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The prevalence of badnaviruses in West African yams (Dioscorea cayenensis-rotundata) and evidence of endogenous pararetrovirus sequences in their genomes

Seal S., Turaki A., Muller E., Lava Kumar P., Kenyon L., Filloux D., Galzi S., Lopez-Montes A., Iskra Caruana M.L.. 2014. Virus Research, 186 : p. 144-145. International Plant Virus Epidemiology Symposium. 12, 2013-01-28/2013-02-01, Arusha (Tanzanie).

Yam (Dioscorea spp.) is an important vegetatively-propagated staple crop in West Africa. Viruses are pervasive in yam worldwide, decreasing growth and yield, as well as hindering the international movement of germplasm. Badnaviruses have been reported to be the most prevalent in yam, and genomes of some other badnaviruses are known to be integrated in their host plant species. However, it was not clear if a similar scenario occurs in Dioscorea yam. This study was conducted to verify the prevalence of badnaviruses, and determine if badnavirus genomes are integrated in the yam genome. Leaf samples (n = 58) representing eight species of yam from global yam collections kept at CIRAD, France, and 127 samples of D. rotundata breeding lines (n = 112) and landraces (n = 15) at IITA, Nigeria, were screened using generic badnavirus PCR primers. Positive amplification of an expected ca. 579 bp fragment, corresponding to a partial RT-RNaseH region, was detected in 47 (81%) of 58 samples analysed from CIRAD collections, and 100% of the 127 IITA D. rotundata samples. All the D. cayenensis and D. rotundata samples from the CIRAD and IITA collections tested PCR-positive, and sequencing of a selection of the PCR products confirmed they were typical of the genus Badnavirus. A comparison of serological and nucleic acid techniques was used to investigate whether the PCR-positives were sequences amplified from badnavirus particles or putative endogenous badnavirus sequences in the yam genome. Protein A sandwich-enzyme-linked immunosorbent assay (PAS-ELISA) with badnavirus polyclonal antisera detected cross-reacting viral particles in only 60% (92 of 153) of the CIRAD collection samples analysed, in contrast to the aforementioned 81% by PCR. Immunosorbent electron microscopy (ISEM) of virus preparations of a select set of 16 samples, representing different combinations of positive and negative PCR and PAS-ELISA results, identified bacilliform particles in 11 of these samples. Three PCR-p

Mots-clés : dioscorea; dioscorea rotundata; dioscorea cayenensis; virus des végétaux; morbidité; identification; génome; test elisa; pcr; microscopie; séquence nucléotidique; france; nigéria; dioscorea cayenensis rotundata; badnavirus; pararétrovirus; endovirus

Thématique : Maladies des plantes; Méthodes de relevé

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