Cacao Swollen Shoot Viruses in Ghana

Abstract

Cacao swollen shoot virus causes cacao swollen shoot disease of Theobroma cacao (cacao) plants. At least six cacao-infecting badnavirus species - cacao swollen shoot Togo A virus, Cacao swollen shoot Togo B virus (previously known as Cacao swollen shoot virus), cacao swollen shoot CE virus, Cacao swollen shoot Ghana M virus, Cacao swollen shoot Ghana N virus and Cacao swollen shoot Ghana Q virus - are responsible for this disease in Ghana. Each of these species consists of a multiplicity of strains. The New Juaben strain, the most virulent strain in Ghana, belongs to the Cacao swollen shoot Togo B virus species, and is a commonly used strain in laboratory transmission assays. Infection of cacao trees with multiple strains of the virus is common and new evidence suggests that these coinfections may have resulted in the emergence of recombinant strains of the virus. The impact of these emerging recombinant strains on disease severity is uncertain. This review focuses largely on the discovery of cacao swollen shoot virus in Ghana, diversity of the virus strains, molecular characterization, propagation of virus infection in cacao plants, emergence of recombinant virus strains, vector-mediated transmission of the virus, and the management of the disease in Ghana. It also contains sections on the botany and origin of the cacao tree, its introduction to Ghana, the role of cacao swollen shoot disease in facilitating Ghana’s independence from Britain, and a brief history of chocolate.