Résumé
In relation to a CIRAD maize breeding project for resistance to virus diseases, maize streak geminivirus (MSV) was thoroughly studied, since it causes the most severe virus disease on maize in Africa. It was shown that MSV belongs to an African Mastrevirus complex including geminivirus isolates causing streaks on wild and cultivated hosts. Based on biological and immunological methods, it appeared that the isolates detected on sugarcane (sugarcane streak virus, SSV) were more variable than those on maize. This was confirmed by molecular studies showing that all the maize isolates belonged to the same species whereas two isolates from sugarcane, a completely sequenced one from Natal (SSV-NAT) and a partially sequenced one from Mauritius (SSV-M), were apparently different. In this study, we obtained further confirmation of the diversity of sugarcane isolates by the characterization of a new species of SSV from Egypt (SSV-EG) distinct from SSV-NAT (60% similarity of the complete genome). A third species originating from the Mascarene archipelago was characterised (SSV-MU) based on the complete sequence of an SSV clone from Reunion which showed high similarity to the SSV from Mauritius (98% in the CP) but below 75% similarity to SSV-EG and SSV-Nat. Interestingly, amastrevirus identified in Nigeria from millet is belonging to SSV-MU. These data indicate that three distinct mastreviruses infect sugarcane in Africa: SSV-MUSSV-NAT and SSV-EG. (Résumé d'auteur)