Next Generation Sequencing elucidates cacao badnavirus diversity and reveals the existence of nine viral species associated with cacao swollen shoot disease. [P.46]

Cacao swollen shoot virus (CSSV) is a member of the family Caulimoviridae, genus Badnavirus and is naturally transmitted to Theobroma cacao by several mealybug species. The virus is restricted to West Africa, while the cacao tree originates from the Americas, and has therefore most probably an indigenous origin on the West African subcontinent. The resultant disease has caused enormous economic damage in Ghana since the 1930's but was 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 yield losses and tree death. CSSV populations in West African countries are genetically structured into several different groups according to the diversity in the first part of ORF3 corresponding to the movement protein. To unravel the extent of isolate diversity we used Illumina HiSeq technology and reconstructed 22 new complete genomes corresponding to the different groups of CSSV sequences. In this way we were able to compare the partial sequences of the RTase region (recognised as the taxonomical region by ICTV using a 20% threshold of nucleotide divergence to denote separate species), and thereby identifying nine different CSSV species. These results will now be used to improve the detection of all badnaviruses present in cacao leaf samples, a vital tool in efforts to halt the spread of the disease and confirm the healthy status of new plantations.