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.

Null alleles are alleles that are recessive to codominant markers without any effect on the phenotype. In SSR assays, there are several reasons for the lack of amplification at a locus: the primer does not bind well, longer fragments do not amplify due to imperfections in the PCR reaction, or the amount of DNA in the sample is insufficient. In microsatellite studies, null alleles are mostly used in pedigree analysis and population genetics calculations such as diversity estimation. Null alleles in pedigree analysis can cause rejection of the true parent; if not recognized while in population genetics they distort the results in underestimating diversity. In this review, the effects caused by null-alleles in viticultural research and its possible solutions were summarized.

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.

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.

As the sensitivity of perennial crops to climate change becomes more pronounced, clonal selection, which is already very time-consuming for grapevine, may take even longer, while its importance is increasing. In the case of indigenous grapevine varieties, the purpose of clonal selection is twofold: to mitigate problems of cultivation and at the same time, to preserve the varietal character. The cultivation technique issue of ‘Kéknyelű’ is the low fertility (functionally female-flowered variety), and as for ‘Juhfark’ it is the significant susceptibility to grey rot. Based on daily meteorological data of 11 years, the years were classified into 3 groups and harvest data were analyzed within each group. Significant difference in yield was found between clone B.2. and the base ‘Kéknyelű’. Both clones of ‘Kéknyelű’ matured with significantly lower pH compared to the base variety. Given the acidic character of ‘Kéknyelű’ wine and the predicted rise in must °Brix and pH as a result of climate change, these differences may be useful in the future. Botrytis infection only showed statistically significant differences between year groups for ‘Juhfark’. It is intriguing that in most years, the rate of grey rot infection was lower in both clones compared to the base variety, especially in year groups 1 and 3 when the overall rate of Botrytis infection was quite low.

Maintaining grape cultivation requires the continuous production of healthy propagating material and the control of economically important viruses. For more effective virus eradication, it is beneficial to try chemotherapeutic agents that have not yet been used on grapevine. We therefore tested two chemotherapeutic agents with different mechanisms of action (2-thiouracil and zidovudine) in addition to ribavirin, which is already used on grapevine. Viruses and viroids were identified in the mother plants of different grapevine cultivars by small RNA HTS (High-Throughput Sequencing), and RT-PCR verified the results. After chemotherapy, the regenerated plants were tested using RT-PCR and the efficacy of the three chemotherapeutic compounds was evaluated. Among the tested agents, ribavirin had the broadest elimination effect (the virus was not detectable by RT-PCR after 8 months) on most viruses. It proved to be particularly effective (the virus was not detectable by RT-PCR in most of the tested plants) against GFkV, GLRaV-4, GPGV and GRSPaV. The use of 2-thiouracil caused high phytotoxicity and was effective against GLRaV-4 among the viruses tested, having no effect on the other viruses. Zidovudine alone failed to eliminate any of the viruses we tested. 2-thiouracil, ribavirin and zidovudine were unable to eliminate HSVd and GYSVd-1 viroids.