Wheat A Global Crop

Wheat is now grown on each continent, and, in terms of its total production is one of the world's two most important cereal crops. Only rice rivals it, and maize, barley, sorghum, millets, rye, and oats come behind (Table 2.1). Unraveling the origins of wheat as a global crop involves two sorts of questions. First, what are the botanical origins of the different types of wheat? Second, what role did the evolving wheats play in the origins of agriculture as a mode of human life? Studies in archaeology, paleoethnobotany, cytogenetics, and plant biochemistry in the past forty years have been combined to suggest that the answers to these two questions are completely and inseparably intertwined.

How wheat originated as a botanical species has long occupied the thoughts of scholars, philosophers, priests, and scientists. For the Greeks, Romans, and ancient

Table 2.1 Worldwide major cereal crop production levels, 1993-94 to 1995-96

Crop (million tons)

Table 2.1 Worldwide major cereal crop production levels, 1993-94 to 1995-96

Crop (million tons)

Year

Wheat

Rice"

Coarse Grains

All Cereals

1993-94

565

529

803

1,896

1994—95b

528

540

884

1,952

1995-96«

550

545

839

1,933

aPaddy (grain before milling).

bEstimated.

cForecast.

aPaddy (grain before milling).

bEstimated.

cForecast.

Source: Food and Agriculture Organization, Food Outlook, no. 5-6, May-June 1995, p. 2.

Chinese, the existence of wheat was connected to divinity. The Greeks, for example, considered wheat the gift of Demeter, goddess of the fruitful soil. Ceres was the counterpart of Demeter in Roman mythology,15 and our English word "cereal" is derived from this ancient deity.

Science has preferred natural rather than supernatural stories for the origin of wheat. A series of studies in the twentieth century have indicated that wheat in its many varieties was the product of a complex series of hybridizations among what originally were wild grasses of southwestern Asia (Figure 2.3). Some of these hybridizations occurred most probably under conditions of cultivation, that is, after wheat had been domesticated for agriculture.

The first hybridization of importance to the origins of Triticum aestivum was probably a cross between two wild grasses, Aegilops sitopsis and Triticum urartu. Each of the two wild grasses was a diploid with fourteen chromosomes. The hybrid between them, Triticum dicoccoides, was a tetraploid with twenty-eight chromosomes.16 Once formed, Triticum dicoccoides tended to "breed true," that is, pollen tended to fertilize ovules on the same plant so that each new generation would be like its parents. Such self-fertilizing plants were prominent among the plants domesticated in southwestern Asia. This trait helped keep the newly domesticated varieties from interbreeding with their weedy progenitors.17

Considerable uncertainty still surrounds the question of when and how Triticum dicoccoides became the domesticated Triticum dicoccum, but little doubt remains

Triticum Grains
Figure 2.3 Origins of cultivated wheats from wild grasses. Numbers in parentheses refer to number of chromosomes. Line drawing by Tim F. Knight. Adapted from T. E. Miller, Systematics and Evolution, in Wheat Breeding: Its Scientific Basis, ed. F. G. H. Lupton (London: Chapman and Hall, 1987), p. 22.

that the cultivated variety was being farmed as early as 7800 B.C. By about 6000 B.C. it was being farmed in southeastern Europe, and by 3000 B.C. in Egypt, the Mediterranean basin, Europe, central Asia, India, and Ethiopia.18

Triticum dicoccum, also known as emmer, was almost certainly the dominant wheat in Neolithic farming, but at an early stage of agriculture it gave rise to what we now call Triticum aestivum, or common bread wheat. Cytological studies of wheat chromosomes suggest that bread wheat resulted from the hybridization of Triticum dicoccum, a tetraploid with twenty-eight chromosomes, with the wild diploid (fourteen chromosomes) gmssAegilops squarrosa. Bread wheat, as a result, is a hexaploid with forty-two chromosomes. Archaeological evidence suggests that hexaploid wheat may have been cultivated as early as 7000 B.C.,19 certainly by 5000 B.C.20

Triticum dicoccum also gave rise to the other major variety of contemporary wheat, Triticum durum, or macaroni wheat. Triticum durum is a tetraploid wheat, too, but it differs from its progenitor in having a free-threshing grain with a tough, non-shattering ear, that is, the grain detaches from the ear during threshing without bringing along the rachis (backbone of the ear) or the glumes (chaff). Triticum aestivum is also free-threshing. The difference between free-threshing varieties that give a naked grain and those that give the hulled grains lies in one genetic trait, with the free-threshing form being dominant to its counterpart.21

Free-threshing was a trait that admirably suited a cereal for human use because the grain remained in the harvested ear until threshed. Ears that were not free-threshing tended to "shatter" or break apart, an adaptation that helped disperse seed in a non-domesticated plant. A plant that was nonshattering or free-threshing was dependent upon people for dispersal and propagation of the next generation. This mutation was one of the key changes in wheat that created the wheat-human codependency.22

During the Neolithic agricultural revolution, the dominance of emmer (Triticum dicoccum), a tetraploid, as the major cultivated grain was rivaled and sometimes surpassed by Triticum monococcum, a diploid, also known as einkom, from the German meaning "one kernel." Each spikelet produces only one grain rather than the three or more that are characteristic of bread and macaroni wheats. Wild einkorn was probably collected as early as 9000 B.C. and was definitely one of the first cultivated forms of wheat. Einkorn, like emmer, spread to Europe and continues to be cultivated there in small amounts.23

We are particularly interested in the spread of wheat to the four countries critical to the development of high-yielding varieties in the years after 1940: England, Mexico, the United States, and India. In England (Figure 2.4) and India (Figure 2.5), wheat came several thousands of years ago and has been cultivated every year since then. In many respects both England and India are "wheat civilizations" in the sense that this cereal was a prime component of their existence as settled societies. Wheat came later to the United States and Mexico because it was an Old World crop that did not reach the New World until Columbus's voyage of 1493.

Wheat arrived in England thousands of years after Britain was colonized by people. Archaeological evidence suggests that agriculture came to Britain around 3200 B.C.,24 about 3,000 years after the melting and receding glaciers had raised sea levels and cut the land link between Britain and continental Europe. Emmer and barley were the major cereals, but also of importance were einkorn, flax, bread (hexaploid) wheat,

British Isles Map Drawing

Figure 2.4 Major wheat-producing areas of England. Line drawing by Tim F. Knight. Outline of map adapted from National Geographic Society, British Isles (1:1,687,000) (Washington, D.C.: National Geographic Society, 1979), 1 p. Wheat-growing areas adapted from U.S. Department of Agriculture, Major World Crop Areas and Climatic Profiles (Washington, D.C.: U.S. Department of Agriculture, 1987), Agriculture Handbook no. 664.

Figure 2.4 Major wheat-producing areas of England. Line drawing by Tim F. Knight. Outline of map adapted from National Geographic Society, British Isles (1:1,687,000) (Washington, D.C.: National Geographic Society, 1979), 1 p. Wheat-growing areas adapted from U.S. Department of Agriculture, Major World Crop Areas and Climatic Profiles (Washington, D.C.: U.S. Department of Agriculture, 1987), Agriculture Handbook no. 664.

Roman Crop Areas

Figure 2.5 Major wheat-producing areas of India and Pakistan. Line drawing by Tim F. Knight. Outline of map adapted from National Geographic Society, South Asia with Afghanistan and Burma (1:6,522,000) (Washington, D.C.: National Geographic Society, 1984), 1 p. Wheat-growing areas adapted from U.S. Department of Agriculture, Major World Crop Areas and Climatic Profiles (Washington, D.C.: U.S. Department of Agriculture, 1987), Agriculture Handbook no. 664.

Figure 2.5 Major wheat-producing areas of India and Pakistan. Line drawing by Tim F. Knight. Outline of map adapted from National Geographic Society, South Asia with Afghanistan and Burma (1:6,522,000) (Washington, D.C.: National Geographic Society, 1984), 1 p. Wheat-growing areas adapted from U.S. Department of Agriculture, Major World Crop Areas and Climatic Profiles (Washington, D.C.: U.S. Department of Agriculture, 1987), Agriculture Handbook no. 664.

and spelt (probably Triticum spelta, a hexaploid wheat that has an easily shattered ear and yields hulled grain with the glumes or chaff tightly attached).25

Wheat arrived in India somewhat before it arrived in England, about 4000 B.C. Remnants of tools and weapons, dating to as many as 200,000 to 400,000 years ago, suggest that people from East Asia were the first to migrate into the northern parts of present-day India, while people from East Africa were the first migrants to the south. Little connection seems to have existed between the two, distinct cultures. Despite the relative nearness of India to southwestern Asia, the Neolithic agricultural revolution did not reach India until nearly 4,000 years after the first traces of wheat agriculture can be found in southwestern Asia.26

Regardless of why it may have taken a long time for the cultivation of wheat and barley to intrude into South Asia, one of the world's first complex and monumental societies eventually emerged along the course of the Indus River in what is now modern Pakistan. Harrapan culture, named after the major ancient city at Harrapa, thrived from about 2500 to 1600 B.C. At its peak the Indus civilization stretched into what are now the Indian states of Rajasthan and Gujarat. Wheat was its most important crop, but these people were also the first to begin using cotton for cloth, and they also relied on rice, peas, dates, mustard seeds, and sesamum. They also had domesticated many animals, including dogs, cats, camels, sheep, pigs, goats, water buffalos, zebus, elephants, and chickens.27 To this day, wheat remains a foundation stone of the modern Indian civilization.

Human settlement of what is now the United States and Mexico (Figure 2.6) came much later than the Old World settlements of India and England. People were surely in those latter two places over 300,000 years ago, but humans probably did not reach the Americas earlier than about 40,000 years ago.28 Wheat did not yet exist before the land bridges to North America flooded with the retreating ice and isolated the American continents from Eurasia. Therefore, the first people in the Americas had no wheat or any other Old World cereal. Complex civilizations emerged on the basis of maize and other seed crops in the Tehuacan valley in Mexico and from root crops such as manioc, sweet potato, achira, and potato in the lowland and highland areas of what is now Peru.29

Wheat came to the Americas with European invaders. Columbus recorded bringing wheat, beans, and chickpeas on his second voyage in 1493. The Spanish conquest of Mexico led to wheat and barley being grown around Mexico City by 1535 and exported to the West Indies. As the Spanish invasion spread northward to what is now Texas and New Mexico, wheat went along. French exploration and conquest of Louisiana also brought wheat into Texas in the eighteenth century.30 Similarly, the invading English brought wheat with them to North America, planting wheat at Jamestown in 1607, and subsequent waves of settlers brought wheat to other European outposts.31 Wheat now ranks as one of the foundations of New World agriculture. Only maize rivals it in terms of total production.

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  • michael
    When did wheat arrive in north america?
    9 years ago
  • Galeazzo
    How is cut the british isles?
    8 years ago
  • Jukka-Pekk H
    What is the origin of the English word cereal?
    8 years ago
  • Mikolaj
    How many Production of wheat after green revolution in world ?
    4 years ago

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