الوصف

The cultivation of wheat (Triticum spp.) reaches far back into history. Wheat was one of the first domesticated food crops and for 8 **0 years has been the basic staple food of the major civilizations of Europe, West Asia and North Africa. Today, wheat is grown on more land area than any other commercial crop and continues to be the most important food grain source for humans. Its production leads all crops, including rice, maize and potatoes.

Although the crop is most successful between the latitudes of *0° and *0°N and *7° and *0°S , wheat can be grown beyond these limits, from within the Arctic Circle to higher elevations near the equator.

Development research by the International Maize and Wheat Improvement Center (CIMMYT) during the past two decades has shown that wheat production in much warmer areas is technologically feasible.

In altitude, the crop is grown from sea level to more than 3 **0 masl, and it has been reported at 4 **0 masl in Tibet.

The optimum growing temperature is about *5°C, with minimum and maximum growth temperatures of 3° to 4°C and *0° to *2°C, respectively. Wheat is adapted to a broad range of moisture conditions from xerophytic to littoral.

Although about three-fourths of the land area where wheat is grown receives an average of between **5 and **5 mm of annual precipitation, it can be grown in most locations where precipitation ranges from **0 to 1 **0 mm.

Optimal production requires an adequate source of moisture availability during the growing season; however, too much precipitation can lead to yield losses from disease and root problems.

Cultivars of widely differing pedigree are grown under varied conditions of soil and climate and show wide trait variations. Although wheat is being harvested somewhere in the world in any given month, harvest in the temperate zones occurs between April and September in the Northern Hemisphere and between October and January in the Southern Hemisphere.

Classification into spring or winter wheat is common and traditionally refers to the season during which the crop is grown. For winter wheat, heading is delayed until the plant experiences a period of cold winter temperatures (0° to 5°C). It is planted in the autumn to germinate and develop into young plants that remain in the vegetative phase during the winter and resume growth in early spring. This provides the advantage of using autumn moisture for germination and making effective use of early spring sunshine, warmth and rainfall.

Spring wheat, as the name implies, is usually planted in the spring and matures in late summer but can be sown in autumn in countries that experience mild winters, such as in South Asia, North Africa, the Middle East and the lower latitudes.

Wheat is special in several ways. Wheat is grown on more than **0 million ha, larger than for any other crop, and world trade is greater than for all other crops combined. The raised bread loaf is possible because the wheat kernel contains gluten, an elastic form of protein that traps minute bubbles of carbon dioxide when fermentation occurs in leavened dough, causing the dough to rise. It is the best of the cereal foods and provides more nourishment for humans than any other food source.

Wheat is a major diet component because of the wheat plant's agronomic adaptability, ease of grain storage and ease of converting grain into flour for making edible, palatable, interesting and satisfying foods.