Deadly virus threatens global chocolate supply

The cacao swollen shoot virus disease (CSSVD) is wreaking havoc on cacao trees in Ghana, posing a serious threat to the world’s chocolate supply. Approximately half of the global chocolate production originates from West Africa, particularly Ivory Coast and Ghana. 

The spread of CSSVD, primarily transmitted by mealybugs that feed on the leaves, buds, and flowers of cacao trees, has resulted in substantial harvest losses, ranging from 15% to 50% in affected areas.

Millions of cacao trees lost to the virus

“This virus is a real threat to the global supply of chocolate,” said Benito Chen-Charpentier, a professor of mathematics at the University of Texas at Arlington. “Pesticides don’t work well against mealybugs, leaving farmers to try to prevent the spread of the disease by cutting out infected trees and breeding resistant trees. But despite these efforts, Ghana has lost more than 254 million cacao trees in recent years.”

The economic impact is further compounded for farmers by the high cost of vaccines for the trees, which are not only expensive but also lead to a reduced yield of cacao, exacerbating the challenges posed by the virus.

New strategy against chocolate tree virus

In response to this crisis, Chen-Charpentier has collaborated with researchers from the University of Kansas, the University of South Florida, and the Cocoa Research Institute of Ghana to devise a novel strategy. 

The team utilized mathematical modeling to determine optimal spacing for planting vaccinated cacao trees. This spacing is critical to prevent mealybugs from transferring the virus between vaccinated and unvaccinated trees.

“Mealybugs have several ways of movement, including moving from canopy to canopy, being carried by ants or blown by the wind,” Chen-Charpentier said. “What we needed to do was create a model for cacao growers so they could know how far away they could safely plant vaccinated trees from unvaccinated trees in order to prevent the spread of the virus while keeping costs manageable for these small farmers.”

The team developed two types of mathematical models that enable farmers to create a barrier of vaccinated trees around those that are unvaccinated, potentially offering a new way to manage the spread of CSSVD while maintaining crop yields. 

“While still experimental, these models are exciting because they would help farmers protect their crops while helping them achieve a better harvest. This is good for the farmers’ bottom line, as well as our global addiction to chocolate,” Chan-Charlpetier concluded.

More about cacao trees

Chocolate trees, scientifically known as Theobroma cacao, are the source of all the world’s chocolate. These tropical trees are native to the deep tropical regions of Central and South America, where they thrive in the understory layer of forests, needing a mix of shade and humidity to prosper. 

Growth of cacao trees 

The trees are relatively small, usually not growing beyond 4 to 8 meters in height. They bear fruit called cacao pods, which are large, colorful, and contain the precious cacao beans used in chocolate production. The pods themselves are directly attached to the trunk and larger branches of the tree, a growth pattern known as cauliflory.

Life cycle and challenges

The life cycle of a cacao tree begins with its flowers, which are pollinated by tiny insects. After pollination, the pods take several months to mature, with each pod containing 20 to 60 beans surrounded by a sweet, pulpy matrix. The beans are harvested, fermented, dried, and then processed to make various chocolate products. 

A key challenge for cacao farmers is the tree’s sensitivity to environmental conditions and susceptibility to diseases, which can affect yield and quality of the chocolate products.

Economic and cultural significance 

Historically, cacao has been significant both culturally and economically in the regions where it is grown. It was used by ancient Mesoamerican civilizations like the Aztecs and the Maya not just as food, but also as currency and in religious rituals. 

Today, the global demand for chocolate keeps cacao cultivation economically relevant, though it also presents challenges including the need for sustainable and fair farming practices.

The study is published in the journal PLoS ONE.

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