Evolution of Crop Farming III: Barley

by Emma J Devereux

Citation: Devereux, E.J.,(2021), “Barley: Crop Evolutionary History & Future Food Sustainability”, EcoFoodDev, https://www.ecofooddev.com/the-ancient-origins-of-modern-barley/

Barley (Hordeum vulgare) is a principal cereal crop grown worldwide. It is used as a foodstuff, an animal fodder, and in roasting and malting to produce alcoholic beverages such as beer and whiskey. Barley can be sown as a winter or spring crop, with a short growing season. It is the 4^th most important global cereal output after crops such as wheat. It is grown in over 100 countries, with Europe producing around 60% of global barley tonnage. Barley exhibits high adaptability to fluctuating environments, being more tolerant to cold, drought, and poorer soils. In Ireland, Spring Barley is the largest spring crop grown according to Teagasc (Ireland’s Agriculture and Food Development Authority), and is primarily used for feed (87%), with 13% used for roasting and malting.  [cover image: Microscope image of barley seed. Wikicommons]

Barley can be noted as one of the earliest cultivated and domesticated crops and is found on very many archaeological sites. It can thus reveal insights into the emergence of agrarian society, as discussed in the previous post “12,000-year grind: How Climate Change led to Modern Farming”. Barley cultivation has been detected in the Nile River Valley of Egypt from at least 17,000 years ago. The emergence of naked barley (a post-domestication mutation) is thought to have occurred ~8000 years ago in the Middle East, subsequently spreading. Roman gladiators were even known as ‘hordearii’ (‘barley-men’) due to the large amount of barley in their training diet which provided a layer of fat around their mid-section. This allowed for them to be injured for the sake of entertainment, but not fatally wounded. It was not in the interest of investors to lose valuable and successful gladiators, many of whom had a significant fan base and high investment and development costs. Gladiators were expensive to train and good fighters could draw significant crowds, resulting in considerable earnings from games attendance. Therefore, a strict diet was an essential part of their training regime.  

Barley has been associated with beer production and fermentation for centuries. Trace evidence for beer dating back ~9000 years can be found on pottery from archaeological contexts. As mentioned in the previous blog post, evidence for beer production has been found at the Neolithic site of Göbekli Tepe, and large-scale beer brewing is thought to have existed in pre-Dynastic Egypt roughly 7000 to 5000 years ago. Domestic barley has been detected in the Jordan Valley at Gilgal and Netiv Hagdud and dated to 8000-7000 BC. So, barley cultivation and use are much older than most people likely imagine.  

Domestication of barley: the changes that occurred 

Genetic natural selection during cultivation and domestication favoured certain characteristics in barley, depending on the environmental conditions. Understanding the genetic history of cereal crops is beneficial for both sustainable agriculture and in cereal crop breeding programs. 

The name for wild barley is Hordeum spontaneum. H. spontaneum still grows in the Fertile Crescent from Israel and Jordan, to southern Turkey, Iraqi Kurdistan, southwestern Iran, and in Greece, Egypt, Tajikistan and the Himalayas. Wild barley has been found at Natufian period sites (10500BC- 9300BC) such as Hayonim, northern Israel, and Wadi Hammeh, north Jordan. It appears that barley evolved separately at different sites within the Fertile Crescent and journeyed on parallel evolutionary pathways.  

Steps in the evolution of barley from wild to domesticated: 

• By 8000BC, non-brittle rachises had emerged in the cultivated barley population, controlled by two particular genes, Bt1 and Bt2.  
• By 6500BC, 6-row barley emerged, replacing the 2-row form. Farming practices likely selected for this increase in production rates of the barley plant.  
• By 6000BC, further morphological changes occurred, seeing the emergence of a thin-glumed plant- this is the part of the flowering plant which forms the cereal husk.  

These adaptations make it easier to get to the grain, make the plant produce more grain, and make it less likely that the grains will fall from the plant due to disturbance from wind or animal movements etc. Of course, new discoveries, particularly in plant genetics, are being made all the time, adding further details to this picture of evolution.  

As barley is one of the oldest known domesticated crops, it has a wide number of accessions and varieties around the world. It displays high genetic diversity, however, intense breeding programs in modern barley have decreased this diversity (and hence adaptability). An understanding of barley ancestral landraces is important to identify genes for future crop breeding, and also for application in nature-based farm management practices (particularly with regard to the wild relatives of crops which I will discuss in further posts). 

Domestication centres of barley 

As mentioned in the previous post “Crop Cultivation’s Astonishing Age: 10,000 Years of Change”, multiple centres of origin for the domestication of different cereals may exist, the molecular pathways of which are currently being researched. As described in various previous posts, the Fertile Crescent of southwest Asia is a recognized centre of cereal domestication, including for the domestication of barley. From here, genetic evidence combined with botanical evidence from archaeological sites paint a picture of a complicated process of barley domestication, evolving from the brittle-rachised, two-rowed, hulled, wild form travelling on various, parallel evolutionary pathways. The International Barley Genome Sequencing Consortium (IBSC) was established in 2006 to generate a barley genome sequence, and the genome has recently been sequenced and assembled at the chromosome-scale (https://academic.oup.com/dnaresearch/article/27/4/dsaa023/5912017 for more).

Molecular evidence provides detail on the route by which barley cultivation and domestication spread from its centres of origin. Simple sequence repeat (SSR) analysis was used to investigate the genetic diversity and population structure in present and existing barley taxa: domesticated barley (Hordeum vulgare L. subsp. vulgare), wild barley (H. vulgare subsp. spontaneum) and a six-rowed brittle rachis form (H. vulgare subsp. vulgare f. agriocrithon (Åberg) Bowd.). Subsequent computer-based modeling reveals three ancestral gene pools, confirming that cultivated barley spread through Eurasia via several different routes, separated via space and time. 

So now we know that wild barley evolved in different parts of the world, and followed broadly similar pathways to domestication, depending on the different environments. For example, we have barley from the Fertile Crescent, and barley from the Tibetan Plateau. Genetic bottlenecks (a sharp decrease in the size of a population due to environmental events) following domestication will have driven further adaption and change. Wang et al., 2015, undertook a population-based genetic diversity and phylogenetic analysis to investigate the evolution of barley and to explore the effect of genetic diversity in cultivated barley. They looked at grain protein content (GPC) genes to show that the wild barley of Tibet was distinctly different from that of the Near East/Fertile Crescent and confirmed Tibet as a domestication centre for cultivated barley. By comparing haplotype composition of the barley of different regions the authors also saw that the Silk Road may have played a role in the movement of genetic variants of barley between the East and West. 

Though early farmers cultivated multiple crops to mitigate against risk, there is increasing evidence that the hardiness and adaptability of barley may have led to single, crop-dominant, cultivation systems at much earlier periods than previously thought. Lu et al., 2021, describe the site of Bangga (1055-211BC), on the Tibetan Plateau, which provides evidence for high-altitude cultivation of barley as a dominant cereal crop, most likely attributed to its frost tolerant characteristics making it suitable for such high elevations. The authors argue that a niche, barley-dominant, farming system started to develop, due to a combination of social and ecological factors, at least a 1000 years earlier than previously thought (by about 3000 years ago). The environment of the Tibetan plateau is highly variable, and therefore single, staple crop cultivation would have been highly risky for ancient populations. However, it is a testament to the adaptability and resilience of this cereal that not only was it the dominant single crop cultivated, but that a sustainable and powerful society was powered by it.  

There is much more to discover on the origins of barley and the history of production of food. Here are a few links:

• “Yeast Fermentation and the Making of Beer and Wine” https://www.nature.com/scitable/topicpage/yeast-fermentation-and-the-making-of-beer-14372813/ 
• UCL, Early Food Production links https://www.ucl.ac.uk/archaeology/research/directory/early-food-production 
• Archaeology of Food Surplus https://www.tandfonline.com/doi/abs/10.1080/00438243.2017.1294105?casa_token=BoJN7FOiRk0AAAAA:T1kKIuUT1QBXrEPy8A_-v_IV-Z-we-_5MayeJtC6CqCehPE429GJ6BmZaoBX6QmA80pZPh1aiRw 

In upcoming posts, I will discuss the potential of palaeobotanical insights in modern and future cereal farming and the pathways that past vegetative history combined with ecological and genetic research offer towards a sustainable Agri future, starting with an explanation of crop to wild relative research.  

References 

• Dietrich L, Meister J, Dietrich O, Notroff J, Kiep J, Heeb J, et al. (2019) Cereal processing at Early Neolithic Göbekli Tepe, southeastern Turkey. PLoS ONE 14(5): e0215214. https://doi.org/10.1371/journal.pone.0215214  
• Fuller, D., Willcox, G., Allaby, R., 2012,” Early agricultural pathways: moving outside the ‘core area’ hypothesis in Southwest Asia”, Journal of Experimental Botany, pp617-633  
• Garrard, A, 1999, “Charting the Emergence of Cereal Domestication in South-west Asia”, Environmental Archaeology 4, pp67-86.  
• Giraldo, P., Benavente, E., Manzano-Agugliaro, F. and Gimenez, E., 2019. Worldwide research trends on wheat and barley: A bibliometric comparative analysis. Agronomy, 9(7), p.352. 
• Lister, D.L., Jones, H., Oliveira, H.R., Petrie, C.A., Liu, X., Cockram, J., Kneale, C.J., Kovaleva, O. and Jones, M.K., 2018. Barley heads east: Genetic analyses reveal routes of spread through diverse Eurasian landscapes. PloS one, 13(7), p.e0196652. 
• Lu, H., Tang, L., Spengler III, R.N., Boivin, N., Song, J., Wangdue, S., Chen, X., Liu, X. and Zhang, Z., 2021. The transition to a barley-dominant cultivation system in Tibet: First millennium BC archaeobotanical evidence from Bangga. Journal of Anthropological Archaeology, 61, p.101242. 

• Mohammadi, S.A., Sisi, N.A. and Sadeghzadeh, B., 2020. The influence of breeding history, origin and growth type on population structure of barley as revealed by SSR markers. Scientific Reports, 10(1), pp.1-13. 
• Morrell, P.L. and Clegg, M.T., 2007. Genetic evidence for a second domestication of barley (Hordeum vulgare) east of the Fertile Crescent. Proceedings of the national academy of sciences, 104(9), pp.3289-3294. 
• Sato, K., 2020. History and future perspectives of barley genomics. DNA Research, 27(4), p.dsaa023.
• Scanes, C.G., 2018. The Neolithic revolution, animal domestication, and early forms of animal agriculture. In Animals and Human Society (pp. 103-131). Academic Press.  
• Wang, Y., Ren, X., Sun, D. and Sun, G., 2015. Origin of worldwide cultivated barley revealed by NAM-1 gene and grain protein content. Frontiers in plant science, 6, p.803.  
• Weiss, E. and Zohary, D., 2011. The Neolithic Southwest Asian founder crops: their biology and archaeobotany. Current Anthropology, 52(S4), pp. S237-S254. 
• Willcox, G., 2013. The roots of cultivation in southwestern Asia. Science, 341(6141), pp.39-40. 
• Willcox, G. and Stordeur, D., 2012. Large-scale cereal processing before domestication during the tenth millennium cal BC in northern Syria. Antiquity, 86(331), pp.99-114.