Caroline Roullier, Laure Benoit, Doyle B. McKey, and Vincent Lebot (2013). Historical collections reveal patterns of diffusion of sweet potato in Oceania obscured by modern plant movements and recombination, PNAS DOI: 10.1073/pnas.1211049110
22/02/2013 - Article
The Europeans may not have been the first foreigners to set foot in the Americas. Several centuries before them, Polynesian ships apparently landed on the coast of Peru, and eventually sailed home with sweet potatoes, which are now found throughout the Pacific. This has been confirmed by a vast study by a team of scientists from the CNRS and CIRAD, published on 23 January in Proceedings of the National Academy of Sciences .
The sweet potatoes eaten in Oceania indeed originated in the Americas. Better still: the tuber was apparently brought back from South America on Polynesian ships, several centuries before the first European expeditions. It was the genetics of the plants grown today that shed new light on this part of human history. "The tuber, which is now grown throughout the Pacific, was described by the first European explorers. This has been confirmed by archaeological finds in Hawaii, the Cook Islands and New Zealand, dated to between 1000 and 1400 AD ," Caroline Roullier, a PhD student in evolutionary biology who wrote the article published in PNAS, explains. "The question I set out to answer was: how did they get there? ".
Several elements suggest that sweet potatoes spread from the Americas to Oceania. Firstly, it is in South America that the oldest archaeological remains have been found, some of which could be up to 10 000 years old. There are also intriguing linguistic factors: throughout Polynesia, sweet potato is called kumara… and that is the Quechua name given to it in Peru and Ecuador!
To confirm this hypothesis, Caroline Roullier, who was writing her thesis in Montpellier (at the Centre d’écologie fonctionnelle et évolutive/CNRS and CIRAD), did several thousand genetic analyses. A Herculean task given that the species has not one, but three pairs of each chromosome, ie six copies of each gene! "First of all, we had to analyse the genetic diversity of varieties from tropical America, where the plant came from. We found two distinct groups, corresponding to plants from the Peru-Ecuador region and others from Central America and the Caribbean. We then compared them with the genetic signature of the forms found in Oceania, in other words 1200 living plants and 60 samples from Captain Cook's herbaria ."
The result was unequivocal: yes, the kumara from Peru is indeed the ancestor of Polynesian sweet potatoes. It was analyses of the 18th-century herbaria that confirmed this, since subsequent introductions of sweet potato plants, imported into the Pacific in the 16th century by the Portuguese (from the Caribbean) and the Spanish (from Mexico) recombined with the first kumaras, gradually covering the tracks of the first journeys.
Sunday 24 February
from 3 pm onwards on the CIRAD stand
(Hall 4, Aisle C, Stand 100, Porte de Versailles Exhibition Centre, Paris)
Conference: Enquête sur les origines étonnantes de la patate douce (Study of the surprising origins of sweet potatoes)