Barley ( P h o t o : R o b i n A p p e l . )

Figure 1: Cultivated barley. The domestication of barley

The origin of agriculture is one “How great is the power of man in Wild barley of the seminal events in human accumulating by his Selection The wild ancestor of barley is well culture. The development of documented, and has been traditionally domestic animals and crops successive slight variations...” described as Hordeum spontaneum C. Koch ., a wild, large-seeded barley. Originally from wild species laid the HARLES ARWIN N THE RIGIN OF PECIES C D , O O S , 1859 considered a separate species, this plant is, in foundation for the Neolithic fact, a subspecies of the cultivated crop, revolution some 10,000 –12,000 cultivation of plants selected from the wild because the wild type is cross-compatible and years ago and resulted in the (but not yet genetically different from wild fully interfertile with cultivated barley. Since transition of hunter-gatherer plants) and terminates in fixation, through there are no biological barriers to groups to sedentary, pastoral human selection, of morphological (hence hybridisation between wild and cultivated and farming societies. genetic) differences distinguishing a barley, all forms are now deemed to belong to domesticate from its wild progenitor. These a single biological species ( H. vulgare ) and, differences make up the ‘domestication as a result of gene-flow, any rigorous by Ian Hornsey syndrome’ and usually render the domesticate taxonomic distinction between wild and less capable of surviving in the wild (i.e. cultivated forms is always going to be become dependent on man). As well as loss of problematical. Accordingly, the scientifically griculture in the Old World appears to seed dispersal mechanism, other features of correct designation for the wild type is A have arisen in several key centres, the syndrome include, increase in seed size, therefore H. vulgare L. subp. spontaneum including the Fertile Crescent in the Near East loss of seed dormancy and loss of chemical or (C.Koch) Thell. (although, henceforth, we’ll and the middleYangtze River Valley in China. mechanical protection against herbivores. call it H. spontaneum ). Then, strictly, There has long been an interest in the Cultivated barley ( Hordeum vulgare L. – cultivated barley becomes H. vulgare subsp. mechanisms by which agriculture was Figure 1), is a diploid (2n = 14) and mostly vulgare. disseminated from these sites of origin. Only self-pollinated crop of which hundreds of Both wild barley and the first cultivated by studying the origins and migrations of modern varieties and land races are known. forms were morphologically similar, and were cultivated crops such as barley are we likely Although mainly grown today for animal feed two-rowed and ‘hulled’ (i.e. the husk adhered to be able to ascertain the origins of brewing. and for brewing/distilling, barley was an to the grain). The husk is rich in silica and Since the onset of the genomic age, studies of important cereal food in the past. Any doubt would have to be removed by pounding barley domestication have progressed rapidly. about the use of barley in bread-making can before the grain is suitable for consumption. During this agricultural revolution, ancient be dispelled by referring to the Bible, where In ‘naked’ barleys, the husk does not adhere to people saved seeds from plants with favoured Ezekiel (4:9) says: “Take thou also unto thee the grain and can be easily removed by traits for the next generation (sowing), and wheat, and barley, and beans, and lentils, and threshing. over time they converted seemingly millet, and spelt, and put them in one vessel H. spontaneum (Figure 2) can still be found unpromising wild species into reliable, and make thee bread thereof...” growing today around the eastern productive crops. Domestication is the end- It is probably only since the Middle Ages that Mediterranean basin and western Asia (Figure point of a continuum that starts with the the role of barley as a staple food has declined 3), where it occupies primary habitats. exploitation of wild plants, continues through in most areas. Morphologically, it is rather difficult to

Brewer & Distiller International • December 2010 • www.ibd.org.uk 41 Barley ( ( P I m h o a t g o e : : D O r s x f M o r a d r k U N n i e v s e b r i s t t i t a y n P d r D e s e s l . w ) e n S a m u e l . )

Figure 3. Distribution of wild barley. The area in which wild barley is massively spread is shaded – the ‘Fertile Crescent’. Dots represent additional sites, mainly weedy forms. Wild barley extends further eastwards – as far as Tibet.

wild populations. It may, however, quickly be now submerged Late Stone Age, site on the selected for in a population that is subjected to southern shore of the Sea of Galilee, and the man-made environment of reaping, dating from ca. 17,000 BC. Other early threshing and sowing. Experimental field evidence of H.spontaneum collection from trials and computer simulations indicate that, the wild comes from another Late Stone Age under certain conditions, the recessive (non- site at Tell Abu Hureyra, in northern Syria brittle) genotype may become predominant in (9000 BC) ; Tell Mureybit (Late Stone Age, 8- a remarkably short time (around 20 years!). 7500 BC.), also in northern Syria, and Tell Aswad, some 25km. south-east of Damascus, Barley domestication at a site dated to 7800 – 7600 BC. The kernel The received wisdom has been that barley specimens recovered at these sites were domestication was a single event essentially identical to present-day wild (monophyletic) and that the domesticate barley, being two-rowed with a brittle rachis. Figure 2. Hordeum spontaneum – growing on spread with human migrations, but the small The earliest signs of the cultivation of barley the Plain of Konya, Turkey. differences between wild and domesticated emanate from a later (Neolithic; ca. 7500 BC barley and the apparent ease with which wild onward) level at Tell Abu Hureyra; from forms become domesticated, has led some phase II (ca. 6900-6600 BC) in Tell Aswad distinguish between wild H. spontaneum and workers to suggest that barley domestication and from 6400 BC pre-pottery Jarmo, Iraq. At cultivated two-rowed varieties, since they must have occurred more than once (i.e. was all of these sites cultivated, non-brittle, barley differ primarily in their methods of seed polyphyletic). Such agricultural historians heads have been found, together with the wild structure (Figure 4) and dispersal; H. and geneticists alike think that the crop was type. The earliest domesticated barley to be spontaneum has brittle ears (spikes) which, at domesticated in dispersed small areas and recovered (ca. 7500 – 6,400 BC) also had maturity, disarticulate into individual wedge- spread by human migrations and trade. two-rowed spikes. shaped spikelets. These fragments are highly Most archaeological evidence suggests that Cultivation of six-rowed barley was specialised devices which ensure the survival barley domestication went hand in hand with apparently a little later, with estimated dates of the plant in the wild. In wild barley, with the evolution of Neolithic villages in the being in the 6,800-6,000 BC range. Then, rudimentary lateral rows of spikelet, there is Levantine arc of the ‘Fertile Crescent’. around 5,000-4,000 BC, when barley became no impediment to seed dispersal after Late Stone Age peoples in this area became widely cultivated in the alluvial soils of shattering of the spike. increasingly dependent on plant foods for Mesopotamia (and, later, in Lower Egypt), the Wild barley has complementary genes, Btr1 their existence and may have cultivated six-rowed form soon became dominant and and Btr2, which control the formation of the plants. The earliest signs of the pre- ousted its two-rowed sister to become the brittle rachis and cultivated barley carries agricultural gathering of wild barley (together most important crop in these early mutant recessive alleles (btr1 and btr2) which with wild emmer wheat) are from Ohalo II, a civilizations. are tightly linked and result in a non-brittle About fifty years ago, Danish botanist Hans rachis. All cultivated barleys have either one Helbaek noted that evidence strongly of the two recessive alleles and there is suggested that two-rowed barley was brought evidence that most occidental cultivars have into cultivation earlier than its six-rowed the brt1 allele while most oriental forms carry counterpart, but that there were spatial btr2. In wild forms, seeds are regularly differences in their spread. Both two-and six- scattered on the ground as the stalk shatters – rowed barleys emerged in Greece between this makes them difficult for humans to 6,000 and 4,000 BC, but the six-rowed form gather. After the lethal (for wild populations) dominated in the Balkans and central Europe mutation, the seeds fail to drop and are (3,000 BC – to around the birth of Christ) and conveniently concentrated on the stalk for in southern Europe and North Africa humans to gather. (5,000 –2,000 BC) and he also noted that after The loss of a brittle rachis is one of the its disappearance from Mesopotamia and most critical traits in the evolution and ancient Egypt it does not reappear in the domestication of barley and the mutation Figure 4: Cross-sections of wild and archaeological record of these two regions mentioned above will rarely occur in totally cultivated barley. until about AD 900. Cultivation of two-rowed

42 Brewer & Distiller International • December 2010 • www.ibd.org.uk Barley ( P h o t o : D r P a m e l a R o s e , E E S . )

Figure 5: Spikelets at a rachis node: A: 2-row cultivar; B: 2-row wild; C: 6-row cultivar. Figure 6. Barley sample from Qasr Ibrim. barley is virtually unrecorded in central and lateral spikelets. In all barley varieties the How the six-rowed southern Europe until AD 1000 and some median spikelet is fertile and develops a grain condition is formed authorities have assumed that it was which invariably has its ventral or grooved The two-rowed condition is considered to be introduced into Europe around AD 1100-1200 side next to the broad face of the rachis. The more primitive, mainly on grounds of the fact by crusaders returning from the Near East. exact way in which the spikelets develop in that wild barley has that phenotype. The Barley has been continuously cultivated for domesticated forms gives us two main types difference in spikelet type is governed over 8,000 years in southern Central Asia, (see Figure 5.): primarily by a single allele vrs1, which is east of the Fertile Crescent and there has been 1) Two-rowed (traditionally called Hordeum recessive to the dominant allele (Vrs1) much debate as to whether it was distichum L. ), in which only one median responsible for the two-rowed spike. The domesticated there locally or imported along spikelet in each triplet is fertile and usually presence of the recessive gene vrs1 is, by with other crops from the Fertile Crescent. bears a prominent awn. The two lateral itself, sufficient to cause two-row barley to Recently, a team from the University of spikelets are reduced and borne on longer become six-row barley, even though other California at Irvine presented genetic stalks. They contain no grains and have no genes may be associated with the change evidence which inferred that there was awns, and so each ear contains just two (such as those responsible for seed weight, another centre of barley domestication some rows of fertile spikelets. protein content and β-glucan content). 1,500 –3,000 km to the east of the Fertile 2) Six-rowed forms (traditionally referred to In 2007, a team led by Takao Komatsuda Crescent (at the eastern edge of the Iranian as Hordeum hexastichum L .), in which all reported precise information about the actual Plateau). It was proposed that the Fertile three spikelets in each triplet bear seed and origin of six-rowed barley when they found Crescent domestication contributed the usually all are awned. Ears in these forms that a mutant homeobox gene was responsible majority of the diversification in European have six rows of fertile spikelets. for the two-row to six-row transition. First, and American cultivars, whereas the second the team isolated the six-rowed spike 1 (Vrs1) domestication contributed most of the The above indicates that, because of striking gene by a process called ‘gene walking’ and diversity in barley from Central Asia to the differences in ear (and kernel) morphology, then discovered that this gene encodes a Far East. It has been recognised for some time taxonomists regarded two- and six-rowed homeodomain protein (a potential that East Asian barleys differ from European barleys as distinct species. A number of transcription factor). The normal expression and North African landraces in terms of the varieties have been invoked as well, including of Vrs1 is a protein called VRS1, and this was incidence of a naked caryopsis and the dense eared forms that tend to stand upright found to be localised in the lateral spikelet prevalence of two-rowed vs. six-rowed forms. (var. erectum ); forms where the grains and primordia of immature spikes (suggesting that At the turn of the new millennium it was awns may spread out like a fan ( var. this protein suppresses the development of the reported that, on the basis of the fact that wild zeocrithon ), and lax-eared forms with the lateral rows of spikelets). Thus, loss of barley populations from Israel/Jordan are tendency to bend over and ‘nod’ ( var. nutans ) function of Vrs1 (and hence a lack of VRS1) molecularly more similar than are any others When six-rowed barleys have lax ears, the enables the complete conversion of the to the cultivated gene pool, then this is the lateral rows of grains tend to overlap, giving rudimentary lateral spikelets in, what would likely region that barley was first brought into rise to what are known as ‘four-rowed’ otherwise be, two-rowed barley into fully culture. On-going genetically-based research barleys. This is a misnomer, although H. developed fertile spikelets (i.e. the six-rowed is showing that the origin and diffusion of tetrastichum was assigned to such forms at phenotype). Simple when you know how! A barley might be much more complex than one time. phylogenetic analysis of Vrs1 alleles previously thought. demonstrated that the six-rowed phenotype originated repeatedly, at different times and in Two-rowed and six-rowed barley different regions, through independent In the barley ear three single-flowered In 2007, a team led by Takao mutations of that particular allele. spikelets are borne at each node of the rachis. Komatsuda reported precise These alternate on the rachis so that the triplet information about the actual origin An anomaly? of spikelets immediately above or below any of six-rowed barley when they found The discovery of a wild form of six-rowed one triplet is on the opposite side of the rachis that a mutant homeobox gene was barley (i.e. with brittle rachises), which was or axis of the ear. This arrangement gives six responsible for the two-row to called ‘ H. agriocrithon ’, in the south-west rows of spikelets. The middle spikelet of each six-row transition. Chinese province of Sichuan in the late- triplet is usually termed the median spikelet 1930s, was originally viewed as evidence for and the two flanking it, one on either side, the “ this region being a centre of domestication. ” Brewer & Distiller International • December 2010 • www.ibd.org.uk 43 Barley ) .

S the mechanism of lateral floret inhibition E E

, here was more likely to have been genetic e s o

R than environmental. a l e The fort, overlooking the River Nile m a

P between the first and second cataracts (now r D

: located on a headland in Lake Nasser – o t o

h Figure 8.) was built in Phaoronic times (ca. P ( 3,000 years ago) and human activity lasted there until the Ottoman era. Throughout all stages of occupation, the inhabitants successfully grew barley by using the natural water cycle provided by the River Nile (‘basin irrigation’), not via artificial irrigation. The ‘mystery’, if it is one, deepens when one realises that contemporaneous barley remains found downstream of the first cataract (from sites such as Tell al-Amarna, 250 miles north of Luxor) are six-rowed. Why did the people of Qasr Ibrim prefer two- rowed barley, when, if it was primarily for feed purposes, six-rowed forms fit the bill Figure 7: Spikelet morphology from Qasr Ibrim barley: a) unattached spikelet; b) spikelet and better? Was the two-rowed barley used for bract attached to rachis. (fs = fertile spikelet; slb = sterile lateral bract; g = glume; r – rachis. brewing purposes, I wonder? Scale divisions are 1mm.) One of the team, Robin Allaby, was of the opinion that it was unlikely that the ancient Since then, brittle six-rowed barleys have Rose, reported on a two-rowed barley (Figure farmers around Qasr Ibrim willfully decided been recorded from other sites, including 6.) that arose by a different mechanism to that to grow two-rowed barley, because the six- Israel, Cyprus, and Libya. The original in extant barley. The samples, collected from rowed phenotype produces higher grain hypothesis was later rejected on several the Lower Nubian fortress site of Qasr Ibrim, yields, so the reasons behind such selection grounds and there is debate as to whether the had distinctive lateral bracts (Figure 7.) and must be related to local environmental nomen H. agriocrithon is biologically showed a discord between genotype and conditions – such as water stress. As he tenable. Many workers contend that H. phenotype. explained: “Qasr Ibrim is located in the upper agriocrithon originated as the result of a All the barley recovered here (from Nile which is very arid in relation to the natural hybridisation between H. spontaneum whatever level of occupation) was genetically lower Nile where six-row remains are found and six-rowed barley that occurred in consistent with the six-row condition, but and we know from previous studies that two- northern parts of Afghanistan, Pakistan or with a two-row phenoty pe! This was row barley can tolerate water stress better India and that seeds of their segregants demonstrated when DNA was extracted from than the six-row variety.” became mixed into barley or wheat samples samples and the Vrs1 gene amplified. which were brought up to Tibet. Further work Surprisingly, the team found that the barley at The barley genome has shown that the Himalayas can be Qasr Ibrim carried the non-functional Vrs1 With 5.3 billion letters of genetic code, or considered a region of domesticated barley allele, and was, therefore, derived from a six- 5,300 million base pairs (Mbp), the barley diversification and that a genetic modification rowed ancestor. genome is one of the largest found in cereal occurred during the migration of barley from A switch from six- to two-row would have crops and almost twice the size of the human the Near East to south Asia. necessitated extreme selective pressure in genome. It is slightly smaller than the three favour of the latter condition and the individual genomes in hexaploid wheat and Qasr Ibrim: another anomaly? consistency of the two-row phenotype some 40% smaller than that of rye. As with A couple of years ago, Egyptian Exploration throughout all of the various levels of other plant species with medium to large Society archaeologists, led by Dr Pamela occupation over three millennia indicates that genomes, the vast bulk of the DNA in barley )

. is represented by repetitive DNA sequence S E

E motifs, typically 2 to 10,000 bp long, that are , e s

o repeated hundreds, or even thousands, of R a l times in the genome. e m a In the main scheme of things, the cereals P r

D have been evolving independently from a : o t common ancestral species for 50 –70 million o h P

( years, but despite this long period of independent evolution, cereal genes and genomes display high conservation, and comparisons of the physical and genetic maps of the grass genomes show conservation of gene order and orientation (which is called ‘synteny’). I

I The author can supply an extensive list of references. You can contact Ian on: Figure 8. Qasr Ibrim as it is now – partially flooded. [email protected]

44 Brewer & Distiller International • December 2010 • www.ibd.org.uk