Barley

Barley (Hordeum vulgare), a member of the grass family, is a major cereal grain grown in temperate climates globally. One of the first cultivated grains, it was domesticated in the Fertile Crescent around 9000 BC, giving it nonshattering spikelets and making it much easier to harvest. Its use then spread throughout Eurasia by 2000 BC. Barley prefers relatively low temperatures and well-drained soil to grow. It is relatively tolerant of drought and soil salinity, but is less winter-hardy than wheat or rye.

In 2023, barley was fourth among grains in quantity produced, 146 million tonnes, behind maize, rice, and wheat. Globally, 70% of barley production is used as animal feed, while 30% is used as a source of fermentable material for beer, or further distilled into whisky, and as a component of various foods. It is used in soups and stews and in barley bread of various cultures. Barley grains are commonly made into malt using a traditional and ancient method of preparation. In English folklore, John Barleycorn personifies the grain and the alcoholic beverages made from it. English pub names such as The Barley Mow allude to its role in the production of beer.

The Old English word for barley was bere. This survives in the north of Scotland as bere; it is used for a strain of six-row barley grown there. Modern English barley derives from the Old English adjective bærlic, meaning "of barley". The word barn derives from Old English bere-aern meaning "barley-store". The name of the genus is from Latin hordeum, barley, likely related to Latin horrere, to bristle.

Barley is a cereal, a member of the grass family with edible grains. Its flowers are clusters of spikelets arranged in a distinctive herringbone pattern. Each spikelet has a long thin awn (to 160 mm (6.3 in) long), making the ears look tufted. The spikelets are in clusters of three. In six-row barley, all three spikelets in each cluster are fertile; in two-row barley, only the central one is fertile. It is a self-pollinating, diploid species with 14 chromosomes.

The genome of barley was sequenced in 2012 by the International Barley Genome Sequencing Consortium and the UK Barley Sequencing Consortium. The genome is organised into seven pairs of nuclear chromosomes (recommended designations: 1H, 2H, 3H, 4H, 5H, 6H and 7H), and one mitochondrial and one chloroplast chromosome, with a total of 5000 Mbp. Details of the genome are freely available in several barley databases.

The barley genus Hordeum is relatively closely related to wheat and rye within the Triticeae, and more distantly to rice within the BOP clade of grasses (Poaceae). The phylogeny of the Triticeae is complicated by hybridization between species, so there is a network of relationships rather than a simple inheritance-based tree.

Barley was one of the first grains to be domesticated in the Fertile Crescent, an area of relatively abundant water in Western Asia, around 9,000 BC. Wild barley (H. vulgare ssp. spontaneum) ranges from North Africa and Crete in the west to Tibet in the east. A study of genome-wide diversity markers found Tibet to be an additional center of domestication of cultivated barley. The earliest archaeological evidence of the consumption of wild barley, Hordeum spontaneum, comes from the Epipaleolithic at Ohalo II at the southern end of the Sea of Galilee, where grinding stones with traces of starch were found. The remains were dated to about 23,000 BC. The earliest evidence for the domestication of barley, in the form of cultivars that cannot reproduce without human assistance, comes from Mesopotamia, specifically the Jarmo region of modern-day Iraq, around 9,000–7,000 BC.

Domestication changed the morphology of the barley grain substantially, from an elongated shape to a more rounded spherical one. Wild barley has distinctive genes, alleles, and regulators with potential for resistance to abiotic or biotic stresses; these may help cultivated barley to adapt to climatic changes. Wild barley has a brittle spike; upon maturity, the spikelets separate, facilitating seed dispersal. Domesticated barley has nonshattering spikelets, making it much easier to harvest the mature ears. The nonshattering condition is caused by a mutation in one of two tightly linked genes known as Bt₁ and Bt₂; many cultivars possess both mutations. The nonshattering condition is recessive, so varieties of barley that exhibit this condition are homozygous for the mutant allele. Domestication in barley is followed by the change of key phenotypic traits at the genetic level.