Historical trade routes for diversification of domesticated chickpea inferred from landrace genomics

According to archaeological records, chickpea (Cicer arietinum) was first domesticated in the Fertile Crescent 10 thousand years ago. Its subsequent diversification in South Asia, Ethiopia, and the Western Mediterranean, however, remains obscure and cannot be resolved using only archeological and historical evidence. In particular, chickpea has two market types: desi, which has a similar flower and seed coat color to chickpeas wild relatives; and kabuli, which has light-colored seed, and is linguistically tied to Central Asia but has an unknown geographic origin. Based on the genetic data from 421 chickpea landraces from six geographic regions, we tested complex historical hypotheses of chickpea migration and admixture on two levels: within and between major regions of cultivation. For the former, we developed popdisp, a Bayesian model of population dispersal from a regional center towards sample locations, and confirmed that chickpea spread within each region along trade routes rather than by simple diffusion. For the latter, migration between regions, we developed another model, migadmi, that evaluates multiple and nested admixture events. Applying this model to desi populations, we found both Indian and Middle Eastern traces in Ethiopian chickpea, suggesting presence of a seaway from South Asia to Ethiopia -- and the cultural legacy of the Queen of Sheba. As for the origin of kabuli chickpeas, we found significant evidence for an origin from Turkey rather than Central Asia.