Barley heads east: Genetic analyses reveal routes of spread through diverse Eurasian landscapes

Abstract

One of the world’s most important crops, barley, was domesticated in the Near East around 11,000 years ago. Barley is a highly resilient crop, able to grown in varied and marginal environments, such as in regions of high altitude and latitude. Archaeobotanical evidence shows that barley had spread throughout Eurasia by 2,000 BC. To further elucidate the routes by which barley cultivation was spread through Eurasia, simple sequence repeat (SSR) analysis was used to determine genetic diversity and population structure in three extant 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.). Analysis of data using the Bayesian clustering algorithm InStruct suggests a model with three ancestral genepools, which captures a major split in the data, with substantial additional resolution provided under a model with eight genepools. Our results indicate that H. vulgare subsp. vulgare f. agriocrithon accessions and Tibetan Plateau H. vulgare subsp. spontaneum are closely related to the H. vulgare subsp. vulgare in their vicinity, and are therefore likely to be feral derivatives of H. vulgare subsp. vulgare. Under the eight genepool model, cultivated barley is split into six ancestral genepools, each of which has a distinct distribution through Eurasia, along with distinct morphological features and flowering time phenotypes. The distribution of these genepools and their phenotypic characteristics is discussed together with archaeological evidence for the spread of barley eastwards across Eurasia.

Early integration of pastoralism and millet cultivation in Bronze Age Eurasia

“…For Early Bronze Age pastoralists in the IAMC, however, millet would have been initially perceived as an attractive fodder resource offering hardy and versatile properties, especially compared to wheat and barley, which might have already been locally cultivated. The subsequent decline in millet foddering during the Late Bronze Age is likely due to C 3 cultigens arriving via secondary crop dispersals [5], especially landraces of barley adapted to high altitudes [66]. From ca 1750–1000 cal BC, this diversification in cropping across Asia is also linked to reducing risks during climatic shifts towards cooler conditions [25].…”

From ecological opportunism to multi-cropping: Mapping food globalisation in prehistory

“…More substantial movements of wheat and barley took place after 2000 BC across land (Liu et al, 2016a). The spreads of free threshing wheat and naked barley into China appear to be distinct in both space and time (Liu et al, 2017a), via several possible different routes (Lister et al, 2018). These crops appeared in central China during the second and the first millennium BC, respectively (though note the early dates of wheat in eastern province of Shandong discussed above) (Liu et al, 2017a).…”

Archaeobotanical investigations at the earliest horse herder site of Botai in Kazakhstan

“…The timing, means, and pathways of pioneer crop dispersal across Eurasia have attracted scholarly interest for some time. Recent studies suggest that wheat reached China following possibly steppe route by 3000 BC (Long et al 2018), while barley reached China via multiple routes by 2000 BC (Lister et al 2018;Liu et al 2017). At a similar time, the Chinese domesticate broomcorn millet reached Europe (Motuzaite Matuzeviciute et al 2013a;Liu et al 2018).…”

“…No artefacts clearly attributed to crop processing or cultivation have yet been identified at Botai culture sites. From the west to east, recent studies have clarified the chronology of crop movements and proposed that the eastern dispersals of wheat and barley might have been distinct in time and space (Lister et al 2018;Liu et al 2017;Liu et al 2016). From the east to west, it has been argued that the arrival of the domesticated horse in southeast Europe coincides with the earliest arrival of Chinese millet, both of which could have spread via the steppe corridor (Valamoti 2013).…”