Résumé
Cultivated yams (Dioscorea spp.) are propagated vegetatively through their tubers, which results in the accumulation of tuber-borne virus infections, and their perpetuation from one crop to the next. These infections reduce the productivity of the plants and are an impediment to the international movement and exchange of yam germplasm. The only effective method of controlling these virus diseases is to use virus-free planting material. The 26 virus species that have been reported to infect yams worldwide fall into nine taxonomic genera, but only three of these (Badnavirus, Potyvirus and Cucumovirus) have been shown to be widespread in recent surveys across West Africa. Badnaviruses were detected in over 95% of landraces and breeding lines suggesting its wide distribution in West Africa. Analysis of >150 partial PCR-amplified badnavirus RT-RNaseH sequences has grouped them into 12 species clusters each sharing <80% nucleotide identity to each other. As such species differences were not identifiable from their single RT-RNaseH PCR products, denaturing gradient gel electrophoresis (DGGE) was evaluated for its usefulness to discriminate these sequences. Seventeen RT-RNaseH PCR products from West African yam breeding lines produced 11 discrete DGGE bands that represented sequence variants. DGGE was found to be a successful technique for rapid identification of the true diversity of yam badnavirus sequences in a given sample. The existence of badnavirus PCR-positive, but ISEM/ELISA negative results indicated that some breeding lines and landraces contain integrated badnavirus sequences, and this has been supported by nucleic acid hybridization studies. Future research is on-going to determine which of these sequences represent dead integrants, and which are activatable sequences that will pose a serious threat to yam germplasm health and movement. (Texte intégral)