5–1 kg, are suitable fertilizers. This also applies if the tree is putting forth little growth.
Peach trees have a tendency to produce too much fruit. The fruit needs to be thinned out in order for the remaining fruit to be of a marketable size and have good flavor. Thinning should be done before the pit hardens or when they have reached 2 cm in diameter, usually about two months after flowering. In dry conditions, extra watering is important. Fresh fruit are best consumed on the day of picking, and do not keep well. They are best eaten when the fruit is slightly soft, having aroma, and heated by the sun.
The flavor of the peach is very unique and consists of many compounds that interact to produce a very delicate aroma and taste sensation that is highly valued throughout the world.
Peach flavor contains aldehydes (including benzaldehyde, pentanal, and hexanal), lactones (including hexalactone, delta, and gamma decalactones), many esters (such as ethyl acetate, butyl acetate, and cis-3-hexenyl acetate), and alcohols (including cis-3-hexenol and linalool) (Riu-Aumatell et al. 2005).
The sweetness of the ripe peach is due primarily to the ratio of sugars to acids. An immature peach is sour and has a high ratio of acid to sugar, but as it reaches maturity the ratio of acid to sugar becomes much lower giving the fruit a very sweet taste.
Peaches are known in China and Japan not only as a popular fruit but for the many folktales and traditions associated with it. Momotaro, one of Japan's most noble mythical heroes, was held to be born from within an enormous peach floating down a stream. Momotaro or "Peach Boy" went on to fight evil oni and face many adventures. The flowers of the flowering peach are admired by the Japanese but not as much as the sakura (cherry).
In China, the peach was said to be consumed by the immortals due to its mystic virtue of conferring longevity on all who ate them. The divinity Yu Huang, also called the Jade Emperor, had a garden of "immortal peaches." Whoever ate one of these peaches lived forever. His mother called Xi Wangmu, or Queen Mother of the West, ensured the gods' everlasting existence by feeding them the peaches of immortality. The immortals residing in the palace of Xi Wangmu were said to celebrate an extravagant banquet called the Pantao Hui or "The Feast of Peaches." The immortals waited six thousand years before gathering for this magnificent feast; the peach tree put forth leaves once every thousand years and it required another three thousand years for the fruit to ripen. Ivory statues depicting Xi Wangmu's attendants often held three peaches.
The peach often plays an important part in Chinese tradition and is symbolic of long life. One example is in the peach-gathering story of Zhang Daoling, who many say is the true founder of Daoism. Elder Zhang Guo, one of the Chinese Eight Immortals, is often depicted carrying a Peach of Immortality. The peach blossoms are also highly prized in Chinese culture, ranked slightly lower than mei blossom.
Due to its delicious taste and soft texture, in ancient China "peach" was also a slang word for "young bride," and it has remained in many cultures as a way to define pretty young women (as in English, with peachy or peachy keen).
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