Chocolate Under Threat from Old and New Cacao Diseases

Theobroma cacao, the source of chocolate, is affected by destructive diseases wherever it is grown. Some diseases are endemic; however, as cacao was disseminated from the Amazon rain forest to new cultivation sites it encountered new pathogens. Two well-established diseases cause the greatest losses: black pod rot, caused by several species of Phytophthora, and witches' broom of cacao, caused by Moniliophthora perniciosa. Phytophthora megakarya causes the severest damage in the main cacao producing countries in West Africa, while P. palmivora causes significant losses globally. M. perniciosa is related to a sister basidiomycete species, M. roreri which causes frosty pod rot. These Moniliophthora species only occur in South and Central America, where they have significantly limited production since the beginnings of cacao cultivation. The basidiomycete Ceratobasidium theobromae causing vascular-streak dieback occurs only in South-East Asia and remains poorly understood. Cacao swollen shoot disease caused by Cacao swollen shoot virus is rapidly spreading in West Africa. This review presents contemporary research on the biology, taxonomy and genomics of what are often new-encounter pathogens, as well as the management of the diseases they cause.