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 the swollen shoot disease of cacao in Ghana. Each of these species consists of a multiplicity of strains. The New Juaben strain, the most virulent cacao swollen shoot virus 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 cacao swollen shoot 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.

Cacao swollen shoot disease (CSSD) caused by complexes of cacao swollen shoot badnaviruses (family Caulimoviridae, genus Badnavirus) remains highly prevalent and devastating in West Africa. The disease continues to impact substantially on cacao yield loss, cacao tree mortality, and decline in foreign exchange income from cacao bean sales. Currently, the disease is estimated to have a prevalence rate of over 30% in Ghana, as assessed in the ongoing third country-wide surveillance program. Although achievements from past research interventions have greatly elucidated the etiology, biology, epidemiology, diagnostics, and management of the disease, there are some outstanding knowledge gaps. The role of these information gaps and their effect on CSSD epidemiology and prevalence remain unanswered. This paper summarizes existing scientific knowledge from past research achievements that have provided elucidation on CSSD epidemiology, management options, and guided future research. The discussion highlights the need for multidisciplinary research with modern tools and institutional collaborators to holistically bring clarity on knowledge gaps on pathogen biology, virus–host-–vector interactions, role of environmental and soil nutrient effects on CSSD severity, evolution pattern, role of alternative hosts on virus species diversity, vector population dynamics, and their overall impact on CSSD prevalence and integrated management in cacao plantations.

The cacao swollen shoot disease (CSSD) caused by a complex of badnavirus species presents a major challenge for cacao production in West Africa, especially Ghana and Côte d’Ivoire. In this study, CSSD species detection efficiency, diversity, and geographic distribution patterns in cacao plantations in Ghana and Côte d’Ivoire were investigated through field surveillance, PCR detection assays, sequencing of positive amplicons, and phylogeographic clustering. Cumulatively, the detection efficiency of the tested CSSD primer sets that were targeting the movement protein domain of the virus ranged from 0.15% (CSSD-3 primer) to 66.91% (CSSD-1 primer) on all the symptomatic cacao leaf samples assessed. The identified CSSD species differed phylogenetically and overlapped in distribution, with the cacao swollen shoot Togo B virus (CSSTBV) (n = 588 sequences) being the most prevalent and widely distributed compared to the other CSSD species that were encountered in both countries. Geographically, the cacao swollen shoot CE virus (CSSCEV) species (n = 124 sequences) that was identified was largely restricted to the bordering regions of Ghana and Côte d’Ivoire. These results provide updated knowledge of the geographic distribution of the key CSSD species and their diagnostic efficiency and, thus, provide guidance in identifying locations for structured testing of cacao germplasm and optimal diagnostics for the predominant CSSD species in Ghana and Côte d’Ivoire.