Cacao Frosty Pod! Sounds like the name of a new breakfast cereal. Hidden behind this misleading, cheerful name is a nasty disease of cacao plants that – together with its sister species Witches Broom – is destroying cacao plantations in South America and seriously threatening our demand for the most delicious chocolate.
How to make chocolate from cacao trees
Let’s first have a look at the origin of our chocolate. A few years ago, I have been working as a guide in the Palmengarten – Germany’s biggest botanical garden – in Frankfurt/Main. One of my favorite plants to show was Theobroma cacao – the cacao tree. It is surprising how few school kids know that chocolate is not growing as a chocolate bar on a tree.
Chocolate is made from cacao beans that are produced inside massive fleshy pods that stick out from the stem and branches of the evergreen cacao tree. After harvest, the beans are removed from the pods and set in a wooden box for fermentation. During the fermentation process, a soup of yeast and bacteria enhances the chocolate flavor and reduces the bitterness. After drying the fermented beans, grinding and adding milk and sugar, the cacao beans have been promoted to a bitter sweet symphony of chocolate flavors.
Where is cacao grown?
Cacao is grown in the hot and humid tropical regions around the Equator. Two-third of the world’s cacao is produced in only four West-African countries: Ivory Coast, Ghana, Nigeria and Cameroon. Ivory Coast and Ghana dominate cacao production: together they cultivate half of the world’s cacao. Now you might wonder: If most of the cacao is produced in West-Africa, why should we worry about a fungus attacking the cacao trees in South America?
South America is home to the finest chocolate variety
The reason is the following: The cacao grown in West-Africa is mainly the Forastero variety – also called bulk cacao – that is used for manufacturing mass-market chocolate. In South America, the Criollo and Trinitario varieties provide the delicious and delicate “fine grade” cacao beans. Only 5% of the world’s cacao beans are considered “fine grade. Ecuador is the world’s largest producer of “fine grade” beans, followed by Venezuela, Panama and Mexico.
Evil chocolate sister – Witches Broom
In the early 19th century, Ecuador was one of the biggest chocolate suppliers. Over 30% of the world’s cacao was produced in Ecuador allowing the “Cacao kings” living north of the capital of Guayaquil extravagant lifestyles. Their excesses were abruptly ended in 1921 when Witches Broom eradicated the Ecuadorian cacao crop.
Witches Broom refers to a deformity of the leaf-bearing branches and stem-borne cacao flowers, which result in a dense mass of swollen branches tipped with bunches of stunted leaves – the brooms. The stalks that support the cacao pods become thickened and the entire fruit is distorted. Witches Broom is caused by the fungus Moniliophthora perniciosa – a mushroom-forming fungus. Mushrooms are the sexual fruiting bodies of this class of fungi. The mushrooms appear on the cacao broom when it has dried out and they produce millions of basidiospores that are blown by the wind to neighboring cacao trees.
Frosty Pod – the really evil chocolate sister
Frosty Pod Disease is caused by the Witches Broom’s sister species – Moniliophthora roreri. Frosty Pod is like a crippled, but more aggressive version of Witches Broom. No mushroom formation or any other sexual fruiting body has ever been observed for the Frosty Pod fungus.
(Maybe it’s the lack of sex that explains its crave for chocolate.). It is named after a layer of white mycelium that develops on dark, chocolate-colored spots on the cacao pods. These dark spots appear 40-80 days after the fungal spores has germinated on the pod and penetrated the pod epidermis. During this asymptomatic stage, Frosty Pod causes internal damage to the pod and beans. One week after the appearance of the dark spots, the characteristic white powder appears on the pod surface. After ca. three month, the fruits become dry and remain mummified on the cacao trees trunk, where they serve as mass producers of spores (over 7 billion per fruit!) that cause waves of infection over a long period of time.
Frosty Pod Rot is found in all north-western countries in South America. It is more destructive than black pod (a cacao disease in West Africa) and more dangerous and difficult to control than witches broom. In affected countries from Panama to Mexico the yield losses can be higher than 80% and Frosty Pod is the main yield-limiting factor.
Sources: Aime et al. , Mycologica, 2005, International Cacao Industry (http://www.icco.org/about-cocoa/pest-a-diseases.html), Makechocolatefair.org, “Cacao Diseases: Important Threats to Chocolate Production Worldwide” Myths and Misnomers, Harry C. Evans, CAB International, Egham, Surrey, UK