Molecular characterization of a sadwavirus and a potexvirus infecting yams (Dioscorea spp) in Guadeloupe
Résumé
Yams (Dioscorea sp.) are important food commodities in tropical and subtropical areas of Africa, the Caribbean, South America and the Pacific, where they play a key role in food security. Being vegetatively propagated crops, yams cannot be sanitized via seed production and therefore accumulate viruses over long periods of time. Potexvirus, Carlavirus, Badnavirus, Cucumovirus, Macluravirus and Potyvirus species have been characterized in yams. In addition ESTs (Expressed Sequence Tags) of Dioscorea alata include sequences from families of viruses yet unknown to infect yams, such as Geminiviridae and Secoviridae, showing that the diversity of viral species infecting this crop remains underestimated. This situation has prompted a search for yet uncharacterized viruses infecting yams in Guadeloupe (French West Indies). RT-PCR was performed on crude extracts of symptomatic yams (D. alata, D. trifida), following direct binding of viral particles and using Potexvirus degenerate primers [1]. Several samples gave amplification products, which were cloned and sequenced. Some of them displayed significant levels of homology with Potexviruses and Sadwaviruses. The 3’ ends of the corresponding viral genomes have been amplified by 3’ RACE, cloned and sequenced. Phylogenetic analyses confirm the existence in yams of a new viral species within the genus Potexvirus, tentatively named Yam virus X (YVX), and of a new viral species within the genus Sadwavirus, tentatively named Yam necrosis virus (YNV).