Résumé
French West Indies Biological Resources Centre for Tropical Plants (CRB-PT) maintains several germplasm collections of tropical crops and wild relatives, including a collection of 480 yam accessions (Dioscorea spp.) in vitroculture. The purpose of this Centre is to conserve this biodiversity and distribute virus-free germplasm to end users. To this aim, virus populations infecting conserved accessions have been characterized and the diversity of intra and inter-species highlighted through the SafePGR project. Thus, three new virus generi have been found out (Ampelovirus, Macluravirus and a Secoviridae member) besides those existing (Badnavirus [1], Potyvirus [2] and Potexvirus [3]). Efficient extraction method and appropriate detection tools have been created and/or optimized, then implemented for an initial diagnosis of the in vitro collection. Prevalence shown that more than 75% of yam accessions are infected by Potyvirus, 80% of D. alata, the most cultivated yam, are infected by the new yam virus Ampelovirus and Macluravirus are only present in this yam species. Only 19 accessions remained free of viruses, but the majority of the collection contained one, two or more of viruses, so the necessity to sanitize the infected germplasm. The sanitation process consists to submit shoots to thermotherapy at 34°C, then excise apical meristem and obtain the regeneration of a new plant, expecting to be free of viruses. Using optimized detection tools, each new plant is diagnosed for the six viral generi. Up to now, the sanitation process leads to the achievement of 10 accessions completely virus-free. The development and yield of this improved plant material have to be evaluated by comparison of infected and sanitized accessions. Macluravirus, which only infects D. alata with a low prevalence, are removed quite easily (100% of sanitation). YMV, which leads the strongest loss of yield in yam, has a good sanitation rate of 56% and YMMV, that infects 76% of the collection, has a sanitation rate of only 16%. The sanitation is a time-consuming process, not quite efficient, but necessary for yam germplasm international exchange. (Résumé d'auteur)