Meristem culture and somatic embryogenesis are effective tools for virus elimination of vegetatively propagated crops including grapevine (Vitis vinifera L.). While both have been shown to be useful to eliminate the main grapevine viruses, their efficiency differs depending on the virus and grapevine variety. In our work, we investigated the efficiency of these two virus elimination methods using small RNA high-throughput sequencing (HTS) and RT-PCR as virus diagnostics. Field grown mother plants of four clones representing three cultivars, infected with different viruses and viroids, were selected for elimination via somatic embryogenesis (SE) and meristem culture (ME). Our results show for the first time that using SE, elimination in mother plants was effective for all viruses, i.e., grapevine rupestris vein feathering virus (GRVFV), grapevine Syrah virus 1 (GSyV-1), Grapevine virus T (GVT) and grapevine Pinot gris virus (GPGV). This study also confirms previous studies showing that SE is a possible strategy for the elimination of GFkV, GRSPaV, HSVd, and GYSVd-1. Our results demonstrate that the efficacy of virus elimination via SE is relatively high while the purging of viroids is lower. Our work provides evidence that the efficiency of SE is comparable to that of the technically difficult ME technique, and that SE will offer a more effective strategy for the production of virus-free grapevine in the future.

Grapevine virus T (GVT) is a recently described foveavirus, which was identified from a transcriptome of a Teroldego grapevine cultivar in 2017. Recently, we surveyed vineyards and rootstock plantations in Hungary using small RNA (sRNA) high-throughput sequencing (HTS), at a time when GVT had not yet been described. A re-analysis of our sRNA HTS datasets and a survey of grapevines by RT-PCR revealed the presence of GVT in most of the vineyards tested, while at rootstock fields its presence was very rare. The presence and high variability of the virus in the country was confirmed by sequence analysis of strains originating from different vineyards. In this study, we demonstrate the presence of GVT in Hungary and show its high diversity, suggesting that GVT presence may not seriously affect grapevine health and that it could have been present in European vineyards for a long time as a latent infection.

Somatic embryogenesis (SE) is a widely used technique in plant biotechnology, and it can be a possible tool for virus and viroid elimination. This review highlights the advantages and limitations of production of pathogen-free plants using somatic embryogenesis. Beside the well-known meristem cultures, chemotherapy, thermotherapy and cryotherapy, SE is a very effective virus and viroid elimination method. Production of virus- and viroid-free plants is categorized based on the latest virus taxonomy. The available information on virus and viroid spread in calli and the effect of SE on morphological and genetic stability of the regenerated plants are presented in details. A number of factors which could affect the efficiency of this technique are also pointed out. Based on the collected and analysed data, SE can be a useful option for virus and viroid elimination.

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