Résumé
CIRAD's sugarcane quarantine imports sugarcane varieties from different countries all over the world. These varieties, imported as cuttings or tissue-cultured plantlets, are likely to harbour pathogenic organisms and especially viruses. Among the 10 virus species that have or might have been introduced into CIRAD's quarantine, Sugarcane mosaic virus (SCMV), Sorghum mosaic virus (SrMV), Sugarcane streak mosaic virus (SCSMV) and Sugarcane yellow leaf virus (SCYLV) are the most liable to be spread outside the quarantine glasshouses. The risk of spread is due to the presence of insect vectors (in particular aphids such as Rhopalosiphum maydis) in the Mediterranean area and a large variety of weeds (mainly Gramineae) that are listed as alternate host plants of these viruses. Eighty-seven leaf samples (4 from maize, 10 from Johnson grass, 72 from sorghum and 1 from Setaria adhaerens) were collected in the neighbourhood of CIRAD's quarantine and tested for viruses using RT-PCR and RFLP techniques. Almost all samples showed mosaic symptoms and 86 were infected by Maize dwarf mosaic virus (MDMV) (SrMV-SCH cannot be excluded) and/or SCMV belonging to the monophyletic maize group. None of these viruses was likely to come from CIRAD's quarantine glasshouses. Neither SCMV belonging to the sugarcane group nor SCSMV was detected. A virus related to (but different from) SCYLV was detected in two Johnson grass samples, but its identity and origin have not been investigated yet. (Texte intégral)