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International audience; The genus Dioscorea hosts a large number of yam species used medicinally and as a staple food by millions of people in tropical countries. All yams share a high antioxidant activity that correlates with their total phenolics contents. However, knowledge of edible species antioxidant phenolics remains incomplete. Bioassay-guided fractionation of the tubers of a yam species with high total phenolics content, D. nummularia, led to the isolation of two flavonols, caryatin and 3 ′-O-methyl caryatin, contributing over 92% of a stable methanol extract of the tuber in this species. Their structures were determined by high resolution mass spectrometry (HRMS), nuclear magnetic resonance (NMR) and a synthesized authentic sample. They displayed no bacterial toxicity. Their content was estimated in the tubers and bulbils of 411 landraces and hybrids belonging to eight food yam species using high performance-thin layer chromatography (HP-TLC). These were found to be highly variable at the intra-and interspecific levels to reach up to 1 030 and 457 μg/g DW respectively and added up to contents of already described antioxidant phenolics. This study provides additional understanding of the health benefits of a yam diet and constitutes the first phytochemical analysis of D. nummularia.

Analysis of deposits at a Lapita site in Vanuatu revealed putative starch grains of Dioscorea nummularia in ~2800–3100cal. BP layers and of Dioscorea pentaphylla in a ~2000 cal. BP layer, suggesting local cultivation of these tuberous crops. The Dioscoreaceae are a new addition to the introduced cultigens thus far directly identified for prehistoric Vanuatu.

UMR DAP; International audience; Amplified fragment length polymorphism markers were used to assess the genetic relatedness between Dioscorea alata and nine other edible Dioscorea. These species include D. abyssinica Hoch., D. bulbifera L., D. cayenensis-rotundata Lamk. et Poir., D. esculenta Burk., D. nummularia Lam., D. pentaphylla L., D. persimilis Prain. et Burk., D. transversa Br. and D. trifida L. Four successive studies were conducted with emphasis on the genetic relationship within D. alata and among species of the Enantiophyllum section from Vanuatu. Study 1 was carried out to select a set of polymorphic primer pairs using 11 combinations and eight species belonging to five distinct sections. The four most polymorphic primer pairs were used in study 2 among six species of the Enantiophyllum section. Study 3 focussed mainly on the genetic relationship among 83 accessions of D. alata, mostly from Vanuatu (78 acc.) but also from Benin, Guadeloupe, New Caledonia and Vietnam. The ploidy level of 53 accessions was determined and results indicated the presence of tetraploid, hexaploid and octoploid cultivars. Study 4, included 35 accessions of D. alata, D. nummularia and D. transversa and was conducted using two primer pairs to verify the taxonomical identity of thecultivars ‘langlang’, ‘maro’ and ‘netsar’ from Vanuatu. The overall results indicated that each accession can be fingerprinted uniquely with AFLP. D. alata is an heterogeneous species which shares a common genetic background with D. nummularia and ‘langlang’, ‘maro’ and ‘netsar’. UPGMA cluster analysis revealed the existence of three major groups of genotypes within D. alata, each assembling accessions from distant geographical origins and different ploidy levels. The analysis also revealed that ‘langlang’, ‘maro’ and ‘netsar’ clustered together with the cultivar ‘wael’ (D. transversa) from New Caledonia. Results are discussed in the paper

International audience; The genome of yam virus X (YVX), a new member of the genus Potexvirus from yam (Dioscorea trifida), was completely sequenced. Structural and phylogenetic analysis showed that the closest relative of YVX is nerine virus X. A prevalence study found YVX only in plants maintained in Guadeloupe and showed that it also infects members of the complex D. cayenensis rotundata. This study provides evidence for the existence of two additional potexviruses, one of which infects D. nummularia in Vanuatu and the other, D. bulbifera and D. rotundata in Haiti and D. trifida and D. rotundata in Guadeloupe. This work also shows that existing potexvirus-specific degenerate primers targeting the ORF1-encoded polymerase domain are well suited for the identification of the three potexviruses reported here.