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Researchers analyzing the genomes of cocoa trees traced their origins to a "single event of domestication" about 3,600 years ago. The discovery opens a new front in a long debate about when and where humans began to grow the chocolate source.
"This evidence allows us to better understand how human beings have moved and settled in America," said Omar Cornejo, population geneticist at Washington State University and lead author of an article on the subject. ;study Biology of communication, an open access journal for nature publishers. "It's important in itself, because it gives us time to ask questions that may be more delicate: how long did it take to make a good cocoa?" What was the strength of the process? domestication? How many plants were needed to domesticate a tree? "
The study, which involved 18 scientists from 11 different institutions, also revealed that cocoa domestication ended up selecting taste, disease resistance and theobromine stimulant. However, this has been done at the cost of preserving genes that have reduced crop yields.
The researchers sequenced the genome of Theobroma cacao in 2010. This book describes what Cornejo calls an archetype of the cocoa genome, while this study, by sequencing 200 plants, allows to identify the variations of the genome likely to reveal its evolution.
The researchers examined "the prince of cocoas", the Criollo, a rare, tasty wine and the first to be domesticated. They discovered that it had been domesticated in Central America 3,600 years ago, but that it came from the Amazon Basin, near the present border between southern Colombia and the northern part of the country. Ecuador, from an ancient germplasm known as Curaray. Chances are it's been introduced in Central America by traders, said Cornejo.
The population of the tree at the time comprised between 437 and 2,674 individual trees, and most likely about 738 trees. The period of domestication 3,600 years ago, with margins of 2,481 and 10,903 years, corresponds to traces of theobromine found in Olmec pottery and to large-scale analyzes of ancient and modern human DNA that located colonization in the Americas about 13,000 years ago.
The researchers also supported the idea that domestication would be costly, as producers who choose plants with desirable traits can eventually create plants that accumulate counterproductive genes – "deleterious mutations" – by making them less fit.
The findings of the study could help identify the genes that cause specific traits that breeders can focus on, including yield.
"What we wish for is a way to associate plants of high productivity populations – like Iquitos – with plants of Criollo origin, while retaining all those desirable traits that make Criollo cocoa the best in the world, "said Cornejo.
Cornejo worked on the study at WSU, where he used the high-performance computing power of the Center for Institutional Research Computing for analysis, and at Stanford University, where he was a postdoctoral fellow in Carlos Bustamante's laboratory. . the author on the paper where the data sequence was made. Funding for the research was provided by Mars, Incorporated, which has made considerable efforts to sequence and study the cocoa genome.
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More information:
Omar E. Cornejo et al., Genomic population analyzes of chocolate maker Theobroma cacao L. provide information on its domestication process, Biology of communication (2018). DOI: 10.1038 / s42003-018-0168-6
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