Many fruits are nutritious as well as appetizing. For example, oranges and strawberries contain large amounts of vitamin C. Most fruits have a high sugar content, and so they provide quick energy. Fruits alone cannot provide a balanced diet, however, because the majority of them supply little protein.
The world's fruit growers raise millions of tons of fruit annually. Fruit growing is a branch of horticulture, a field of agriculture that also includes the raising of nuts, vegetables, flowers, and landscape crops. Most nuts are actually fruits, as are the edible portion of such vegetables as cucumbers, green peppers, and tomatoes. To prevent confusion, horticulturists define a fruit as an edible seed-bearing structure that (1) consists of fleshy tissue and (2) is produced by a perennial. A perennial is a plant that lives for more than two years without being replanted. The horticultural definition of a fruit excludes nuts and vegetables. Nuts are firm rather than fleshy. Most vegetables are annuals-that is, the plants live for only one season.
In some cases, the horticultural definition of a fruit conflicts with the definition used by botanists and with common usage. For example, watermelons and muskmelons are fruits, and most people regard them as such. But they grow on vines that must be replanted annually, and so horticulturists regard melons as vegetables. Rhubarb is sometimes considered a fruit because of its use as a dessert. But people eat the rhubarb leafstalk, not the seed-bearing structure. Therefore, horticulturists classify rhubarb as a vegetable.
How horticulturists classify fruits
Most of the fruits that are widely raised in North America were originally brought from other regions. For example, apples, cherries, and pears originated in Europe and western Asia. Apricots and peaches first came from China, and lemons and oranges from China and Southeast Asia. All these fruits are now grown in any part of the world that has a favorable climate.
Most fruit plants require considerable amounts of moisture. Dates and olives are among the few fruits that can be grown in dry regions without irrigation.
Horticulturists classify fruits into three groups, based on temperature requirements for growth: (1) temperate fruits, (2) subtropical fruits, and (3) tropical fruits.
Temperate fruits must have an annual cold season to grow properly. They are raised chiefly in the Temperate Zones, the regions between the tropics and the polar areas. Most temperate fruits are grown in Europe and North America, but Asia and Australia also have major producing areas.
The principal temperate fruits are apples, apricots, cherries, peaches, pears, and plums. In addition, most small fruits, which grow on plants smaller than trees, are raised mainly in the Temperate Zones. They include blueberries, cranberries, grapes, raspberries, and strawberries.
Subtropical fruits require warm or mild temperatures throughout the year but can survive an occasional light frost. They are grown chiefly in subtropical regions.
The most widely grown subtropical fruits are the citrus group, which includes grapefruit, lemons, limes, and oranges. Oranges, the leading citrus crop, are grown throughout the subtropics, from southern Japan to southern Europe. In the United States, Florida produces by far the most oranges. Other subtropical fruits include dates, figs, olives, and avocados.
Tropical fruits are raised mainly in the tropics and cannot stand even a light frost. Bananas and pineapples, the best-known tropical fruits, are grown throughout the tropics, and much of each crop is exported. Other tropical fruits include acerolas, cherimoyas, litchis, mangoes, mangosteens, and papayas.
Almost all species of fruits grow on plants that have a woody stem. Such plants are trees, bushes, or woody vines. Fruits that grow on trees include apples, cherries, lemons, limes, oranges, and peaches. Most small fruits grow on bushes, but grapes come from woody vines. Bananas and strawberries grow on plants that have a nonwoody stem.
Fruit crops, unlike most other crops, are not grown from seeds. Plants grown from seeds may vary in many ways from generation to generation. But growers strive to produce plants that will bear fruits of uniform type, appearance, and quality. Such fruits bring the highest prices when marketed. Fruit plants produce fruits of uniform quality if grown vegetatively-that is, from certain parts of desirable plants, such as stems, buds, and roots. The part that is grown develops new tissues and new parts identical to those of the parent plant.
Fruit plants are produced vegetatively in three main ways: (1) by grafting, (2) from cuttings, and (3) from specialized plant structures. Most fruit trees are reproduced by grafting. In this process, a bud or piece of stem from one tree is joined to a rootstock from another. A rootstock is a root or a root plus its stem. The resulting tree will have most of the same characteristics as the tree from which the bud or stem was taken. However, the rootstock may determine such characteristics as the size and productivity of the new tree.
Some fruit plants are produced from cuttings or from specialized structures. Most cuttings are pieces of stem that grow roots when placed in water or moist soil. Specialized structures called runners are used to grow strawberry plants. Runners are long, slender shoots that mature strawberry plants send out along the ground. A runner placed in soil develops into a new plant.
Some fruit growers produce their own plants vegetatively. However, most growers buy their plants from nurseries that specialize in producing them.
The branch of horticulture that deals with fruit growing is called pomology. Pomologists have developed highly efficient methods of planting and caring for fruit crops, and most fruit farms use these techniques.
There are three main steps in growing fruit: (1) planting, (2) caring for the crop, and (3) harvesting.
Planting. Fruit crops are perennials, and so they do not have to be replanted annually as do most other crops. After the original planting, a fruit farmer need only replace plants that become unproductive. Many fruit plants remain productive for 30 to 50 years or even longer. In mild climates, farmers generally plant trees, bushes, and vines in fall. In cold climates, planting usually takes place in spring.
Most bushes are planted from 3 to 5 feet (0.9 to 1.5 meters) apart in rows that are 6 to 10 feet (1.8 to 3 meters) apart. Rows of grapevines are spaced about 10 feet (3 meters) apart. In the past, farmers almost always grew full-sized fruit trees. In most cases, the trees were planted from 20 to 40 feet (6 to 12 meters) apart to allow room for growth. Today, many farmers prefer to grow dwarf trees, which are planted close together. The branches of each tree may grow up a supporting framework called a trellis. The trellis enables all the fruit to receive maximum sunlight, and so the crop ripens better and faster than it otherwise would. Fruit is also easier to harvest from dwarf trees than from full-sized trees.
Caring for the crop. Most fruit growers use special machinery to fertilize, cultivate, and otherwise care for their crops. Fruit crops must be fertilized at least once a year. Some fertilizers are applied to the soil, and others are sprayed on the plants. Many fruit growers cultivate the soil around young fruit plants periodically. This practice helps control weeds and thus encourages crop growth. Most fruit crops grown in extremely dry regions must be irrigated. Farmers use various methods, such as ditches and sprinklers, to distribute irrigation water.
In many cases, the branches of a young fruit tree must be trained so that the tree develops a uniform shape and a sturdy structure. Training may involve propping the trunk or tying the branches, or it may consist entirely of pruning. Pruning strengthens a plant by ridding it of unproductive branches. Nearly all fruit plants have to be pruned at least once annually. In addition, most farmers remove some of the crop from the trees during the early stages of the fruit's growth. This practice, called thinning, helps increase the size of the remaining fruit.
The majority of fruit growers use chemical pesticides to protect their crops against diseases and insect pests. Most pesticides are sprayed or dusted on crops by tractor-driven machinery or specially equipped light airplanes or helicopters. Plant breeders have also developed varieties of fruit plants that resist certain diseases and harmful insects.
Sudden spring frosts can endanger fruit crops in temperate or subtropical regions. Farmers use water distributed by sprinklers to protect small-fruit crops from frosts. Water releases heat as it freezes. If it is sprinkled onto the crops continuously, it keeps the tender flowers and young fruits from freezing. Farmers use heaters to protect tree crops from spring frosts.
Harvesting. Most fruits ripen rapidly after reaching their mature size. Harvesting occurs during different stages of the growth process, depending on the type of fruit and its intended use. For example, gooseberries and cherries used in making artificial coloring are harvested when immature. Apples, bananas, peaches, and pears are usually harvested when mature, but before they ripen. Berries and most fruit picked at home orchards are harvested during the ripening stage. Most fruits taste best when they are allowed to ripen on the plant. Citrus fruits do not go through a distinct ripening process and may be harvested over a long period of time after they mature. Fruits are bruised more easily than most other crops, and so they must be harvested with greater care. Most are picked by hand. However, the increasing cost of hand labor has encouraged the use of fruit-harvesting machines. Some of these machines have arms that shake the fruit loose from the plants. The loosened fruit drops onto outstretched cloths. Other mechanical pickers have fingers that "comb" fruit from the plants.
The United States is the leading fruit-producing country in the world. It raises more than 10 percent of all the apples, pineapples, and plums; about 20 percent of the lemons, oranges, peaches, and strawberries; and about 45 percent of the grapefruit. California is the nation's chief fruit-growing state. Other leading states include Florida, Michigan, New York, Oregon, and Washington.
Most fruit scheduled to be sold fresh is taken from the orchard or field by truck and delivered to a packing house. Many large fruit farms have their own packing facilities. Commercial packing houses are centrally located in fruit-growing regions. Most large packing houses are fully mechanized. Machines wash the fruit, sort it according to size and quality, and pack each batch into containers. The fruit is then shipped to market or stored for future delivery. Railroads and trucks carry most overland shipments of fruit. Most overseas shipments travel by ocean freighter.
Fruits can be stored for varying lengths of time under controlled conditions. Temperate tree fruits must be stored at temperatures near freezing. Some kinds of apples can be kept fresh for about a year under such conditions. On the other hand, most small fruits remain fresh only a few days or weeks in cold storage. Tropical and subtropical fruits can be stored for a few weeks or months under temperature-controlled conditions. The temperatures, though cool, must be well above freezing. The amount of oxygen ordinarily present in the air promotes spoilage of fruit. The storage time for all fruits can be lengthened by reducing the oxygen supply.
Much fruit is shipped directly from farms to food processors. Processing plants preserve fruit by such methods as canning, drying, and freezing.
Developing new varieties of fruit
Over the centuries, fruits have been improved by constant selection of the most desirable plants. In selection, plants grown from seed are examined for various desirable qualities. Individual plants are singled out for high productivity or for the superior color, texture, or flavor of their fruits. If the desirable characteristics of the selected plant are reproduced when the plant is grown vegetatively, the selection may be classed as a new cultivated variety. Cultivated varieties are also known as cultivars.
Occasionally, an individual plant develops an unexpected characteristic due to a mutation, a random genetic change. For example, an apple tree may suddenly start to bear fruit of a more intense red color. Horticulturists refer to such a mutation as a sport. Growers have used sports to develop many improved varieties of fruit. The trees of Delicious apples originally produced pale-colored, striped fruits. Some branches on individual trees began to bear solid-red apples. By grafting these branches onto appropriate rootstocks, growers produced the attractively colored types of Delicious apples available today.
Horticultural plant breeders use a technique called crossing or hybridization to improve fruits. In this process, pollen is taken from a plant that has been selected for a particular desirable trait. The pollen is placed in the flower of a plant selected for another desirable quality. Some of the plants grown from the resulting seed may have the desirable characteristics of both parents. Occasionally, one of these plants may prove worthy of being named as a new variety. In many cases, hybridization and selection are repeated over many generations to create a new variety. Hybridization is a highly useful technique because it enables breeders to produce varieties with combinations of more and more desirable qualities. In the future, desirable characteristics may be transferred using techniques of genetic engineering that remove genes from one plant and insert them into another.