A food grain crop. Wheat is the most widely grown food crop in the world, and is increasing in production. It ranks first in world crop production and is the national food staple of 43 countries. At least one-third of the world's population depends on wheat as its main staple. The principal food use of wheat is as bread, either leavened or unleavened. The United States is second to Russia in total production, but the average yield per acre in the United States is about twice that of Russia. Other major wheat-producing countries in the world are Canada, China, India, France, Argentina, and Australia.

Wheat is best adapted to a cool dry climate, but is grown in a wide range of soils and climates. Much of the world's wheat is seeded in the fall season and, after being dormant or growing very slowly during winter, it makes rapid growth in the spring and develops grain for harvest in early summer.

Wheat for milling is classified according to hardness, color, and best use. In the United States, there are seven official market classes of which the following five are the most important: (1) hard red winter, for bread; (2) hard red spring, for bread and rolls; (3) soft red winter, for cake and pastries; (4) white, for bread, breakfast foods, and pastries; and (5) durum, for macaroni products.

The wheat inflorescence is a spike bearing sessile spikelets arranged alternately on a zigzag rachis. Two, three, or more florets may develop in each spikelet and bear grains. The grain may be white, red (brown), or purple, and it may be hard or soft in ture. Size of the grain or caryopsis may be large, as in durum, or very small, as in shot wheat (Triticum sphaerococcum). Wheats vary in plant height and in the ability to produce tillers. The stems are usually hollow. The wheat grain is composed of the endosperm and embryo enclosed by bran layers. The endosperm portion is principally starch and is therefore used as energy food. Wheat is also an important protein source, especially for those people who use wheat as their main staple. Seed

Botanically, wheat is a member of the grass family to which rice, barley, corn, and several other cereal grain crops also belong. The Triticum genus includes a wide range of wheat forms. Taxonomic studies place the goat grasses (Aegilops) and wheat (Triticum) in one genus, Triticum. Wheat has been crossed with rye (Secale) and with Agropyron (a grass). New forms, called Triticale, have been derived from crossing rye and wheat followed by doubling the chromosomes in the hybrid.

Most countries in which wheat is grown have wheat breeding programs in which the objective is to develop more productive and more stable varieties (cultivars). Many methods are combined in these programs, but in nearly all of them specially selected parent types are crossbred followed by pure-line selection among the progeny to develop new combinations of merit. Varieties and genetic types from all over the world become candidate parents to provide the desired recombinations of good quality, winter and drought hardiness, straw strength, yield, and disease resistance. Wheats must be bred for specific milling processes and to provide quality end-use products. Many new varieties have complex pedigrees. Breeding (plant) Grain crops

Milling of wheat has evolved from rudimentary crushing or cracking to sophisticated separation and refining. The main purpose of milling is isolation of the starch-protein matrix, that is, separation of the endosperm from the high-fiber bran and high-lipid germ. Under optimal conditions, milling yields a high-quality, uniformly colored flour with a relatively stable shelf-life. The flours of hard wheats (11 to 13% protein) develop strong gluten complexes during mixing and are therefore suitable for making bread. Whole soft wheats (9 to 11% protein) yield flours that are used primarily for cakes, cookies, and pastries. Durum wheat is used to produce a relatively coarse flour, semolina, used for manufacture of pasta products.