Nucleotide sequence evidence for three distinct sugarcane streak mastreviruses

The complete sequences of four clones of sugarcane streak virus (SSV) isola tes from Egypt and one SSV clone from Reunion island were determined. The f our Egyptian genomes were highly similar to one another (97-99% nt identity ) and were considered as variants of the same virus. The Egyptian SSV was g enetically different from all other mastreviruses, the closest virus being SSV from South-Africa (60% nt identity), and defined as a new mastrevirus s pecies named SSEV. The SSV clone from Reunion was highly related to the SSV from Mauritius and SSV from Nigeria, for which only partial sequences were available, indicating that the three sugarcane streak isolates from Maurit ius, Reunion and Nigeria were strains of the same virus tentatively named S SMV. This work further confirms that SSMV is a distinct viral species compa red to other mastreviruses, including the SSEV (59% nt identity) and SSV (6 6% nt identity). By comparing two clones from the Mascarene islands, we cor related substitutions in the C-terminal end of the coat protein with a diff erent response to a monoclonal antibody, providing data on the mapping of a specific epitope. Agroinoculations experiments demonstrated that an SSEV c lone induced more severe symptoms on maize than two clones from the Mascare ne. Inside the African streak virus cluster, the sugarcane mastrevirus isol ates were gathered in a sub-cluster of three viruses, SSEV, SSV and SSMV. T he diversity of the SSVs is discussed in relation to its hose, sugarcane, a n imported crop in Africa.