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Cacao: yesterday, today and tomorrow
Cocoa pods ready for harvest in cocoa plantation. Photo: IITA
A detailed study of the genetic diversity of almost 1000 cacao trees (Theobroma spp) has identified the most likely places where the crop survived the most recent Ice Age and pinpointed a region that should be protected now to conserve cacao diversity to meet future challenges.
Field genebanks of cacao contain hundreds of accessions along with geographical data on the origin of those trees. Dr Evert Thomas, a Belgian Associate Expert based at Bioversity International’s office in Cali, Colombia, and colleagues examined previously-published DNA profiles from the trees and identified 10 groups of individuals, or clusters, that share genetic similarities. Looking where those clusters come from reveals that Amazonian Ecuador and a bean-shaped area encompassing the border between Brazil and Peru and the southern part of the Colombian-Brazilian border harbour the greatest genetic diversity. Representatives of five of the clusters were collected in this area. No other area contained as many clusters.
This area is also identified by climate models as one of the places where, 21,000 years ago, at the peak of the most recent Ice Age, conditions were relatively favourable for cacao. People arrived in the Amazon around 11,200 years ago, and started to domesticate and manage cacao for the pulp around the beans, which was still being eaten as a snack and fermented into an alcoholic drink by local people when Europeans arrived in the early 16th century.
Domestication for cocoa beans, the source of chocolate, probably took place in Central America around 4000 years ago, but Thomas’ analysis suggests that southern Peru may be the post-Ice Age centre of origin and source of Meso-american cacao.
“From there, humans brought it to Central America,” he says. “But we cannot tell for sure whether it came up the Pacific coast to Mexico – after crossing the Andes in Ecuador – or travelled up the eastern side of the Andes.” Current evidence slightly favours the eastern route. A new method by one of Thomas’ co-authors may help to settle the question.
Map illustrating the bean-shaped highly diverse cacao area in Latin America.
Either way, the cacao trees of present-day Central America experience more seasonal variation in temperature and rainfall than those elsewhere. Although Thomas does not say so in the paper, this might make them good candidates as raw material for future breeding efforts to meet the challenges of climate change. However, projecting climate models forward to 2050 shows that many of the cacao areas in Central America will become unsuitable for the crop. In Latin America too, the area suitable for cacao shrinks, especially in the high-diversity bean-shaped area. That could be a threat to the survival of cacao diversity, although many places within the bean-shaped area currently enjoy some level of conservation protection. One that does not is the area around the town of Iquitos in Peru, which harbours high levels of genetic diversity and the greatest number of genetically different clusters. So could these results add to the impetus for a protected area there?
“That was not the intention of this study,” Thomas said. “We didn’t look at that specifically. But the area does also have the highest species richness of trees in Amazonia.” The climate model suggests less change in this area, meaning that target species protected in this area would be reasonably safe against changing weather patterns.
The study also identifies areas that should be explored now for additional cacao diversity: places where cacao has survived since the depths of the last Ice Age and where there is already good evidence of genetic diversity. The Madre de Dios department of Peru is one place that would be worth exploring, the authors of the paper say. However, they also caution that before launching new collecting expeditions, scientists need a better understanding of what is already present in cacao field genebanks, and that conservation on farm and in situ needs to be beefed up, too.
The full study is available in the open-access journal PLOS One here.
 | Bioversity International is a member of the CGIAR consortium |
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This work by Bioversity International is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. |
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