Having sequenced the millet genome, an international consortium involving French researchers from IRD, Indian, Chinese researchers and numerous laboratories from the North and South, studied different wild and cultivated varieties. This allowed them to trace the history of cultivated millet and describe the origin of its adaptation to the world’s driest regions. Its salvation: its renewed genetic diversity when in contact with wild millet.
"Whether it is currently grown in the Sahel, South Africa or India, millet?editor’s note: also known as “pearl millet” or “cattail millet” comes from a single geographical area: Western Sahara, where its cultivation began 4,900 years ago. Under the effect of aridification, it was subsequently pushed southward, from where it spread eastward and westward. It regained genetic diversity, which facilitated its adaptation "1, states Yves Vigouroux, head of the Anthropisation and dynamics of genetic diversity team, within the DIADE unit in Montpellier.
221 sequenced varieties
While the history of millet cultivation as we know it today seems straightforward, “its identification was a complex exercise”, the researcher recognises. To successfully complete their historical research on the cereal which guarantees food security for nearly 100 million people, the researchers began by analysing the entire genome of 221 varieties of cultivated and wild millet from various geographical origins. They subsequently relied on archaeological remains and used an innovative spatial computer model combining geography with genetic analyses in order to determine the likeliest area from where millet started spreading.
Initial genetic analyses indicated a common origin: wild millet of the central Sahel region. More specifically, these cereal populations were previously found in Western Sahara where the climate was more humid than today. This is where millet became domesticated 6,000 years ago, with the selection of key characteristics for its cultivation such as the absence of seed dispersal, before the desertification of the Sahara pushed millet farming southward. As a result, the cereal found its current distribution in the central Sahel region - around Niger and Mali -3,200 years ago, from where it then spread eastward and westward.
According to this logic, as selections relating to plant cultivation result in a loss of genetic diversity, that of cultivated millet should have decreased as it moved away from the central Sahel. However, it was not the case. Among the 5 groups of cultivated millet studied — Eastern, central and Western Sahel, South Africa, India — “we found diversity hot spots in the East in Chad and Sudan, and in the West in Senegal and Mauritania”, points out Yves Vigouroux. In other words, instead of decreasing as it spread geographically, its diversity increased.
To understand this incongruity, the researchers compared the genomes of the cultivated millet from the East and West with those of the wild varieties of the same geographical regions. “We recognised a gene flow [editor’s note: gene transfer] from wild to cultivated millet, adds the researcher. Therefore cultivated millet regained diversity when in contact with their local wild counterpart, which facilitated its adaptation to new growing environments”.
These results finally reconcile archaeologists and geneticists, whose scenarios on the history of millet cultivation diverged up until now, but, more importantly “the next step is to predict the necessary genetic adaptation to future climate, over the next 50 years, thereby supporting the cultivation of these plants”, Yves Vigouroux concludes. In other words, the objective is to give nature a helping hand.
1. C. Burgarella et al. Nature Ecology and Evolution , 6 août 2018, A western Sahara center of domestication inferred from pearl millet genomes , doi : 10.1038/s41559-018-0643-y
Contact : email@example.com