Publication from the Chocolate Review
by Samantha Madell




Cocoa History

Where is the true home of cocoa?

The debate rages on amongst historians (like Michael Coe) and other chocolate enthusiasts about where exactly the cocoa tree - Theobroma cacao - originated. But most of the people doing this "debating" seem to understand very little about the genetics of agricultural plants, and how much these genes can tell us about a plant's origins.

More than 80 years ago, Nikolai Vavilov (the so-called "Indiana Jones of Botany" and the "father of modern plant genetics") commented on historians who like to debate the origin of plant species. He wrote: "After a detailed study of the centers where the forms of cultivated plants were created, a botanist acquires the right to dispute the conclusions drawn by historians and archaeologists." [1]

From 1916 to 1940, Vavilov undertook an extensive survey of the agricultural plants growing in the Middle East, the Mediterranean, Africa, Asia, Central America, South America, and the Soviet Union. Vavilov was particularly interested in the wild relatives and ancestors of cultivated plants. Over the course of his career as the director of Russia's Institute of Plant Industry, Vavilov built a priceless collection of about 200,000 plant specimens.

During his travels, Vavilov observed that the genetic diversity of crop plants and their relatives tended to be concentrated around particular geographical centres. He theorised that these centres corresponded with the regions where agriculture originated. The centres of diversity that he identified in 1926 are still recognised today. Now they're known as Vavilov Centres, or Vavilov Centres of Diversity. (See the yellow overlays on the maps below, indicating the Mexican and Andean Centres of Diversity, as proposed by Vavilov).

Sadly, Vavilov's brilliant but revolutionary work cost him his life. Vavilov fell foul of Stalin's favourite agronomist, a power-hungry pseudo-scientist by the name of Trofim Lysenko. In 1940, Vavilov was arrested on trumped-up charges of spying and carrying out "wrecking activity in agriculture" [1]. In 1943 Vavilov died in prison from malnutrition: a truly ironic fate for a man whose work brought vast quantities food to the world's people.

As a tragic aside, at least nine of Vavilov's colleagues starved to death during the siege of Leningrad in WWII, while protecting their precious collection of edible plant material, including rice and potatoes [2]. The fact that these scientists valued the plant geneomes that they were protecting more highly than their own lives is truly awe-inspiring.

Where in the world is Theobroma cacao's Centre of Diversity?

Vavilov (mistakenly) believed that the cocoa tree belonged to the Mexican Centre of Diversity (that is, he believed that cocoa had originally evolved in Mexico).

In 1937/38, and in 1942/43, F.J. Pound undertook cocoa-collecting expeditions in the Amazon basin. Pound, an agronomist with the Department of Agriculture in Trinidad, was specifically searching for cocoa trees that showed resistance to the devastating fungal disease known as witches' broom. Pound specifically chose to search the Amazon basin for new cocoa varieties because he was aware of Ecuadorian cocoa trees that had exhibited resistance to witches' broom. On his expeditions, Pound observed the existence of extensive variability in the wild cocoa trees of Ecuador [3]. He also found what he was looking for: "Scavina 6", an Upper Amazon Forastero variety, which remains the best known source of genetic resistance to witches' broom disease.

In 1944, E.E. Cheesman theorised that the cocoa tree was actually native to the Upper Amazon region of South America [4]. Cheesman's theory was based on his awareness of the very high level of variability that Pound had discovered among cocoa populations in the Upper Amazon. In other words, while Cheesman disagreed with Vavilov's specific belief that cocoa had evolved in Mexico, he agreed with Vavilov's basic theory: that the centre of a plant's genetic diversity is synonymous with the plant's genetic origin.

Cheesman believed that cocoa's centre of origin was located in an area with a 400 km-radius, in the vicinity of the rivers Napo, Caquetá, and Putumayo - all tributaries of the Amazon River. (See the circular orange overlay indicating Cheesman's proposed centre of diversity on the maps below).

The idea that the Upper Amazon region of South America is the birth place of cocoa has been supported by science for more than 60 years, not just by the observations of Pound and Cheesman in the 1930s and 40s, but also much more recently by the genetic research of scientists such as Claire Lanaud and Juan-Carlos Motamayor [5].

The most recent research published by Motamayor and his colleagues shows just how genetically diverse the cocoa population of South America is, compared to the genetic poverty of cocoa in Central America [7]. Indeed, Motamayor has proposed a new classification system for cocoa, based on the ten geographical/genetic clusters that his most recent study identified. Motamayor's work shows just how close to the mark Cheesman really was: 70% of Motamayor's genetic clusters are located within the centre of origin that Cheesman proposed more than 60 years ago. And 80% of the clusters are located within the general Andean centre of diversity that Vavilov proposed more than 80 years ago. (See the overlay of Motamayor's cocoa clusters on the second map, below).

Cacao's center of diversity
Cacao's center of diversity as proposed by Chessman in 1944

Overlay of cocoa clusters
Overlay of cocoa clusters by Motomayor 2008


References
1     Mark Popovsky (1984)
"The Vavilov Affair"
Archon Books, Connecticut
2     "A Priceless Collection"
Accessed online in PDF format at: http://food_fiber.okstate.edu/TWELVE.PDF
3     Dias, L.A.S. (2004)
Chapter 3: Origin and distribution of Theobroma cacao L: A new scenario; in "Genetic Improvement of Cacao"
Accessed online at: http://ecoport.org
4     Cheesman, E.E (1944) "Notes on the nomenclature, classification and possible relationships of cocoa populations"
Tropical Agriculture, Vol. 21, pp.144-159
5     Lanaud, C; Motamayor, J-C; Risterucci, A-M (2000)
"Implications of New Insight into the Genetic Structure of Theobroma cacao L. for Breeding Strategies"
Accessed online in PDF format at: http://guiltinanlab.cas.psu.edu/Ingenic
6     Motamayor, J.C.; Risterucci, A.M.; Lopez, P.A.; Ortiz, C.F.; Moreno, A.; Lanaud, C.; (2002)
"Cacao domestication I: the origin of the cacao cultivated by the Mayas"
Heredity Vol. 89, Number 5, pp. 380-386
7     Motamayor, Lachenaud, da Silva e Mota, Loor, Kuhn, Brown, Schnell (2008)
"Geographic and Genetic Population Differentiation of the Amazonian Chocolate Tree (Theobroma cacao L)"
Accessed online at: http://www.plosone.org



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Copyright © 2008 Chocolate Review
Bibliography

Madell, Samantha. "Cocoa History." thechocolatereview.com. 15 Oct. 2008. Web. 15 June 2017.

Published 15 June 2017 LR
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