Two mild strains of Cocoa swollen shoot virus (CSSV), N1 and SS365B, were assessed for their capability to mitigate the devastating effects of CSSV in field trials at the Cocoa Research Institute of Ghana in comparison with noninoculated cocoa plants. Analysis of growth, mortality, and yield of cocoa trees inoculated with the mild strains over a period of two decades between 1996 and 2014 indicated that the cocoa plants inoculated with mild strains performed significantly (P < 0.05) better in the presence of the severe strains (CSSV 1A) than noninoculated cocoa, albeit degenerated over time. The development of cocoa hybrids studied in the trial showed differences in their performance in the presence of the mild-strain viruses. Spread of the severe virus increased and deteriorated the effects of the mild isolates over time, thereby decreasing the economic life span of the cocoa trees. This observation was consistent in all the trials regardless of the type of mild strain involved. Apparently, the immunity and protection conferred by mild strains of CSSV (SS365B and N1) on cocoa declined over time, and we further confirmed ‘Amelonado’ cocoa to be very susceptible to CSSV infection in terms of effects on growth and yield.

Cacao swollen shoot virus (CSSV), Cacao swollen shoot CD virus (CSSCDV), and Cacao swollen shoot Togo A virus (CSSTAV) cause cacao swollen shoot disease (CSSD) in West Africa. During 2000–2003, leaf and shoot-swelling symptoms and rapid tree death were observed in cacao in Cote d’Ivoire and Ghana. Molecular tests showed positive infection in only ~50–60% of symptomatic trees, suggesting the possible emergence of an unknown badnavirus. The DNA virome was determined from symptomatic cacao samples using Illumina-Hi Seq, and sequence accuracy was verified by Sanger sequencing. The resultant 14, and seven previously known, full-length badnaviral genomic and RT-RNase H sequences were analyzed by pairwise distance analysis to resolve species relationships, and by Maximum likelihood (ML) to reconstruct phylogenetic relationships. The viral coding and non-coding sequences, genome organization, and predicted conserved protein domains (CPDs) were identified and characterized at the species level. The 21 CSSD-badnaviral genomes and RT-RNase H sequences shared 70–100% and 72–100% identity, respectively. The RT-RNase H analysis predicted four species, based on an ≥80% species cutoff. The ML genome sequence tree resolved three well-supported clades, with ≥70% bootstrap, whereas, the RT-RNase H phylogeny was poorly resolved, however, both trees grouped CSSD isolates within one large clade, including the newly discovered Cacao red vein virus (CRVV) proposed species. The genome arrangement of the four species consists of four, five, or six predicted open reading frames (ORFs), and the CPDs have similar architectures. By comparison, two New World cacao-infecting badnaviruses encode four ORFs, and harbor CPDs like the West African species. Three previously recognized West African cacao-infecting badnaviral species were identified, and a fourth, previously unidentified species, CRVV, is described for the first time. The CRVV is a suspect causal agent of the rapid decline phenotype, however Koch’s Postulates have not been proven. To reconcile viral evolutionary with epidemiology considerations, more detailed information about CSSD-genomic variability is essential. Also, the functional basis for the multiple genome arrangements and subtly distinct CPD architectures among cacao-infecting badnaviruses is poorly understood. New knowledge about functional relationships may help explain the diverse symptomatologies observed in affected cacao trees.

A field trial was conducted at the Cocoa Research Institute of Ghana from 1992 to 2004 to investigate the prospects of using Cacao swollen shoot virus (CSSV)-immune crops as a barrier to prevent the spread of the virus from existing outbreaks into newly established cacao plantings. The treatments consisted of four crops—citrus (Citrus spp.), oil palm (Elaeis guineensis Jacq.), kola (Cola nitida Vent.), and cacao (Theobroma cacao L.)—planted as a barrier between cacao trees serving as test plants on one side and as source of CSSV strain 1A infection on the other. Over a 7-year period post CSSV 1A inoculation, the citrus and oil palm barriers were the most effective in protecting test cacao trees from cacao swollen shoot virus disease (CSSVD) spread. The two crops gave comparable results (P = 0.9766) in terms of the cumulative number of visibly infected trees (1 and 5 of 522, respectively). The kola barrier, on the other hand, had a significantly (P < 0.000l) higher number of symptomatic trees (89 of 522) than citrus and oil palm. All three crops (citrus, oil palm, and kola) provided better protection than the control (cacao), which had 134 visibly infected trees out of 522. As shown by economic analyses, growing citrus, oil palm, or kola as barrier crops was as profitable as growing cacao. The implications of the results on the management of CSSVD in Ghana are discussed.

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.