Wheat in the world
B.C. Curtis

The cultivation of wheat (Triticum spp.) reaches far back into history. Wheat was one of the first domesticated food crops and for 8 000 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 30° and 60°N and 27° and 40°S (Nuttonson, 1955), 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 (Saunders and Hettel, 1994) has shown that wheat production in much warmer areas is technologically feasible. In altitude, the crop is grown from sea level to more than 3 000 masl, and it has been reported at 4 570 masl in Tibet (Percival, 1921).

The optimum growing temperature is about 25°C, with minimum and maximum growth temperatures of 3° to 4°C and 30° to 32°C, respectively (Briggle, 1980). 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 375 and 875 mm of annual precipitation, it can be grown in most locations where precipitation ranges from 250 to 1 750 mm (Leonard and Martin, 1963). 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 (Percival, 1921).

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 240 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 (Hanson et al., 1982). 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. Doughs produced from bread wheat flour differ from those made from other cereals in their unique viscoelastic properties (Orth and Shellenberger, 1988). Wheat is the most important source of carbohydrate in a majority of countries. Wheat starch is easily digested, as is most wheat protein. Wheat contains minerals, vitamins and fats (lipids), and with a small amount of animal or legume protein added is highly nutritious. A predominately wheat-based diet is higher in fibre than a meat-based diet (Johnson et al., 1978).

Figure 1.1
Worldwide wheat area and production

Source: CIMMYT, 1996.

Wheat is also a popular source of animal feed, particularly in years where harvests are adversely affected by rain and significant quantities of the grain are made unsuitable for food use. Such low-grade grain is often used by industry to make adhesives, paper additives, several other products and even in the production of alcohol.

PRODUCTION AND TRADE

World wheat production increased dramatically during the period 1951-1990, although the expansion of the area sown to wheat has long ceased to be a major source of increased wheat output (CIMMYT, 1996) (Figure 1.1). Production reached an all time high of 592 million tonnes in 1990 and has been 500 million tonnes or above since 1986 when 529 million tonnes was produced. Since 1990, production has remained relatively constant. The share of wheat output from high-income countries has fallen from about 45 percent in the early 1950s to about 35 percent in recent years. Policy changes toward crop reserve programmes to preserve soils have taken considerable production area from wheat in high-income countries. In the past five years, developing countries have produced more than 45 percent of the world’s wheat.

Figure 1.2
Wheat yields worldwide, 1951-1995

Source: CIMMYT, 1996.

Most of the increase in world wheat production resulted from greater yield per hectare (Figure 1.2). In 1951, world production was nearly 1 tonne/ha. It reached 2 tonnes/ha by the early 1980s and climbed to nearly 2.5 tonnes/ha by 1995. Yields have world2Bread wheat: improvement and production33 continued to climb with little suggestion of a trend reduction. Both genetically improved cultivars for yield and better cultural methods have contributed to the yield increases, but it is difficult to quantify the effects of each. Yield stability has increased substantially across environments largely due to the adoption of management-responsive, high-yielding, disease-resistant semidwarf wheat cultivars (usually referred as HYVs) throughout much of the world, particularly in developing countries. Improved agronomic practices also played an important role in enhancing the dependability and sustainability of yields. In Turkey, for example, production nearly doubled from 9 to about 17.5 million tonnes between 1971 and 1982. This impressive increase resulted primarily from the use of water-conserving cultural practices on the Anatolian Plateau (Curtis, 1982; Dalrymple, 1986). The use of production inputs, primarily nitrogen fertilizer and irrigation water, has risen dramatically. India and China are two major wheat-producing countries where these inputs have dramatically increased. In China, the yield of all cereals increased from 1.4 to 4.6 tonnes/ha from 1961 through 1995, and during the same period, yields in India doubled from 1.0 to 2.1 tonnes/ha (Borlaug and Dowswell, 1996; CIMMYT, 1996).

Wheat-producing countries

Table 1.1 contains a list of the major wheat-producing countries of the world, along with information on average area, yield, production, net imports and consumption during the period 1993-1995. China has the largest land area devoted to wheat production, followed closely by the United States, India and the Russian Federation. Kazakhstan and Canada, ranking fifth and sixth, produce wheat on about half the area of the top four countries. In recent years, China with an average production of more than 100 million tonnes annually ranks far ahead of the United States and India, each averaging near 60 million tonnes. Production increases in China have been dramatic in recent years; production in 1995 was 3 percent higher than in 1994.

Among the larger land area producers, China's yield was 3.5 tonnes/ha, while the United States, India and Russian Federation produced 2.5, and 1.5 tonnes/ha, respectively.

TABLE 1.1
Selected wheat statistics for specified countries. 1993-1995

^a1992-1994 data.
Source: CIMMYT, 1996.

World trade

Although most wheat is consumed within the country where it is produced, roughly one-fifth of the annual crop is exported. World wheat trade was estimated at 108 million tonnes in 1995, most of which was imported by developing countries. Despite increase in production during the past three decades, developing countries account for two-thirds of all wheat imports, which is up from less than half in 1961. China, the world’s largest wheat producer, is also the world’s largest wheat importer, averaging more than 10 million tonnes annually since 1980 (CIMMYT, 1996). Other countries importing more than 5 million tonnes annually include the Russian Federation, Egypt, Japan and Brazil.

The United States, Canada, France and Australia continue to be the largest exporting countries, ranging from 32.7 to 10.2 million tonnes, respectively. Except for France, the wheat imported from these high-income countries is usually a quality product purchased to supplement and enhance the use-potential of locally grown wheat. Canada is considered an important source of high-quality, high-protein wheat for importing countries. The United States produces a wide range of hard and soft wheat possessing grain protein ranging from 7 to 8 percent in soft wheat to 19 to 20 percent in hard wheats (Johnson et al., 1978).

Wheat utilization

World wheat utilization or consumption, defined as food, feed, seed and processed uses, as well as waste, has remained near 550 million tonnes since 1990. Consumption worldwide has increased rapidly since the early 1960s. Wheat consumption in developing countries rose 35 percent during the period 1963-1976. This primarily resulted from increased urbanization and an associated shift in tastes and preferences to wheat over rice and coarse grains, such as maize and sorghum. Also important was the increased adoption of wheat as a food in countries that had consumed little wheat in the past. The influence of urbanization on wheat consumption was most clearly seen in sub-Saharan Africa where per caput consumption growth rates in the late 1970s and early 1980s exceeded 6 percent annually. Annual consumption growth rates in those areas have now decelerated to near zero or less, while average per caput consumption remains near 10 kg/year. Urban consumers tend to prefer convenience-type foods that require little or no preparation (Curtis, 1982). From the mid-1980s to the present, the annual growth of wheat consumption in all developing countries has decelerated from about 5 percent to less than 2 percent. In high-income countries with mature food wheat markets, changes in consumption take place slowly over time and are driven by population growth and changing dietary preferences (CIMMYT, 1996).

WHEAT AROUND THE WORLD

North America

United States

Wheat area, production and yield levels in the United States have remained relatively stable during the past 40 or more years, with wheat prices reflecting most changes in area. Growth rate in wheat yield and in rate of production continues a slow but steady increase, characteristic of a mature market. Five classes of wheat are grown (Table 1.2) in four regions. Most US wheat is grown in the Great Plains from Texas to North Dakota. The area of wheat production during the period 1993-1995 (Table 1.1) was about 25 million ha, with an annual production averaging 62.6 million tonnes. Average yield for the period was 2.5 tonnes/ha.

TABLE 1.2
Classes of wheat produced in the United States

Source: USDA.

Five principal classes of wheat are grown: hard red winter (HRW), hard red spring (HRS), soft red winter (SRW), white and durum (Table 1.2). Most HRW wheat is grown in the central and southern Great Plains states; most HRS wheat is grown in the northern Great Plains states; and practically all SRW wheat is grown in the east. White wheat is grown primarily in the Pacific Northwest and white winter wheat in two eastern states, Michigan and New York. Most durum wheat is grown in the northern Great Plains, primarily North Dakota; some durum is grown in southern California and Arizona. There has been recent interest in growing hard white wheat in the central states of the Great Plains. About 41 percent of the total US wheat production is of the HRW class.

Canada

Wheat is the major crop grown in Canada. The southern areas of the Prairie Provinces of Manitoba, Saskatchewan and Alberta produce about 95 percent of all Canadian wheat (Peterson, 1965). The winters are long and cold, and summers are short and hot. Rainfall is limited and variable in distribution, and droughts are common. Low precipitation restricts yield but is an important factor in producing grain that is high in protein and of high baking quality. Because of its quality, Canadian HRS wheat has a high export demand by countries needing to improve the baking properties of their flour products.

Due to the severe winters in the Prairie Provinces, most of the wheat produced is HRS. A small amount of HRW wheat is grown in southern Alberta along with some irrigated soft white spring wheat. Soft white winter and a small amount of SRW wheat are grown in the eastern provinces. Durum wheat, an important export commodity, is grown on about 5 percent or less of the area in the Prairie Provinces.

Canada exported an average of 84 percent of its wheat in the period 1993-1995. Average wheat consumption during that period was 269 kg/caput, compared with 125 kg/caput in the United States (Table 1.1).

Mexico and Central America

The only countries with significant wheat production in this region are Mexico and Guatemala. During the period 1993-1995, Mexico harvested 930 000 ha/year, while Guatemala harvested 23 000 ha. Area harvested in Mexico grew at the rate of 1.9 percent/year from 1948 to 1985, but the area declined by a total of 2.4 percent during the decade 1986-1995. Rate of growth in wheat production from 1951 to 1985 had a steady increase of 6.2 percent, but since then the growth rate has declined by 2.6 percent. The growth rate of tonnes per hectare yield averaged an increase of 4.2 percent/year from 1948 to 1985 (CIMMYT, 1996). A significant amount of the increase can be attributed to the introduction of high-yielding, semi-dwarf and disease-resistant wheats during the early 1960s (Dalrymple, 1986). Per caput consumption has been near 55 kg/caput since 1951. The increase of population from 73.9 to 93.7 million people from 1982 to 1995 has necessitated increased net imports averaging 1 427 million tonnes in the period 1992-1994.

Wheat makes up about 10 percent of the total cereal area in Mexico of which 90 percent is bread wheat and 10 percent durum wheat. Practically all wheat is grown under irrigation, the majority of which is in the states of Sonora and Sinaloa. The Bahia region of the central plateau produces about 100 000 ha, and some rainfed wheat is produced in the highlands. Leaf rust (Puccinia triticina [syn. P. recondita]) and stem rust (P. graminis) can cause serious yield reductions if infections occur on susceptible cultivars as young plants. Use of resistant cultivars has been fairly successful in control of the rusts, particularly with stem rust. Leaf rust is highly heterogeneous, and more difficulty is encountered in maintaining genetic resistance through breeding. Stripe rust (P. striiformis), Septoria nodorum blotch and Septoria tritici blotch (Leptosphaeria nodorum and Mycosphaerella graminicola), barley yellow dwarf virus (BYDV) and scab (Fusarium spp.) are often a problem in the highlands (Briggle and Curtis, 1987).

In Guatemala, wheat is produced in highland valleys under rainfed conditions, and yields average about 1.1 tonnes/ha (Table 1.1). Diseases adversely affect the crop under the usually wet production conditions. These diseases include: Septoria nodorum blotch and Septoria tritici blotch, scab, stripe rust, BYDV and tan spot (Pyrenophora tritici-repentis [Died.] Drechs.). Weeds are also a significant constraint to production.

South America

Andean region

The total amount of wheat produced in the Andean countries of Bolivia, Peru, Colombia, Ecuador and Venezuela was only about 355 000 tonnes on 301 000 ha during the 1993-1995 period. Yields ranged from 0.3 tonnes/ha in Venezuela to 2.0 tonnes/ha in Colombia. Average per caput consumption during the period 1992-1994 for the region was 45 kg/year, ranging from 26 kg in Ecuador to 73 kg in Bolivia. With a 101.1 million population, the region imported an average of 37.5 million tonnes or about 42 kg/caput from 1992 to 1994. In spite of government intervention attempts to increase wheat area and production in the region in recent years, only marginal gains of 1 to 2 percent have been made for these objectives since 1985.

Production constraints are moisture availability, diseases, poor cultural practices and a general lack of necessary inputs, such as fertilizers, pesticides and farm implements. Rainfall is highly variable from year to year in both amount and distribution. Much improved cultivars have been developed for the region, but seed availability and distribution continues to be a problem for most areas. Improved cultural techniques have been developed for some areas, but the technology transfer to producers has been minimal due to limited budgets and consequent lack of infrastructure to utilize trained technicians.

Southern Cone region

Between 7 and 10 million ha of wheat are grown in the large Southern Cone region, largely in Argentina and Brazil. In the period 1993-1995, Argentina averaged 4 812 million ha, while Brazil averaged 1 278 million ha. During that period, Argentina’s yield average was 2.1 tonnes/ha and Brazil’s was 1.5 tonnes/ha. Wheat area in both countries has been reduced since 1985, 0.9 percent in Argentina and 12 percent in Brazil. In contrast, Chile and Uruguay have remained fairly stable in area, while Paraguay has almost tripled its wheat area since 1981. All countries except Brazil have shown a significant increase in the growth rate of wheat yield since 1951, largely due to improved cultivars and cultural practices, and particularly improved disease resistance. Brazil did show a dramatic 7.9 percent increase in growth rate of yield during the decade 1976-1985, but the growth rates were slightly negative in most other decades since 1951. Soil degradation and erosion are problems throughout the region causing serious losses of soil and soil fertility. Conservation tillage practices, especially zero-tillage and adding green manure crops in the rotation, are spreading rapidly in the region (M.M. Kohli, personal communication, 1998).

All countries are net importers of wheat except Argentina, which exported almost 6 million tonnes annually during the period 1992-1994. Per caput consumption is 70 kg for the region, which has a population of about 220 million (CIMMYT, 1996).

Environments for wheat production in the Southern Cone are highly variable, ranging from the favourable pampa húmeda (humid plains) of Argentina to the acid soil conditions of Brazil. Wheat is grown in the tropical Cerrado area, close to Brasilia in Brazil (15°S), and as far south in Chile as 41°S, near Puerto Montt.

Environmental stresses are great in the region and include unpredictable climate, high temperature regime, low solar radiation, drought, soil problems, preharvest sprouting, diseases and insect pests. In Argentina, environmental factors affecting the crop during the growth cycle are early and late heat, early and midterm drought, frosts at flowering and rains at harvest. Diseases can limit production, but most commercial cultivars are resistant to stem, leaf and stripe rusts. Better resistance is needed against Septoria tritici blotch, scab and bacterial leaf streak (Xanthomonas translucens pv. undulosa). Nitrogen fertilizer usage in the country averages about 20 kg/ha. However, in the more moist southern areas, the average is about 40 kg/ha of nitrogen, although some farmers use 50 to 60 kg/ha.

In Brazil, yields are low and unstable due to: (i) acid soils with high levels of soluble aluminium and strong phosphorous fixation; (ii) severe disease pressures from rusts, Septoria, Helminthosporium, scab and powdery mildew; (iii) variable rainfall, often excessive in south Brazil and short in central Brazil; and (iv) unseasonable frosts. In northern Brazil, early-, mid- and late-season heat and mid- and late-season drought adversely affect the crop. Frosts at flowering and excess rain at harvest are common. In southern Brazil, frosts at flowering and rains at harvest can severely reduce production (Kohli and McMahon, 1988).

Wheat production in Chile increased dramatically during the decade 1981-1991 from 0.65 to 1.7 million tonnes. Wheat area also increased from 0.37 to 0.58 million ha. Yields made a corresponding gain from 1.7 to 3.2 tonnes/ha, largely due to greatly improved cultivars and some improvements in cultural practices. Wheat area reduced sharply during the 1993-1995 period to an average of 0.38 million ha, but yield per hectare has continued to climb. Uruguay and Paraguay are minor wheat producers in the Southern Cone. Since 1981, Uruguay wheat area (201 000 ha) has remained relatively stable, while Paraguay has almost tripled its area (202 000 ha). During this period, yields in Uruguay increased from 1.1 to 2.0 tonnes/ha and in Paraguay from 1.6 to 2.2 tonnes/ha. Diseases are the most important yield-limiting factors to wheat production in Uruguay (M.M. Kohli, personal communication, 1998).

Western Europe

The major wheat-growing countries in Western Europe in order of production are France, Germany, the United Kingdom, Italy, Spain and Portugal. Other countries with significant production are Belgium/Luxembourg, the Netherlands and Denmark. The season for growing wheat is long, generally 10 to 11 months, beginning in October or November and ending in August or early September. Winters are generally long, cloudy, cold and wet; summers are cool. The grain can be classed as SRW wheat of generally low quality due to low protein content and poor gluten content. Spring wheat is grown on less than 10 percent of the area. Although lodging remains a problem, newer cultivars with shorter and stiffer straw have greatly alleviated the problem. Western Europe is a heavy user of nitrogen, phosphorus and potassium (NPK) fertilizer.

Western European countries have the highest yields in the world, where five of the eight countries listed in Table 1.1 had aver-ages exceeding 6 tonnes/ha. The Netherlands reaped an astounding 8.6 tonnes/ha from 1993 to 1995, with the United Kingdom averaging 7.5 tonnes/ha.

Diseases, such as scab, stripe rust, Septoria tritici blotch, Septoria nodorum blotch and various root rots, cause some losses each year, particularly on continental Europe. Spraying with fungicides is commonly practised to control these diseases.

Eastern Europe and the former Soviet Union

During the 1993-1995 period, total wheat area harvested in Eastern Europe and the former Soviet Union countries averaged about 54.6 million ha annually; however, nine major producers of the 13 countries harvested an average of about 51.1 million ha or near 94 percent of the total (CIMMYT, 1996). Yields are high and vary between 2.7 tonnes/ha for Romania to a 4.4 tonnes/ha average for former Czechoslovakia. Yields in Kazakhstan were only 0.7 tonnes/ha compared with 1.5 tonnes/ha for the Russian Federation (Table 1.1).

The climate of Eastern Europe varies from oceanic to continental, with very cold and usually wet winters. The wheats grown are mostly winter-habit types and are sown in the autumn. Planting occurs during September and October, and harvest occurs in July and August. NPK fertilizers are used heavily, and in some areas calcium (Ca) and magnesium (Mg) fertilizers are also required. Pesticides are used heavily as well (CIMMYT, 1978).

Major constraints to production in Eastern Europe include diseases, lodging and winterkill of plants. Droughts also occur in some years and can result in serious crop losses. The diseases reported most often are powdery mildew, dryland root rot, scab, the three rusts, Septoria nodorum blotch and eyespot (Pseudocercosporella herpotrichoides [Fron] Deighton). Lodging causes heavy losses and is being partially reduced through use of the plant growth regulator CCC ([2-chloroethyl] trimethylammonium chloride) to reduce straw height and through using shorter- and stiffer-strawed cultivars. Much of the wheat in Eastern Europe is used as a feed grain.

Much of the agricultural area in the former Soviet Union has a similar climate to the area cultivated in Canada and the north-central states of the United States. In those wheat-growing areas that lie at the same latitudes as the Prairie Provinces of Canada, the growing season is short, and late frosts and early snows are common. Areas warm enough for better plant growth lack sufficient rainfall. Semi-desert and desert areas dominate the southern part of the region. Variability of weather from year to year has a deleterious effect on agricultural production in the area of the former Soviet Union. Yields are frequently diminished and sometimes crops are lost entirely because of drought, desiccating winds or violent storms. Water is often too limited for irrigation purposes. A major agricultural asset is the broad belt of fertile Chernozem soil (Mollisols) that extends from the western border of the Ukraine far beyond the Ural Mountains and into Kazakhstan and western Siberia. Most of the wheat produced is used for bread. The spring wheat is high in protein and has very good baking quality. The very low-quality grain is fed to livestock.

East Asia

The 29 million ha of wheat grown and 102.6 million tonnes harvested annually in China during the 1993-1995 period constitutes the largest area and production of any country in the world. Wheat is grown on 33 percent of all cereal area in China. Although there was little increase of growth rate in wheat area, the growth rate of wheat yield in China has shown an increase in every decade since 1951. The greatest gain was during the period 1977-1985 when the yield growth rate increased 8.4 percent. The growth rate of production during the same period was 8.6 percent. Yield averaged 3.5 tonnes/ha in the period 1993-1995. In spite of this, China annually imports 8.7 million tonnes to reach the 93 kg/caput consumption rate (CIMMYT, 1996).

Wheat is grown throughout China, with most east of the 100th meridian. The three main wheat-growing areas, designated according to growth habit, are the northern winter wheat region, the southern winter wheat region (where facultative and spring wheats are autumn sown) and the spring wheat region. These are further subdivided into ten subregions. The majority of the total area is sown to winter wheat. White grain is preferred, but large quantities of red grain are produced. Wheats with semidwarf stature now predominate in China.

Environmental stresses vary across the regions. Spring drought and hot dry winds during the grainfilling period of the crop are common in the northern and western wheat areas. In the central and southern wheat-growing areas, where more moisture is available, double- or triple-cropping in rice-wheat rotations is common. Excessive moisture and sprouting in the head are common problems (Q. Zhuang, personal communication, 1984).

Diseases can cause major crop losses in China. Leaf, stem and stripe rusts remain a constant source of concern throughout most of the ten wheat regions. Scab is a serious disease in the Yangtze River Valley with measurable losses occurring every year. Other important diseases in China are powdery mildew, BYDV, leaf blights, root rots, common bunt, loose smut and snow mould. Insects causing damage to the wheat crop include aphids, armyworms and various soil-inhabiting species (Z. Liu, personal communication, 1982).

The Republic of Korea produces a very small amount of wheat and imports 4.8 million tonnes annually. Consumption is 104 kg/caput. The Democratic People’s Republic of Korea produces only 124 000 tonnes of wheat annually and imports a small amount. Mongolia harvested an annual average of 343 000 tonnes of wheat from a planted area of 425 000 ha during the period 1993-1995 (Table 1.1).

South Asia

Wheat production involves a huge area in South Asia where 78 million tonnes were produced annually on 34.5 million ha during the period 1993-1995. The wheat-producing countries are India, Pakistan, Nepal, Bangladesh and Myanmar in order of importance. The greatest amount of wheat is produced in the Ganges and Nurmada basins of India and the Indus River Valley of Pakistan. Much of the wheat in India and Pakistan is irrigated, while in Nepal and Bangladesh it is mostly rainfed. White grain cultivars are preferred and are primarily of spring habit, but usually sown in November and December and harvested in April and May. All countries in South Asia are net importers of wheat. Consumption is highest in Pakistan at 141 kg/caput and lowest in Myanmar at 3 kg/caput (Table 1.1).

India is one of the largest wheat producers in the world with about 25 million ha under production and averaging almost 60 million tonnes in recent years. More than 90 percent of the area is sown to bread wheat, which is grown throughout the country. Durum or macaroni wheat accounts for around 8 percent of the area. The crop is grown in most parts of the country, but nearly 70 percent lies in the northern plains and 20 percent in central India. India has achieved remarkable progress in increasing wheat production and productivity. Over the 1967-1990 period, wheat area expanded at an annual rate of 2.5 percent, production by 5.2 percent and productivity (tonnes/ha) by 3.1 percent (Tandon, 1993).

High-yielding, semidwarf cultivars from Mexico were introduced into India in 1962 when the average annual production for the country was about 11 million tonnes. With their resistance to lodging and improved disease resistance, these introduced cultivars took advantage of improved cultural practices, including heavier fertilizer application. In succeeding years, production increased as the semidwarf cultivars were further improved for disease resistance, productivity and response to more intensive cropping systems. Irrigated wheat is grown in a system where cropping intensity is 200 percent or more. A rice-wheat rotation is the dominant cropping sequence. Crops other than rice that precede wheat are also used, particularly in the central and southern regions. In the large wheat research and development programme in India, much germplasm is screened for important biotic and abiotic stresses. Important biotic pests include the rusts, Karnal bunt, foliar blight, powdery mildew, common bunt, flag smut and nematode and insect pests. Salt, heat and drought are the major abiotic stresses. Large amounts of NPK fertilizers are used to produce the wheat crop in India (Tandon, 1993).

Over the past three decades, increased agricultural productivity in Pakistan occurred largely due to the deployment of high-yielding cultivars, increased fertilizer use and greater availability of irrigation water. By the mid-1980s, semidwarf wheat cultivars had been adopted on almost all irrigated land, and over 100 kg/ha on average of fertilizer was being applied to wheat. Pakistan production aver-aged 16.1 million tonnes on 8.2 million ha each year during the period 1993-1995 (Table 1.1). Rice-wheat, berseem-wheat and cotton-wheat are major systems of intense cropping in Pakistan (Aslam et al., 1989).

Nepal has shared similar results of improved wheat production as those for Pakistan and northern India and for essentially the same reasons. Wheat production figures for Bangladesh increased dramatically from 1966 to 1985. At that time, wheat was grown on 126 000 ha with an average yield of 1 tonne/ha. Wheat area increased to more than 600 000 ha by 1985 with a 2.16 tonnes/ha yield. However, wheat area, production and yield decreased slightly during the period 1985-1995.

West Asia

Five countries, Turkey, Iran, Iraq, Syria and Afghanistan, produce about 95 percent of the wheat in West Asia, with the wheat area of Turkey and Iran comprising 75 percent of the total area and production. Yield levels vary from 0.7 tonnes/ha in Iraq to 4.5 tonnes/ha on the irrigated lands of Saudi Arabia. Turkey and Iran yields are below 2.0 tonnes/ha. Turkey and Saudi Arabia are net exporters while all other countries of the region are net importers. During the period 1992-1994, consumption for the region averaged 203 kg/caput with Turkey consuming 304 kg/caput (CIMMYT, 1996). Consumption is in many forms, such as leavened and unleavened breads and bulgar.

Climatic conditions for the region are variable and diverse. There are two major agro-climatic zones where cereals are grown, Mediterranean and highland. The Mediterranean zone is characterized by hot, dry summers and cool, moist winters. Rainfall is highly erratic, causing substantial fluctuations in crop productivity. In the high-land zone, much of which exceeds 1 000 m in elevation, winters are cold and summers hot. With the notable exception of Turkey, the soils in this zone are generally shallow. Crops are usually planted in the autumn, although spring plantings are important in parts of Turkey and Afghanistan.

The major constraints affecting crop production are drought, diseases, insects and weeds. Rainfall is received in variable amounts on the arable land, ranging from only 200 to 600 mm/year; distribution is highly variable as well. Little irrigation is practised.

Major diseases are leaf, stripe and stem rusts, Septoria tritici blotch, powdery mildew, common and dwarf bunts, loose smut, tan spot and BYDV. Hessian fly and wheat stem sawfly cause significant losses in some years. Sunn pest and aphids are other insects of importance (Miller, 1991).

Two classes of wheat, common and durum, are the major crops. Common wheat is the most prevalent, particularly in the higher rainfall areas. Durum wheat occupies a large area, but is primarily grown where rainfall is more limited (300 to 500 mm). Springhabit wheats predominate in the Mediterranean zone and are generally planted in the autumn. Facultative and winter wheats are more often grown in the highland zones, being planted in October and November and harvested in June and July. In recent years, research has shown that deficiencies of minor elements, such as zinc, contribute significantly to low yields. On-going research is underway to better understand the complexities of the relationship between yield and soil minor elements.

North Africa

The five countries of North Africa, Algeria, Egypt, Libya, Morocco and Tunisia, are heavy users of wheat with a regional average consumption of 215.8 kg/caput. During the period 1993-1995, the average production for the region was 8.8 million tonnes, and wheat imports averaged 14.6 million tonnes (116 kg/caput) or about 150 percent of production. Wheat is grown on about 5.5 million ha of which most is rainfed except in Egypt where nearly all wheat is irrigated. Yields under rainfed conditions average near 1 tonne/ha, while yields exceed 5 tonnes/ha under irrigation in Egypt (Table 1.1).

The total cereal-growing area of North Africa is about 50 percent durum wheat and 20 percent common wheat, with barley occupying most of the remaining area. Rainfall is highly variable in amount and distribution and occurs in the winter months. Wheat is grown as a winter crop to coincide with the rainy season. Harvest is in May or June.

Major hazards of wheat production, in addition to a lack of moisture, include diseases, insects and a lack of adoption of improved cultural practices. Septoria tritici blotch and stripe rust can cause severe losses in the wetter years. Other prevalent diseases include stem rust, powdery mildew, tan spot and root rots. Hessian fly annually causes major damage, particularly in Morocco, as does wheat stem sawfly in several countries. Aphids and nematodes also cause problems in some years.

East and Southern Africa

Wheat grown in South Africa, Ethiopia, Sudan and Kenya on 2.5 million ha makes up 94 percent of the total area planted to wheat in East and Southern Africa. Tanzania, Zimbabwe and Zambia collectively plant 105 000 ha, with a minor amount being grown in Angola, Mozambique and Somalia. Wheat production in the region has averaged 4.3 million tonnes annually in recent years and 2.8 million tonnes were imported; all countries are net importers. Consumption varies from 61 kg/caput in South Africa to 5 kg/caput in Tanzania. Yield average for the region in the 1993-1995 period was 1.6 tonnes/ha, with high yields of 4.9 tonnes/ha for Zimbabwe and 3.1 tonnes/ha for Zambia and a very low yield of 0.4 tonnes/ha for Somalia (CIMMYT, 1996).

Most of the wheat in East Africa is grown at high elevations (above 1 500 m). Along the equator, the elevation for wheat is 3 000 m or more. Wheat is generally produced under rainfed conditions, except in the lowlands of Somalia, Zambia and Zimbabwe where irrigation is practised. In the highlands, the average rainfall is between 600 and 700 mm and usually falls from June to September. Soils are generally low in nitrogen (N) and phosphorus (P) and some minor elements. Wheat is usually planted from May to July and harvested in September or October. In Kenya, a second crop is sometimes grown. Common wheat is grown in much of East Africa, except in Ethiopia where durum wheat is grown on 60 to 70 percent of the area.

The major diseases in the highlands are stripe rust and Septoria blotches, particularly Septoria tritici blotch. Stem rust can be very damaging to common wheat in Kenya and durum wheat in Ethiopia. Other diseases important in some years are common bunt, loose smut, BYDV and bacterial leaf streak.

In South Africa, during the 1993-1995 period wheat was grown annually on about 1.2 million ha with a production average of nearly 2.0 million tonnes. Average yield was 1.7 tonnes/ha. Low yields result from low rainfall in the Transvaal, the winter wheat area, and from poor soils in areas of heavier rainfall. Stem rust is the most important disease of winter wheat and when associated with root rots, under favourable conditions for the pathogens, can reduce yield by as much as 50 percent. Leaf rust and Septoria tritici blotch are common but generally not overly destructive to yield. Aphids can cause severe damage in some years. Planting occurs from April to August and September, except in the northern Transvaal where planting is from February to March and harvest occurs in July. The rest of the crop is harvested from November to January. Wheat is used for human consumption in the form of bread, cakes, pastries and cookies.

Oceania

Australia grew wheat on an average of 8.7 million ha during the 1993-1995 period with an average production of about 14.0 mil-lion tonnes of which nearly 73 percent was exported (Table 1.1). Area planted to wheat has varied as much as 25 percent from a high exceeding 12.2 million ha to a low of about 8.5 million ha during the years from 1982 through 1995. Yields in tonnes per hectare have gradually increased during the same period. Most wheat is grown in the arcuate belt of land curving across the eastern and southern regions where winter rainfall is sufficient to produce a crop. Spring wheat is grown as a winter crop sown in the autumn (May to June) and harvested in early summer (November to December).

Wheat yields in Australia are low and highly variable primarily due to extreme fluctuations in annual rainfall, which varies from 250 to 650 mm from May through October. Other constraints to production are low soil fertility, diseases (stem rust, stripe rust, Septoria blotches and take-all) and nematodes. Application of N (through pasture farming methods) and P give good crop responses. The amount of total wheat area devoted to semidwarf cultivars was 91 percent in 1994 (CIMMYT, 1996).

Wheat is a major crop in New Zealand but is grown on only 39 000 ha, with production averaging 232 000 tonnes during the 1993-1995 period. Production area is primarily on the eastern side of the South Island. Yields are high with a national average of 6.0 tonnes/ha. Both winter- and spring-habit wheats are grown.

WHEAT PRODUCTION IN THE FUTURE

The world population growth rate from 1993 to 2000 is estimated at 1.5 percent, while the growth rate of wheat production from 1985 to 1995 was 0.9 percent (CIMMYT, 1996). If population growth continues to double the growth of wheat production, there will likely be serious difficulties in maintaining a wheat food supply for future generations. World population was projected to be 5.8 billion people at the end of 1997 and is expected to reach 7.9 billion by the year 2025, or roughly a 35 percent increase (United States Census Bureau, 1998). In simplistic terms and assuming little or no change in world per caput consumption of wheat, a projection of 786 million tonnes of wheat will be required annually for human use in the year 2025, an annual production increase of 204 million tonnes above production in 1997. This underscores the need to rapidly and continuously increase production. Greater wheat production can be achieved in two ways: (i) by expanding the wheat area; and (ii) by improving the yield per unit area sown. In addition, reducing pre- and post-harvest losses would make more wheat available for consumption.

Area expansion

Due to other agricultural and non-agricultural uses, an increased area of productive agricultural lands is not likely to be available for wheat production. Thus, any increased land area for wheat will, of necessity, come from the use of more marginal or non-traditional areas. Improved cultivars and cultural techniques have been under development by plant breeders and agronomists for several years to allow wheat to be grown under more adverse conditions, such as in acid and saline soils, with greater heat tolerance and in more tropical environments. Considerable progress has been achieved toward these improvements, but further research will be necessary to ensure stable wheat production under the more difficult environments required for area expansion.

Social and economic incentives that encourage farmers to adopt progressive agricultural technologies are also necessary. Since most potential farmers in non-traditional areas operate at a subsistence level, new agricultural technologies must be profitable. In most countries, the establishment of government programmes to facilitate adequate distribution of inputs to farmers and delivery of their increased production to the market will be necessary.

Yield improvement

Crop yields are dependent on interactions of socio-economical, biological, technological and ecological factors. Considerable controversy exists among scientists regarding the achievements that can be made to further increase wheat yield per unit of area. A large gap exists between yields that have been accomplished in experimental fields versus those attained in farmers’ fields. The absolute yield, based on genetic potential, is projected to be 20 tonnes/ha (Hanson et al., 1982). The highest commercial attainable yield reported is 14 tonnes/ha under a given environment, location and year (Cook and Veseth, 1992). In contrast, the wheat yield average for the world during the period 1993-1995 was 2.5 tonnes/ha. Closing the yield gap must, of necessity, be one of the major goals of organizations involved with world food policy and wheat research for the future.

Current research to improve wheat yields covers a broad front and includes further mixing of germplasm through crossing, interspecific and intergeneric hybridization, biotechnology techniques, hybrid wheat, basic studies on the physiology of the wheat plant and on the host-plant relationships of various pests that attack it and numerous other important research avenues.

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