Résumé
Characteristic symptoms of Tomato yellow leaf curl disease on tomato plants with a great economic impact were recently observed in several islands of the South West part of the Indian Ocean. Tomato leaf samples presenting symptoms were assessed for viral presence by degenerate begomoviruses primers. Samples from Madagascar, Mayotte and Réunion were tested positive for DNA-A. No presence of DNA-B or DNA-? was revealed. For Réunion, the complete DNA-A was cloned and sequenced. Agroinoculation of tomato plants and transmission by Bemisia tabaci confirmed the Koch's postulate. The most significant alignments were obtained with Tomato yellow leaf curl virus (TYLCV) isolates with 98 to 99% nucleotide identity (DNAMAN, Lynnon Corporation, Quebec), suggesting that the virus present in Réunion is an isolate of TYLCV. For Madagascar, the 522 bp of the core region of the capsid protein (Whyatt and Brown, 1994) showed the most significant alignments with begomoviruses (NCBI, BLAST), 86 to 88% nucleotide identity (DNAMAN) with the isolates from Mayotte, 82% nucleotide identity with TYLCV isolates, South African mosaic virus - M12 (SACMV-[M12]) and East African mosaic Malawi virus - Malawi [K]. For Mayotte, the same region of the capsid protein showed similarly the most nucleotide identity with the isolate from Madagascar (86 to 88%), 86 to 87% nucleotide identity with TYLCV isolates and 85 to 86% nucleotide identity with SACMV-[M12]. The low nucleotide identity of begomovirus isolates from Madagascar and Mayotte (< 89%) with available begomovirus nucleotide sequences suggest the presence of two new species. To perform our analysis, the cloning and sequencing of the complete DNA-A of these viruses is actually in course. (Texte intégral)