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 as proposed by Chessman in 1944 
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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