About 50% of the world’s chocolate comes from cacao trees in the West Africa countries of Ivory Coast and Ghana. The devastating news coming from there is that a quickly spreading virus threatens the health of the cacao tree and the dried seeds from which chocolate is made, jeopardizing the global supply of the world’s most popular treat.
The damaging pathogen is attacking cacao trees in Ghana, resulting in harvest losses of between 15% and 50%. Spread by small insects called mealybugs (Pseudococcidae, Homoptera) that eat the buds, flowers, and leaves, the cacao swollen shoot virus disease (CSSVD) is among the most damaging threats to the root ingredient of chocolate.
CSSVD was first observed in the eastern region of Ghana in 1936 by a farmer and its virus nature was confirmed in 1939, but in recent years, it has proliferated.
“This virus is a real threat to the global supply of chocolate,” said mathematics Prof. Benito Chen-Charpentier of the University of Texas at Arlington and an author of the study in the journal PLOS One under the title “Cacao sustainability: The case of cacao swollen-shoot virus co-infection.”
Globalization as a root cause
A recent increase in the spread of plant pests and diseases is caused by globalization, climate change, agricultural intensification, and reduced resilience in production systems. A vast number of plant pathogens pose a serious threat to food safety and security, national economies, biodiversity, and rural environment, he said.
“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,” he warned.
Farmers can combat the mealybugs by giving vaccines to the trees to inoculate them from the virus – but the vaccines are expensive, especially for low-wage farmers, and vaccinated trees produce a smaller harvest of cacao, thus compounding the devastation of the virus.
Chen-Charpentier and colleagues from the University of Kansas, Prairie View A&M, the University of South Florida, and the Cocoa Research Institute of Ghana have developed a new strategy: using mathematical data to determine how far apart farmers can plant vaccinated trees to prevent mealybugs from jumping from one tree to another and spreading the virus.
“These insects have several ways of movement, including moving from canopy to canopy, being carried by ants, or blown by the wind,” Chen-Charpentier explained “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.”
By experimenting with mathematical patterning techniques, the team created two different types of models that allow farmers to create a protective layer of vaccinated cacao trees around unvaccinated trees.
“While still experimental, these models are exciting because they would help farmers protect their crops while helping them achieve a better harvest,” Chen-Charpentier said. “This is good for the farmers’ bottom."