Wheat is a temperate crop but is grown on a large scale in a sub-tropical and tropical regions of the world. Africa is however not important for wheat production.
Origin
Wheat is of Asian origin in areas around southern Turkey, Iraq and adjacent territories of Syria and Iran.
The cultivation of wheat spread from its centre of origin of India, Pakistan and China in the east to the Mediterranean countries in the west and to the USSR and other European countries in the north.
It reached Africa through Ethiopia about 5,000 years ago.
Today, wheat is grown in most temperate and subtropical countries; notably Zimbabwe, Ethiopia, Sudan and Kenya.
Ecology
Wheat is the number one cereal of the temperate regions of the world, which are climatically very suitable for its cultivation.
In the tropics, it is grown at higher altitudes or where suitable conditions exist in the lowlands.
It is grown in such areas only during the winter season or harmattan period. As the harmattan period is dry in the northern region of west Africa, it is grown under irrigation.
Wheat can be grown successfully under a wide range of rainfall and temperature conditions.
It grows successfully in hot climates if the humidity is not too high.
It is not well adapted to areas where warm, humid conditions prevail, largely because such conditions favor rapid development of diseases.
For the proper development of the wheat plant, the best temperature range is 20-23°C but optimum temperature for good tillering is 16-20°C.
Wheat can be grown successfully under a wide range of soil conditions, but it is best adapted to fertile, well-drained silt and clay loam soils.
Botany
The roots are adventitious and arise from basal nodes of the stem and its main branches.
The leaves are arranged alternately at the nodes, the blade is long and narrow with parallel veins.
The leaves have no petiole (they are sessile).
Primary lateral branches (or tillers) arise from buds in the axils of the basal leaves of the main stem, and secondary laterals arise from the basal nodes of the primary ones.
Each plant normally produces 2-3 tillers under typical crowded field conditions, but individual plants in fertile soils with ample space may produce as many as 30-100 tillers.
The internodes of the main stem and its tillers do not elongate during the vegetative phase of growth, resulting into the tufted crown form.
The elongation of internodes occurs with the initiation of the terminal inflorescence primordia.
The young inflorescences are carried upwards by the developing stems or culms and finally emerge from within the encircling sheath of the last leaf.
The flowers or florets are small and are arranged in characteristic cluster known as spikelets.
The floret consist of a bract-like lemma and palea which enclose three stamens and a unilocular gynaecium which has one ovule and style with feathery stigmas.
The awn arises dorsally on the tip of the lemma in awned types.
The grain is a one-seeded fruit with a dry indehiscent pericarp known as the caryopsis. T
The starchy endosperm constitutes about 82-88% of the dry weight of the grain.
The average spike (head) of wheat contains 25-30 grains in 14-17 spikelets. Large spikes may contain 50-75 grains.
Cultural practices
The optimum time for sowing is decided by several factors. The most important of which is the temperature during the growing season.
In Nigeria for example, the middle to end of November has been found to be the most suitable time for sowing.
The seed-rate is 90-100kg/ha if good quality seed and the seeds should be dressed with Aldrex-T.
The seeds can be drilled in 60cm rows. The rows could be spaced closer (20-30cm) for improved high yielding dwarf varieties.
The thick sowing of wheat in narrow row spacing does not permit mechanical weeding.
Under intensive farming, the use of herbicides is the most suitable method of controlling weeds.
Bentazon at 1.2kg a.I/ha or Chlorbromuron at 1.5kg a.I./ha can be applied post mergence at 4-5 weeks after planting. NPK 15.15.15 can be applied at planting at the rate of 200-300 kg/ha and top dressed with urea at 50 kg N/ha.
Harvesting
Wheat planted in mid November matures in February/ March. The crop usually ripens about 30 days after the blooming of the florets.
The kernels are completely filled when they reach the dough stage, at which time the leaves, stalks and spikes begin to lose their green color and become golden yellow.
The kernels should be allowed to dry to a safe moisture content of 12%.
Harvesting may be done by hand with sickles or by machine.
On a small scale, threshing is done by a thresher or beating against a hard surface, followed by winnowing to separate the grain from the chaff. With a combine, harvesting and threshing are done together.
Yields
Farmers’ yield range from 900 to 1900 kg/ha of dry grain. By adopting improved practices, yields can be increased to 3000 kg/ha. The potential yield of wheat is up to 6000 kg/ha.
Storage
For good storage, dry grains to 10% moisture content to reduce damage by storage pests. Fumigation of grain stores is desirable.
Chemical composition
The grain of wheat contains approximately 70% carbohydrate, 11.5% protein, 2% fat, 2% fibre, 1.5% ash and 13% water.
Uses
- The flour is used for products such as bread, pastries, cakes, crackers, macaroni, and spaghetti.
- It is used in the manufacture of dextrose, alcohol, starch, gluten , malt etc.
- By-products from processing of wheat, such as bran, are high in protein content and serve as livestock feeds.
- The straw provides a valuable fodder.
- It is also used for making baskets and hats, thatching and as packing materials.
Diseases
- Black rust is caused by Puccinia graminis. Yellow rust is caused by P. striiformis distinguished by deep cadmium yellow color of the pustules, which are closely crowded together in parallel lines. Control of rusts is by use of resistant cultivars.
+Smuts can also cause considerable losses in wheat. There are two types is smut diseases-covered smut caused by Tilletia caries and loose smut caused by Ustilago nuda.
Insect pests
The main insect pests of wheat are wheat stem sawflies, hesian flies, aphids and cutworms.
