Wheat in the world - B.C. Curtis (2024)

The cultivation of wheat (Triticum spp.) reaches farback into history. Wheat was one of the first domesticated food crops and for 8000 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 anyother commercial crop and continues to be the most important food grain sourcefor humans. Its production leads all crops, including rice, maize andpotatoes.

Although the crop is most successful between the latitudes of30° and 60°N and 27° and 40°S (Nuttonson, 1955), wheat canbe grown beyond these limits, from within the Arctic Circle to higher elevationsnear the equator. Development research by the International Maize and WheatImprovement Center (CIMMYT) during the past two decades (Saunders and Hettel,1994) has shown that wheat production in much warmer areas is technologicallyfeasible. 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, withminimum and maximum growth temperatures of 3° to 4°C and 30° to32°C, respectively (Briggle, 1980). Wheat is adapted to a broad range ofmoisture conditions from xerophytic to littoral. Although about three-fourths ofthe land area where wheat is grown receives an average of between 375 and 875 mmof annual precipitation, it can be grown in most locations where precipitationranges from 250 to 1 750 mm (Leonard and Martin, 1963). Optimal productionrequires an adequate source of moisture availability during the growing season;however, too much precipitation can lead to yield losses from disease and rootproblems. Cultivars of widely differing pedigree are grown under variedconditions of soil and climate and show wide trait variations. Although wheat isbeing harvested somewhere in the world in any given month, harvest in thetemperate zones occurs between April and September in the Northern Hemisphereand between October and January in the Southern Hemisphere (Percival,1921).

Classification into spring or winter wheat is common andtraditionally refers to the season during which the crop is grown. For winterwheat, heading is delayed until the plant experiences a period of cold wintertemperatures (0° to 5°C). It is planted in the autumn to germinate anddevelop into young plants that remain in the vegetative phase during the winterand resume growth in early spring. This provides the advantage of using autumnmoisture for germination and making effective use of early spring sunshine,warmth and rainfall. Spring wheat, as the name implies, is usually planted inthe spring and matures in late summer but can be sown in autumn in countriesthat experience mild winters, such as in South Asia, North Africa, the MiddleEast and the lower latitudes.

Wheat is special in several ways. Wheat is grown on more than240 million ha, larger than for any other crop, and world trade is greater thanfor all other crops combined. The raised bread loaf is possible because thewheat kernel contains gluten, an elastic form of protein that traps minutebubbles of carbon dioxide when fermentation occurs in leavened dough, causingthe dough to rise (Hanson et al., 1982). It is the best of the cerealfoods and provides more nourishment for humans than any other food source. Wheatis a major diet component because of the wheat plant’s agronomicadaptability, ease of grain storage and ease of converting grain into flour formaking edible, palatable, interesting and satisfying foods. Doughs produced frombread wheat flour differ from those made from other cereals in their uniqueviscoelastic properties (Orth and Shellenberger, 1988). Wheat is the mostimportant source of carbohydrate in a majority of countries. Wheat starch iseasily digested, as is most wheat protein. Wheat contains minerals, vitamins andfats (lipids), and with a small amount of animal or legume protein added ishighly nutritious. A predominately wheat-based diet is higher in fibre than ameat-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 inyears where harvests are adversely affected by rain and significant quantitiesof the grain are made unsuitable for food use. Such low-grade grain is oftenused by industry to make adhesives, paper additives, several other products andeven in the production of alcohol.

PRODUCTION AND TRADE

World wheat production increased dramatically during theperiod 1951-1990, although the expansion of the area sown to wheat has longceased to be a major source of increased wheat output (CIMMYT, 1996) (Figure1.1). Production reached an all time high of 592 million tonnes in 1990 and hasbeen 500 million tonnes or above since 1986 when 529 million tonnes wasproduced. Since 1990, production has remained relatively constant. The share ofwheat output from high-income countries has fallen from about 45 percent in theearly 1950s to about 35 percent in recent years. Policy changes toward cropreserve programmes to preserve soils have taken considerable production areafrom wheat in high-income countries. In the past five years, developingcountries have produced more than 45 percent of the world’swheat.

Figure 1.2
Wheat yields worldwide, 1951-1995

Source: CIMMYT, 1996.

Most of the increase in world wheat production resulted fromgreater yield per hectare (Figure 1.2). In 1951, world production was nearly 1tonne/ha. It reached 2 tonnes/ha by the early 1980s and climbed to nearly 2.5tonnes/ha by 1995. Yields have world2Bread wheat: improvementand production33 continued to climb with little suggestion of a trendreduction. Both genetically improved cultivars for yield and better culturalmethods have contributed to the yield increases, but it is difficult to quantifythe effects of each. Yield stability has increased substantially acrossenvironments largely due to the adoption of management-responsive,high-yielding, disease-resistant semidwarf wheat cultivars (usually referred asHYVs) throughout much of the world, particularly in developing countries.Improved agronomic practices also played an important role in enhancing thedependability and sustainability of yields. In Turkey, for example, productionnearly doubled from 9 to about 17.5 million tonnes between 1971 and 1982. Thisimpressive increase resulted primarily from the use of water-conserving culturalpractices on the Anatolian Plateau (Curtis, 1982; Dalrymple, 1986). The use ofproduction inputs, primarily nitrogen fertilizer and irrigation water, has risendramatically. India and China are two major wheat-producing countries wherethese inputs have dramatically increased. In China, the yield of all cerealsincreased from 1.4 to 4.6 tonnes/ha from 1961 through 1995, and during the sameperiod, 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-producingcountries of the world, along with information on average area, yield,production, net imports and consumption during the period 1993-1995. China hasthe largest land area devoted to wheat production, followed closely by theUnited States, India and the Russian Federation. Kazakhstan and Canada, rankingfifth 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 milliontonnes annually ranks far ahead of the United States and India, each averagingnear 60 million tonnes. Production increases in China have been dramatic inrecent years; production in 1995 was 3 percent higher than in 1994.

Among the larger land area producers, China's yield was 3.5tonnes/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 isproduced, roughly one-fifth of the annual crop is exported. World wheat tradewas estimated at 108 million tonnes in 1995, most of which was imported bydeveloping countries. Despite increase in production during the past threedecades, developing countries account for two-thirds of all wheat imports, whichis up from less than half in 1961. China, the world’s largest wheatproducer, is also the world’s largest wheat importer, averaging more than10 million tonnes annually since 1980 (CIMMYT, 1996). Other countries importingmore than 5 million tonnes annually include the Russian Federation, Egypt, Japanand Brazil.

The United States, Canada, France and Australia continue to bethe largest exporting countries, ranging from 32.7 to 10.2 million tonnes,respectively. Except for France, the wheat imported from these high-incomecountries is usually a quality product purchased to supplement and enhance theuse-potential of locally grown wheat. Canada is considered an important sourceof high-quality, high-protein wheat for importing countries. The United Statesproduces a wide range of hard and soft wheat possessing grain protein rangingfrom 7 to 8 percent in soft wheat to 19 to 20 percent in hard wheats (Johnsonet 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 tonnessince 1990. Consumption worldwide has increased rapidly since the early 1960s.Wheat consumption in developing countries rose 35 percent during the period1963-1976. This primarily resulted from increased urbanization and an associatedshift in tastes and preferences to wheat over rice and coarse grains, such asmaize and sorghum. Also important was the increased adoption of wheat as a foodin countries that had consumed little wheat in the past. The influence ofurbanization on wheat consumption was most clearly seen in sub-Saharan Africawhere per caput consumption growth rates in the late 1970s and early 1980sexceeded 6 percent annually. Annual consumption growth rates in those areas havenow decelerated to near zero or less, while average per caput consumptionremains near 10 kg/year. Urban consumers tend to prefer convenience-type foodsthat require little or no preparation (Curtis, 1982). From the mid-1980s to thepresent, the annual growth of wheat consumption in all developing countries hasdecelerated from about 5 percent to less than 2 percent. In high-incomecountries with mature food wheat markets, changes in consumption take placeslowly over time and are driven by population growth and changing dietarypreferences (CIMMYT, 1996).

WHEAT AROUND THE WORLD

North America

United States

Wheat area, production and yield levels in the United Stateshave remained relatively stable during the past 40 or more years, with wheatprices reflecting most changes in area. Growth rate in wheat yield and in rateof production continues a slow but steady increase, characteristic of a maturemarket. Five classes of wheat are grown (Table 1.2) in four regions. Most USwheat is grown in the Great Plains from Texas to North Dakota. The area of wheatproduction during the period 1993-1995 (Table 1.1) was about 25 million ha, withan annual production averaging 62.6 million tonnes. Average yield for the periodwas 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 (Table1.2). 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 allSRW wheat is grown in the east. White wheat is grown primarily in the PacificNorthwest 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 recentinterest 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 ofthe Prairie Provinces of Manitoba, Saskatchewan and Alberta produce about 95percent 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 importantfactor 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 countriesneeding to improve the baking properties of their flour products.

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

Canada exported an average of 84 percent of its wheat in theperiod 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 thisregion are Mexico and Guatemala. During the period 1993-1995, Mexico harvested930 000 ha/year, while Guatemala harvested 23 000 ha. Area harvested in Mexicogrew at the rate of 1.9 percent/year from 1948 to 1985, but the area declined bya total of 2.4 percent during the decade 1986-1995. Rate of growth in wheatproduction from 1951 to 1985 had a steady increase of 6.2 percent, but sincethen the growth rate has declined by 2.6 percent. The growth rate of tonnes perhectare 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 theintroduction of high-yielding, semi-dwarf and disease-resistant wheats duringthe early 1960s (Dalrymple, 1986). Per caput consumption has been near 55kg/caput since 1951. The increase of population from 73.9 to 93.7 million peoplefrom 1982 to 1995 has necessitated increased net imports averaging 1 427 milliontonnes in the period 1992-1994.

Wheat makes up about 10 percent of the total cereal area inMexico 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 thestates of Sonora and Sinaloa. The Bahia region of the central plateau producesabout 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 onsusceptible cultivars as young plants. Use of resistant cultivars has beenfairly successful in control of the rusts, particularly with stem rust. Leafrust is highly heterogeneous, and more difficulty is encountered in maintaininggenetic resistance through breeding. Stripe rust (P. striiformis),Septoria nodorum blotch and Septoria tritici blotch (Leptosphaeria nodorumand Mycosphaerella graminicola), barley yellow dwarf virus (BYDV) andscab (Fusarium spp.) are often a problem in the highlands (Briggle andCurtis, 1987).

In Guatemala, wheat is produced in highland valleys underrainfed conditions, and yields average about 1.1 tonnes/ha (Table 1.1). Diseasesadversely affect the crop under the usually wet production conditions. Thesediseases 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 ofBolivia, Peru, Colombia, Ecuador and Venezuela was only about 355 000 tonnes on301 000 ha during the 1993-1995 period. Yields ranged from 0.3 tonnes/ha inVenezuela to 2.0 tonnes/ha in Colombia. Average per caput consumption during theperiod 1992-1994 for the region was 45 kg/year, ranging from 26 kg in Ecuador to73 kg in Bolivia. With a 101.1 million population, the region imported anaverage of 37.5 million tonnes or about 42 kg/caput from 1992 to 1994. In spiteof government intervention attempts to increase wheat area and production in theregion in recent years, only marginal gains of 1 to 2 percent have been made forthese objectives since 1985.

Production constraints are moisture availability, diseases,poor cultural practices and a general lack of necessary inputs, such asfertilizers, pesticides and farm implements. Rainfall is highly variable fromyear to year in both amount and distribution. Much improved cultivars have beendeveloped for the region, but seed availability and distribution continues to bea problem for most areas. Improved cultural techniques have been developed forsome areas, but the technology transfer to producers has been minimal due tolimited budgets and consequent lack of infrastructure to utilize trainedtechnicians.

Southern Cone region

Between 7 and 10 million ha of wheat are grown in the largeSouthern 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 andBrazil’s was 1.5 tonnes/ha. Wheat area in both countries has been reducedsince 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 almosttripled its wheat area since 1981. All countries except Brazil have shown asignificant increase in the growth rate of wheat yield since 1951, largely dueto improved cultivars and cultural practices, and particularly improveddisease resistance. Brazil did show a dramatic 7.9 percent increase in growthrate of yield during the decade 1976-1985, but the growth rates were slightlynegative in most other decades since 1951. Soil degradation and erosion areproblems throughout the region causing serious losses of soil and soilfertility. Conservation tillage practices, especially zero-tillage and addinggreen 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. Percaput consumption is 70 kg for the region, which has a population of about 220million (CIMMYT, 1996).

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

Environmental stresses are great in the region and includeunpredictable 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 andlate heat, early and midterm drought, frosts at flowering and rains at harvest.Diseases can limit production, but most commercial cultivars are resistant tostem, leaf and stripe rusts. Better resistance is needed against Septoriatritici blotch, scab and bacterial leaf streak (Xanthom*onas translucenspv. undulosa). Nitrogen fertilizer usage in the country averagesabout 20 kg/ha. However, in the more moist southern areas, the average is about40 kg/ha of nitrogen, although some farmers use 50 to 60 kg/ha.

In Brazil, yields are low and unstable due to: (i) acid soilswith 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 southBrazil and short in central Brazil; and (iv) unseasonable frosts. In northernBrazil, early-, mid- and late-season heat and mid- and late-season droughtadversely affect the crop. Frosts at flowering and excess rain at harvest arecommon. In southern Brazil, frosts at flowering and rains at harvest canseverely reduce production (Kohli and McMahon, 1988).

Wheat production in Chile increased dramatically during thedecade 1981-1991 from 0.65 to 1.7 million tonnes. Wheat area also increased from0.37 to 0.58 million ha. Yields made a corresponding gain from 1.7 to 3.2tonnes/ha, largely due to greatly improved cultivars and some improvements incultural practices. Wheat area reduced sharply during the 1993-1995 period to anaverage 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 Paraguayhas almost tripled its area (202 000 ha). During this period, yields in Uruguayincreased 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 inUruguay (M.M. Kohli, personal communication, 1998).

Western Europe

The major wheat-growing countries in Western Europe in orderof production are France, Germany, the United Kingdom, Italy, Spain andPortugal. Other countries with significant production are Belgium/Luxembourg,the Netherlands and Denmark. The season for growing wheat is long, generally 10to 11 months, beginning in October or November and ending in August or earlySeptember. 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 lowprotein content and poor gluten content. Spring wheat is grown on less than 10percent of the area. Although lodging remains a problem, newer cultivars withshorter and stiffer straw have greatly alleviated the problem. Western Europe isa heavy user of nitrogen, phosphorus and potassium (NPK) fertilizer.

Western European countries have the highest yields in theworld, where five of the eight countries listed in Table 1.1 had aver-agesexceeding 6 tonnes/ha. The Netherlands reaped an astounding 8.6 tonnes/ha from1993 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 commonlypractised to control these diseases.

Eastern Europe and the former Soviet Union

During the 1993-1995 period, total wheat area harvested inEastern Europe and the former Soviet Union countries averaged about 54.6 millionha annually; however, nine major producers of the 13 countries harvested anaverage 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/haaverage for former Czechoslovakia. Yields in Kazakhstan were only 0.7 tonnes/hacompared with 1.5 tonnes/ha for the Russian Federation (Table 1.1).

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

Major constraints to production in Eastern Europe includediseases, lodging and winterkill of plants. Droughts also occur in some yearsand can result in serious crop losses. The diseases reported most often arepowdery mildew, dryland root rot, scab, the three rusts, Septoria nodorum blotchand eyespot (Pseudocercosporella herpotrichoides [Fron] Deighton).Lodging causes heavy losses and is being partially reduced through use of theplant growth regulator CCC ([2-chloroethyl] trimethylammonium chloride) toreduce 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 asimilar climate to the area cultivated in Canada and the north-central states ofthe United States. In those wheat-growing areas that lie at the same latitudesas the Prairie Provinces of Canada, the growing season is short, and late frostsand early snows are common. Areas warm enough for better plant growth lacksufficient rainfall. Semi-desert and desert areas dominate the southern part ofthe region. Variability of weather from year to year has a deleterious effect onagricultural production in the area of the former Soviet Union. Yields arefrequently diminished and sometimes crops are lost entirely because of drought,desiccating winds or violent storms. Water is often too limited for irrigationpurposes. A major agricultural asset is the broad belt of fertile Chernozem soil(Mollisols) that extends from the western border of the Ukraine far beyond theUral Mountains and into Kazakhstan and western Siberia. Most of the wheatproduced is used for bread. The spring wheat is high in protein and has verygood baking quality. The very low-quality grain is fed to livestock.

East Asia

The 29 million ha of wheat grown and 102.6 million tonnesharvested annually in China during the 1993-1995 period constitutes the largestarea and production of any country in the world. Wheat is grown on 33 percentof all cereal area in China. Although there was little increase of growthrate in wheat area, the growth rate of wheat yield in China has shown anincrease in every decade since 1951. The greatest gain was during the period1977-1985 when the yield growth rate increased 8.4 percent. The growth rate ofproduction during the same period was 8.6 percent. Yield averaged 3.5 tonnes/hain the period 1993-1995. In spite of this, China annually imports 8.7 milliontonnes to reach the 93 kg/caput consumption rate (CIMMYT, 1996).

Wheat is grown throughout China, with most east of the 100thmeridian. The three main wheat-growing areas, designated according to growthhabit, are the northern winter wheat region, the southern winter wheat region(where facultative and spring wheats are autumn sown) and the spring wheatregion. These are further subdivided into ten subregions. The majority of thetotal area is sown to winter wheat. White grain is preferred, but largequantities of red grain are produced. Wheats with semidwarf stature nowpredominate in China.

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

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

The Republic of Korea produces a very small amount of wheatand imports 4.8 million tonnes annually. Consumption is 104 kg/caput. TheDemocratic People’s Republic of Korea produces only 124 000 tonnes of wheatannually and imports a small amount. Mongolia harvested an annual average of 343000 tonnes of wheat from a planted area of 425 000 ha during the period1993-1995 (Table 1.1).

South Asia

Wheat production involves a huge area in South Asia where 78million tonnes were produced annually on 34.5 million ha during the period1993-1995. The wheat-producing countries are India, Pakistan, Nepal, Bangladeshand Myanmar in order of importance. The greatest amount of wheat is produced inthe 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 andBangladesh it is mostly rainfed. White grain cultivars are preferred and areprimarily of spring habit, but usually sown in November and December andharvested in April and May. All countries in South Asia are net importers ofwheat. Consumption is highest in Pakistan at 141 kg/caput and lowest in Myanmarat 3 kg/caput (Table 1.1).

India is one of the largest wheat producers in the world withabout 25 million ha under production and averaging almost 60 million tonnes inrecent years. More than 90 percent of the area is sown to bread wheat, which isgrown throughout the country. Durum or macaroni wheat accounts for around 8percent of the area. The crop is grown in most parts of the country, but nearly70 percent lies in the northern plains and 20 percent in central India. Indiahas achieved remarkable progress in increasing wheat production andproductivity. Over the 1967-1990 period, wheat area expanded at an annual rateof 2.5 percent, production by 5.2 percent and productivity (tonnes/ha) by 3.1percent (Tandon, 1993).

High-yielding, semidwarf cultivars from Mexico were introducedinto India in 1962 when the average annual production for the country was about11 million tonnes. With their resistance to lodging and improved diseaseresistance, these introduced cultivars took advantage of improved culturalpractices, including heavier fertilizer application. In succeeding years,production increased as the semidwarf cultivars were further improved fordisease resistance, productivity and response to more intensive croppingsystems. Irrigated wheat is grown in a system where cropping intensity is 200percent or more. A rice-wheat rotation is the dominant cropping sequence. Cropsother than rice that precede wheat are also used, particularly in the centraland southern regions. In the large wheat research and development programme inIndia, much germplasm is screened for important biotic and abiotic stresses.Important biotic pests include the rusts, Karnal bunt, foliar blight, powderymildew, common bunt, flag smut and nematode and insect pests. Salt, heat anddrought are the major abiotic stresses. Large amounts of NPK fertilizers areused to produce the wheat crop in India (Tandon, 1993).

Over the past three decades, increased agriculturalproductivity in Pakistan occurred largely due to the deployment of high-yieldingcultivars, increased fertilizer use and greater availability of irrigationwater. By the mid-1980s, semidwarf wheat cultivars had been adopted on almostall irrigated land, and over 100 kg/ha on average of fertilizer was beingapplied to wheat. Pakistan production aver-aged 16.1 million tonnes on 8.2million 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 productionas those for Pakistan and northern India and for essentially the same reasons.Wheat production figures for Bangladesh increased dramatically from 1966 to1985. At that time, wheat was grown on 126 000 ha with an average yield of 1tonne/ha. Wheat area increased to more than 600 000 ha by 1985 with a 2.16tonnes/ha yield. However, wheat area, production and yield decreased slightlyduring 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 ofTurkey and Iran comprising 75 percent of the total area and production. Yieldlevels vary from 0.7 tonnes/ha in Iraq to 4.5 tonnes/ha on the irrigated landsof Saudi Arabia. Turkey and Iran yields are below 2.0 tonnes/ha. Turkey andSaudi Arabia are net exporters while all other countries of the region are netimporters. During the period 1992-1994, consumption for the region averaged 203kg/caput with Turkey consuming 304 kg/caput (CIMMYT, 1996). Consumption is inmany 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, Mediterraneanand highland. The Mediterranean zone is characterized by hot, dry summers andcool, moist winters. Rainfall is highly erratic, causing substantialfluctuations in crop productivity. In the high-land zone, much of which exceeds1 000 m in elevation, winters are cold and summers hot. With the notableexception of Turkey, the soils in this zone are generally shallow. Crops areusually planted in the autumn, although spring plantings are important in partsof Turkey and Afghanistan.

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

Major diseases are leaf, stripe and stem rusts, Septoriatritici blotch, powdery mildew, common and dwarf bunts, loose smut, tan spot andBYDV. 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 morelimited (300 to 500 mm). Springhabit wheats predominate in the Mediterraneanzone and are generally planted in the autumn. Facultative and winter wheats aremore often grown in the highland zones, being planted in October and Novemberand harvested in June and July. In recent years, research has shown thatdeficiencies of minor elements, such as zinc, contribute significantly to lowyields. On-going research is underway to better understand the complexities ofthe 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 averageconsumption of 215.8 kg/caput. During the period 1993-1995, the averageproduction for the region was 8.8 million tonnes, and wheat imports averaged14.6 million tonnes (116 kg/caput) or about 150 percent of production. Wheat isgrown on about 5.5 million ha of which most is rainfed except in Egypt wherenearly all wheat is irrigated. Yields under rainfed conditions average near 1tonne/ha, while yields exceed 5 tonnes/ha under irrigation in Egypt (Table1.1).

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

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

East and Southern Africa

Wheat grown in South Africa, Ethiopia, Sudan and Kenya on 2.5million ha makes up 94 percent of the total area planted to wheat in East andSouthern Africa. Tanzania, Zimbabwe and Zambia collectively plant 105 000 ha,with a minor amount being grown in Angola, Mozambique and Somalia. Wheatproduction in the region has averaged 4.3 million tonnes annually in recentyears 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, withhigh yields of 4.9 tonnes/ha for Zimbabwe and 3.1 tonnes/ha for Zambia and avery 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 ofSomalia, Zambia and Zimbabwe where irrigation is practised. In the highlands,the average rainfall is between 600 and 700 mm and usually falls from June toSeptember. Soils are generally low in nitrogen (N) and phosphorus (P) and someminor elements. Wheat is usually planted from May to July and harvested inSeptember or October. In Kenya, a second crop is sometimes grown. Common wheatis grown in much of East Africa, except in Ethiopia where durum wheat is grownon 60 to 70 percent of the area.

The major diseases in the highlands are stripe rust andSeptoria blotches, particularly Septoria tritici blotch. Stem rust can be verydamaging to common wheat in Kenya and durum wheat in Ethiopia. Other diseasesimportant in some years are common bunt, loose smut, BYDV and bacterial leafstreak.

In South Africa, during the 1993-1995 period wheat was grownannually on about 1.2 million ha with a production average of nearly 2.0 milliontonnes. Average yield was 1.7 tonnes/ha. Low yields result from low rainfall inthe Transvaal, the winter wheat area, and from poor soils in areas of heavierrainfall. Stem rust is the most important disease of winter wheat and whenassociated with root rots, under favourable conditions for the pathogens, canreduce yield by as much as 50 percent. Leaf rust and Septoria tritici blotch arecommon but generally not overly destructive to yield. Aphids can cause severedamage in some years. Planting occurs from April to August and September, exceptin the northern Transvaal where planting is from February to March and harvestoccurs 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 andcookies.

Oceania

Australia grew wheat on an average of 8.7 million ha duringthe 1993-1995 period with an average production of about 14.0 mil-lion tonnes ofwhich nearly 73 percent was exported (Table 1.1). Area planted to wheat hasvaried as much as 25 percent from a high exceeding 12.2 million ha to a low ofabout 8.5 million ha during the years from 1982 through 1995. Yields in tonnesper hectare have gradually increased during the same period. Most wheat is grownin the arcuate belt of land curving across the eastern and southern regionswhere winter rainfall is sufficient to produce a crop. Spring wheat is grown asa 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 variableprimarily due to extreme fluctuations in annual rainfall, which varies from 250to 650 mm from May through October. Other constraints to production are low soilfertility, diseases (stem rust, stripe rust, Septoria blotches and take-all) andnematodes. Application of N (through pasture farming methods) and P give goodcrop responses. The amount of total wheat area devoted to semidwarf cultivarswas 91 percent in 1994 (CIMMYT, 1996).

Wheat is a major crop in New Zealand but is grown on only 39000 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 arehigh with a national average of 6.0 tonnes/ha. Both winter- and spring-habitwheats are grown.

WHEAT PRODUCTION IN THE FUTURE

The world population growth rate from 1993 to 2000 isestimated at 1.5 percent, while the growth rate of wheat production from 1985 to1995 was 0.9 percent (CIMMYT, 1996). If population growth continues to doublethe growth of wheat production, there will likely be serious difficulties inmaintaining a wheat food supply for future generations. World population wasprojected to be 5.8 billion people at the end of 1997 and is expected to reach7.9 billion by the year 2025, or roughly a 35 percent increase (United StatesCensus Bureau, 1998). In simplistic terms and assuming little or no change inworld per caput consumption of wheat, a projection of 786 million tonnes ofwheat will be required annually for human use in the year 2025, an annualproduction increase of 204 million tonnes above production in 1997. Thisunderscores the need to rapidly and continuously increase production. Greaterwheat 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 forconsumption.

Area expansion

Due to other agricultural and non-agricultural uses, anincreased area of productive agricultural lands is not likely to be availablefor wheat production. Thus, any increased land area for wheat will, ofnecessity, come from the use of more marginal or non-traditional areas. Improvedcultivars and cultural techniques have been under development by plant breedersand agronomists for several years to allow wheat to be grown under more adverseconditions, such as in acid and saline soils, with greater heat tolerance and inmore tropical environments. Considerable progress has been achieved toward theseimprovements, but further research will be necessary to ensure stable wheatproduction under the more difficult environments required for areaexpansion.

Social and economic incentives that encourage farmers to adoptprogressive agricultural technologies are also necessary. Since most potentialfarmers in non-traditional areas operate at a subsistence level, newagricultural technologies must be profitable. In most countries, theestablishment of government programmes to facilitate adequate distribution ofinputs to farmers and delivery of their increased production to the market willbe necessary.

Yield improvement

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

Current research to improve wheat yields covers a broad frontand includes further mixing of germplasm through crossing, interspecific andintergeneric hybridization, biotechnology techniques, hybrid wheat, basicstudies on the physiology of the wheat plant and on the host-plant relationshipsof various pests that attack it and numerous other important researchavenues.

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