Wheat. Peter R. Shewry

are increasingly aware that the interdependency between wheat and humans has implications for our health and environment. Our understanding of this association informs how we plan to maintain food supplies, how we attempt to sustain the quality of our nutrition, and how we strive to protect the ecosystems on which we depend: for ourselves and future generations.

      It has not always been like this. For at least 95% of their time on earth, modern humans existed as sparse groups of mobile hunter‐gatherers. From around 12 000 years ago (before present, BP), however, there is scattered evidence of sedentism. It is not certain that this change from nomadic to sedentary behaviour resulted from the need to tend plants such as wheat, but from 10 500 to 8000 BP there is evidence of increased planting. Over the following millennia, the settlements became organised into states which were largely founded, funded, and organised around the production of grain from grasses such as wheat (Scott 2017). Increases in production have been associated with political and military strength (Perkins 1997) while interruptions in the supply of wheat and its products continue to contribute to famine, civil unrest, and conflicts (Bellemare 2015).

If the mobility of the hunter‐gatherers vs. sedentism, and freedom from states vs. state control are articulated as conflicts (e.g. Scott 2017), then we should also recognise a further battle, one in which humans have only recently joined: that between the trees and the grasses (the Poaceae). This war has been playing out since the origins of the grasses, perhaps 70 million years ago (MYA) (Thomas 2017). The grasses are flowering plants (angiosperms) that have one seed leaf (monocotyledon). They produce a fruit of one seed (a caryopsis) with a mature embryo to facilitate rapid establishment. Compared with most trees, grasses are drought tolerant (Chapter 3). They can either recover or establish rapidly after dry spells and fires (Chapman 1996). Many of them, including wheat (Gooding et al. 1998), can survive being grazed for a significant part of their life cycle; again, this is an advantage over the trees. Humans have strongly backed the grasses: through clearance of forests by fires; through grazing with livestock; and most recently through soil cultivation and planting. Today the cultivated grasses are commonly grown on soils that developed under trees (Chapter 2). Grasses, including those grown for grain (717 million ha [Mha]) and for sugar cane (27 Mha), with the land covered in permanent meadows and pastures (3400 Mha; O'Mara 2012), together account for 85% of the world's agricultural land.

      Wheat is a cereal. The cereals are grass plants grown primarily for their seeds to be used as a foodstuff. We name them after the Roman god of food plants, Ceres. For early gatherers and then farmers, cereal grains provided a concentrated source of nutrients. Wheat, like other cereals, is multifunctional, providing carbohydrates (mostly starch), protein, fat, minerals, vitamins, and fibre. Growing wheat would have been comparatively easy; wild wheats still grow in dense stands today without assistance (Evans 1993; Fu et al. 2019). Although the natural dispersal mechanisms of wheat were compromised during domestication, a seed merely falling on good soil has always been capable ‘of multiplying thirty, some sixty, some a hundred times’ (Mark's Gospel c. 65 Christian Era [CE]). Some early forms of agriculture just involved broadcasting seeds onto the fertile and damp silts left by a retreating annual river flood (Scott 2017). In a modern‐day equivalent, in some rice‐wheat systems, the wheat is still established by broadcasting seed onto wet soils before or after the rice harvest (Erenstein and Laxmi 2008). Cereal grains are dry, easy to reap, simple to store, and readily transported (Evans 1993). In comparison, roots and tubers are moist, bulky, perishable, and more labour intensive to harvest and move. Compared to the early legume grain crops such as peas, beans, chickpeas, and lentils, cereal growth is more determinate. This meant that the cereal grains tended to ripen together rather than over an extended duration, depending on their position within an inflorescence and on the maturity of different stems and branches. The cereals could, therefore, be harvested efficiently over a shorter period. In terms of importance for state building, Scott (2017) emphasises the suitability of cereals for paying tribute and taxes, and for providing rations and payment. The cereal crops were ‘visible, divisible, assessable, transportable’ (Scott 2017). Additionally, cereal straw was valued for multiple uses, including roofing, livestock fodder, and animal bedding (Sinclair 1998).

The early adoption of the cereals, and their subsequent importance for the growth and functioning of states, had consequences that increased their dominance to current times. Economically and politically, it is easier to justify investment in research, plant breeding, fertilizer and irrigation technology, agrochemical discovery, machinery improvement, advisory and education services, processing technology, and trading efficiency for the most important crops such as wheat (e.g. Perkins 1997). Investment results in greater competitive advantage and further increased status. This is a continuing process that contributes to other pressures for agricultural systems to become simpler. That is, there is a tendency to focus on fewer crops, which are grown and processed with increasing efficiency.

World crop production is now dominated by the cereals (Figure 1.1). Nine of the twenty‐two most important grain and oilseed crops are cereals, and they account for c. 85% of all grain and oilseed production. In comparison with the roots and tubers, the cereal area of over 700 Mha dwarfs that of cassava (27 Mha), potatoes (17 Mha), yams (9 Mha), and sweet potatoes (8 Mha). Similarly, the major perennial plantation crops of sugar, tea, bananas, plantains, coffee, cocoa, coconuts, rubber, and oil palm only account for c. 125 Mha in total. Wheat is one of the few major crops: one of the big three with maize and rice (Figure 1.1c).

The major factors in the widespread adoption of wheat, leading to its current pre‐eminence, have been its perceived superiority for human consumption, its unique processing properties, and its wide adaptation to different climatic conditions. Consequently, while barley, oats, and rye have been the dominant cereals in different times and places, even in temperate areas, none have matched the reputation of wheat as a human food. Indeed, higher proportions of barley, oats, and rye were traditionally relegated to the feed of livestock and draft animals (Wrigley 2009). Wheat is now produced on a greater area and grown over a wider geographic range than any other arable crop. It is also the arable crop most traded internationally as a commodity (Figures 1.1 and 1.2). It accounts for over a quarter of all cereal production. Wheat alone provides 20% of the calories and protein in the global human diet, a greater contribution than from either maize or rice (Shiferaw et al. 2013). Dependency on wheat is particularly high in areas of North Africa, the Middle East, and Central Asia, where wheat often contributes more than 50% of daily calorific intake (e.g. Figure 1.3). The top 10 wheat‐producing countries are China, India, Russian Federation, USA, France, Canada, Pakistan, Ukraine, Australia, and Germany (Table 1.1). These account for 70% of global production, with Asia and Europe accounting for 44% and 34%, respectively.

Figure 1.1 The world production and exports of grain and oilseeds.

      Source: Data are means of 2015–2019 from FAOSTAT (FAO 2021).

Figure 1.2 The global distribution of wheat production. Shading intensity represents estimated yield × area per pixel. Further details on the climate of the labelled major areas of production given in Figure