Introduction to major field crops (1+1)

Origin

The growing of wheat began very early in the pre-historic period so long ago that the origin of wheat is still a matter of speculation. DeCondollebelieved that wheat is originated in the valley of Euphrates and Tigris. Later spread over to China, Egypt and other parts of the world. In India,evidences from Mohan-jo-daro excavations indicate that wheat was cultivated here more than 5,000 years ago.

Distribution
Wheat is most widely cultivated all the cereals. It is commonly grown in North American continent, Latin American including Europe, West Asia, North Africa, SouthAfrica, East Africa, South Asia and Australia. In India, Uttar Pradesh, Punjab, Madhya Pradesh, Rajasthan, Bihar and Haryana are the main wheat producing states.

Classification
Wheat belongs to family Gramineae (Poaceae) and the genus Triticum. Although as many as 18 species of wheat have been described and recognized, commonly cultivated species are Triticummonococcum(Einkaran wheat), Triticumdicoccum(Emmerwheat), Triticumduram(Duramwheat) Triticumvulgare/aestivum(Common wheat).

Climatic Requirement
Wheat is cultivated over a wide range of latitudes ranging between 600 N to 600 S, altitudes ranging from the sea level to an elevationup to 3,500 m in the tropics and sub tropics. Normally, the most ideal conditions for wheat growth are cool and moist weather during vegetative growth period and warm and dry weather during grain formation. Because of this reason the great wheat regions of the world are found in the temperate zones between 30-60oN and 25-40oS.

The optimum temperature for the germination of wheat is between 20-22oC, vegetative growth 16-22oC and grain development maximum temperature of about 25oC. The annual rainfall ranges between 250 and 1800 mm. Low as well as high rainfall is detrimental to wheat yield. Short days increase the vegetative growth of wheat, whereas, longer days hasten the formation of inflorescence.