Understanding the origin and spread of the complex of viral species responsible for cocoa swollen shoot disease

Cacao swollen shoot virus (CSSV) is a member of the family Caulimoviridae, genus Badnavirus naturally transmitted to Theobroma cacao by several mealybug species. The virus, restricted to West Africa whereas the cacao tree originates from the Western Hemisphere, could therefore most probably have an indigenous origin on the West African subcontinent. The disease has caused enormous economic damage in Ghana since the1930s but was only restricted to small areas in Togo and Cote d'Ivoire until recently. Now, renewed outbreaks in the main producing areas in Cote d'Ivoire, Ghana and Togo cause serious problems. CSSV populations in West African countries are genetically structured in twelve groups according to the diversity in the first part of ORF3 and the 20% threshold of nucleotide divergence. However, according to ICTV recommendations taking into account the nucleotide diversity in the RTAse region, we could describe seven different species. Based on the geographical dispersal of the different species, we could propose the existence at different times of parallel emergences in each of the West African countries. (Texte integral)