Wheat, common name for cereal grasses of a genus of the grass family (see Grasses), cultivated for food since prehistoric times by the peoples of the temperate zones and now the most important grain crop of those regions (see Agriculture).

Wheat is a tall, annual plant attaining an average height of 1.2 m (4 ft). The leaves, which resemble those of other grasses, appear early and are followed by slender stalks terminating in spikes, or so-called ears, of grain.

Classification

Species of wheat are classified according to the number of chromosomes found in the vegetative cell. They are divided into three series: the diploid, or einkorn, containing 14 chromosomes; the tetraploid, or emmer, containing 28 chromosomes; and the hexaploid, containing 42 chromosomes. Wheat species crossbreed relatively frequently in nature. Selection of the best varieties for domestication took place over many centuries in many regions. Today, only varieties of common, club, and durum wheats are of commercial importance, but other species are still grown to suit local conditions, and they provide essential stock for formal breeding programs (see Plant Breeding).

Varieties

According to the regions in which they are grown, certain types of wheat are chosen for their adaptability to altitude, climate, and yield. The common wheats grown in the former Soviet republics, the United States, and Canada are spring and winter wheats, planted either in the spring for summer harvest or in the fall for spring harvest. The color of the grain varies from one type to another; white wheats are mostly winter wheats, red are spring wheats. Closely related to the common wheats are the club wheats, which have especially compact spikes, and spelta (not grown in the United States), in which the glumes (reduced, scalelike leaves) tightly enclose the grains. Durum wheat (Latin durum, "hard") is so called because of the hardness of the grain. It is grown in north-central regions of the United States. New high-yielding wheats were developed in the 1960s for use in developing countries, and research on them continued in the 1970s. Experimental programs have produced commercial wheat varieties for hardiness and disease resistance. In 1978 the identification of a drought-resistant, high-protein, ancestral species growing in the Middle East held promise of still more improved wheat varieties.

Diseases and Planting Methods

Diseases of wheat are connected with parasitic fungi. The principal diseases are rust and smut. Wheat is also liable to injury from several insect pests; a particularly important insect pest is the Hessian fly. See also Diseases of Plants; Fungi; Pest Control.

In the United States wheat is usually planted by sowing machines of the drill or broadcast type. Little cultivation is necessary beyond preparation of the land by plowing, harrowing, and, sometimes, dusting to control pests. Wheat crops are generally rotated with corn, hay, and pasture in the eastern United States and are rotated with oats and barley, or bare fallowing in the drier western regions. See Crop Farming.

Uses

The main use of wheat is in the manufacture of flour for bread and pastries. In general, hard varieties are used for bread flour and soft varieties for pastry flour. Wheat is used also in the production of breakfast foods and to a limited extent in the making of beer, whiskey, and industrial alcohol. Low grades of wheat, and by-products of the flour-milling, brewing, and distilling industries, are used as feed for livestock. A minor amount of wheat is used as a coffee substitute, especially in Europe, and wheat starch is employed as a sizing for textile fabrics. See also Bread; Flour; Macaroni.

History

Remains of both emmer and einkorn wheats have been found by archaeologists working on sites in the Middle East dating from the 7th millennium BC. Emmer was grown in predynastic Egypt; in prehistoric Europe it was grown in association with barley and einkorn and club wheats. Bread wheat was identified at a 6th-millennium BC site in southern Turkistan, and a hexaploid wheat was found at Knossos in Crete. The cultivation of wheat in the Americas was introduced by the Spaniards in Mexico and by the English in New England and Virginia.

Statistics

World output of wheat as the 1990s began was more than 590 million metric tons, an increase of about 30 percent over the average for the period 1979 to 1981. The USSR continued as the world's leading producer, with a near-record 235 million metric tons, but as the central government broke up in 1991, production fell. China was in second place in 1990, the United States in third. Other major wheat producers are India, Canada, France, and Australia.

The leading wheat-producing states in the United States are North Dakota, Kansas, Montana, and Oklahoma. In Canada, wheat farming is centered in Saskatchewan, Alberta, and Manitoba.

Scientific classification: Wheat makes up the genus Triticum of the family Gramineae.

See also Food Supply, World.