Genetic Roots of Cacao Trees Traced By
Dennis O'Brien December 3, 2008
By examining the DNA of cacao trees,
Agricultural Research Service (ARS)
scientists and colleagues from confectionery giant
Mars, Inc., have traced the
genetic roots of the key ingredient in chocolate.
Cocoa comes from the Theobroma cacao tree, which
forms the basis of a multibillion-dollar U.S. chocolate industry. The seeds are
processed into cocoa beans that are the source of cocoa, cocoa butter and
chocolate. But diseases cost growers an estimated $700 million each year, and
scientists have been looking for ways to produce cacao trees that can resist
Kuhn, a molecular biologist at the ARS
Horticulture Research Station in Miami, Fla., and the research team
published findings this fall that are a step toward that goal, shedding light
on Theobroma’s genetic diversity.
extracted DNA from the leaves of 952 cacao trees maintained in germplasm
collections in Miami, Puerto Rico, Ecuador, Costa Rica, Trinidad and Brazil.
The trees were collected by plant explorers over the past 70 years and came
from 12 South American countries.
By looking at patterns among 106
genetic markers, the researchers were able to pinpoint where cacao has the
greatest genetic diversity and where it likely originated: the upper Amazon
basin of Peru.
The researchers also found enough genetic diversity to
realign what might be considered Theobroma’s family tree,
breaking it up into 10 major genetic groups, instead of the commonly accepted
Kuhn hopes the findings will encourage breeders to increase the
diversity of their cacao tree stocks by crossbreeding among the 10 groups. That
would reduce outbreaks of diseases that penetrate tree fruit, destroy
seed-bearing pods and can cause farmers to lose up to 80 percent of their crop.
Breeders should think about using the entire palette of genetic diversity to
improve cacao breeding programs and avoid certain diseases such as black pod
and witches' broom, according to Kuhn.
The research was published recently in the online, peer-reviewed
journal PLoS One.
is a scientific research agency of the U.S.
Department of Agriculture.