Common wheat

• 1. Introduction

  ›

  Common wheat, Triticum aestivum, is the single most widely grown crop on earth. It accounts for roughly 95% of all wheat produced worldwide, and of every cereal grown for human use, it generates the highest monetary yield. Those numbers raise an immediate question: how did one species come to dominate global agriculture so completely, and what is it about this particular plant that made it so well suited to the modern world? The answers reach back to the early Holocene, run through ancient Rome and the Spanish missions of the 16th century, and pass through a laboratory in Japan that quietly changed the way farmers grow food everywhere.

• 2. A Genome Built From Three

  ›

  Bread wheat carries six complete sets of chromosomes inside each of its cells. Four of those sets came from emmer wheat, Triticum turgidum, itself already a tetraploid. The remaining two sets came from Aegilops tauschii, a wild diploid goatgrass. That combination makes bread wheat an allohexaploid, a word that simply means its genome was assembled from the genomes of different ancestral species. Emmer itself was not a simple organism. It arose from an earlier hybridization between two diploids: wild einkorn, Triticum urartu, and Aegilops speltoides, another wild goatgrass. So the family tree of a single loaf of bread wheat traces through at least three distinct wild ancestors. Free-threshing wheat, the form that sheds its grain easily, is closely related to spelt. The contribution from Aegilops tauschii gave bread wheat greater cold hardiness than most of its wheat relatives, which helps explain why it can be cultivated across the world's temperate regions.

• 3. From West Asia to the World

  ›

  Common wheat was first domesticated in West Asia during the early Holocene. From that starting point it spread across North Africa, Europe, and East Asia during the prehistoric period, long before written records could track it. Naked wheats, the class that includes Triticum aestivum, T. durum, and T. turgidum, have turned up in Roman burial sites dated from 100 BCE to 300 CE, which tells us the grain was present across the Roman world for at least four centuries. Wheat crossed the Atlantic when Spanish missions arrived in North America in the 16th century, but the continent did not become a major grain exporter until the colonization of the prairies in the 1870s. World War I provided another acceleration: as grain exports from Russia stopped, production in Kansas alone doubled. Worldwide, bread wheat proved better adapted to industrial baking than barley or rye, and gradually displaced those species from European bread making.

• 4. Norman Borlaug and the Short Stem

  ›

  Modern bread wheat looks physically different from its ancestors, and one agronomist is responsible for that transformation. In the 1960s, Norman Borlaug introduced genes called RHt dwarfing genes into modern wheat varieties by crossing them with Norin 10 cultivars, a type of wheat developed in Japan. RHt genes reduce a plant's sensitivity to gibberellic acid, a plant hormone that causes cells to elongate. When heavy applications of chemical fertilizer are applied to tall-stemmed wheat, the stems grow so high that they collapse under the weight of the grain, a problem farmers call lodging. Short-stemmed varieties avoid that collapse. Even stem heights also matter for a second reason: modern mechanical harvesting equipment works best when every plant in the field stands at roughly the same height. Borlaug's work with these dwarfing genes became a central feature of what became known as the Green Revolution, and the Norin 10 cultivar at the heart of that work had originated in Japan before reaching his hands.

• 5. Naming a Moving Target

  ›

  Wheat has been cultivated and selected by humans for so long that its diversity has generated genuine scientific confusion. Varieties have been named on the basis of genetic characteristics, and separately on the basis of physical characteristics, and those two systems do not always agree. Named cultivars of common wheat include Albimonte, Manital, Shirley, and Hilliard, each representing a distinct form selected for particular traits. Compact wheats, such as club wheat, Triticum compactum, and in India a form called T. sphaerococcum, are closely related to common wheat but have a much more compact ear. Their spikelets are packed more tightly together because the rachis segments, the portions of the seed head between each spikelet, are shorter. Taxonomists often treat compact wheats not as separate species but as subspecies of Triticum aestivum, classifying them as T. aestivum subsp. compactum. That ongoing negotiation between common usage and formal taxonomy reflects how deeply human agriculture has shaped and reshuffled this one plant species across millennia.