Résumé
The objective of this study is to retrieve virus sequences from preserved plant specimens currently held within French and South African herbaria and use these to provide both a temporal element to our viral diversity studies, and a means of increasing the accuracy with which key infectious ancestral virus genotypes can be reconstructed. Besides providing nucleotide sequences from old virus species, it will provide temporal structure to many of the contemporary virus sequence datasets that we obtain from our contemporary field sampling surveys. Given the sampling locations and times of the ancient and contemporary viruses we should be able to accurately estimate when and where key ancestral plant viruses existed. However, because ancient DNA/RNA are degraded and rare, a first step towards reaching this ambitious objective is to set methodological studies focusing on viral nucleic acid extraction and amplification. We here present preliminary results of these methodological studies focusing (i) on the most appropriate RNA extraction method using herbarium plant specimens and (ii) on the minimal weight of herbarium plant specimen samples that can be used for reliably recovering ancient RNA. These studies were based on a herbarium oat specimen naturally infected by the barley yellow dwarf virus. (Résumé d'auteur)