WINETECH Technical Yearbook 2021

2005). Concurrently, an Italian group, also working on genetic heterogeneity of GLRaV-3 and using the same technique, published a paper on this subject (Turturo et al ., 2005). The results of our research were published the same year, although they only appeared in printed form slightly later (Jooste & Goszczynski, 2005). The ARC-PHP laboratory deposited the full genome sequences of three divergent genetic variants of GLRaV-3, named 621, 623 and PL20 in GenBank, representing I, II and III groups of this virus (Jooste et al ., 2010). Later, we identified a highly divergent genetic variant of GLRaV-3, which represented a new and yet unknown group VII of this virus (Goszczynski 2013). The full genome sequence of a variant of this group (GH24) was determined by the Vitis Laboratory, Stellenbosch University (Maree et al ., 2015). The major contribution to worldwide knowledge on GLRaV-3 is credited to the aforementioned Stellenbosch laboratory. This includes the discovery that one of the terminal parts of the genome sequence, 5’ NTR, of this virus is 737 nt and not 158 nt as was previously published (Maree et al ., 2008). The relevance of such a long genome “tail” remains unknown. It may play an important role in the biology of this virus. Moreover, the Stellenbosch University team is a leader in establishing the clarity

of the genetic heterogeneity of GLRaV-3 (Maree et al ., 2015). The excellent work of this laboratory is reflected in many solid research and review papers, beginning in 2008 (Maree et al ., 2015, 2013 & 2008; Bester et al ., 2012; Burger et al ., 2017). Currently, six groups of divergent genetic variants of this virus are known (Thompson et al ., 2019) and this number may increase. However, despite this precise GLRaV-3 sequence data, nothing is known about the biological differences between variants of this virus. In addition to GLRaV-1, -2 and -3, there is also GLRaV-4. The presence of a virus that is serologically different from GLRaV-1, -2 and -3 was noticed relatively early, in the USA, France and Switzerland (Hu et al ., 1990; Zimmerman et al ., 1990; Gugerli & Ramel, 1993). It was named as GLRaV-4, -5 and -6. Once virus genome sequence data became available from different laboratories, and the number of putative GLRaV species amounted to eight, it emerged that some of this data represented different genetic variants of a single virus species, which was named GLRaV-4 (Aboughanem-Sabanadzovic et al ., 2017). Long before the GLRaV-4 group was created, we detected a virus named “band C closterovirus”, which cross-reacted with antibodies to GLRaV-6 (Goszczynski et

al ., 1997). The virus also cross-reacted with antisera to GLRaV-4 and -5 (Goszczynski & Kasdorf, not published). This suggested a serologically related group of viruses. Our finding was basically correct. We now know that the GLRaV-4, -5 and -6 are variants of one species, GLRaV-4. The exact identity of “band C closterovirus” remains unknown. As in the case of GLRaV-3, despite the clear genetic divergence between the presently identified eight variants of GLRaV-4, nothing is known about the differences in pathogenicity to grapevines of these variants. Among viruses associated with GRWD, there is also Grapevine rupestris stem pitting associated virus (GRSPaV). This virus has a different genome organisation from members of the genus Vitivirus , like GVA and GVB, and belongs to a separate genus, Foveavirus. GRSPaV was discovered almost concurrently in two American laboratories in 1998 (Meng & Rowhani, 2017). Soon after the full genome sequence of GRSPaV was published, research data revealed that this mysterious virus is widely present in vineyards worldwide. Because it is commonly believed that this virus is not harmful to grapevines, we paid relatively little attention to it. At some point, however, an American laboratory discovered a highly divergent variant of

this virus in grapevines affected by so- called Syrah decline (Sd) (Lima et al ., 2006). Although a high divergence between genetic variants of grapevine viruses is common, the media fuelled the suggestion that the newly-identified GRSPaV variant is associated with this disease. Sd severely affects graft of certain clones of cv. Syrah to rootstocks. Sd was identified in France and some French Syrah clones were imported to South Africa. Initially, a few mother blocks of these clones were established but, shortly after the report of Sd, propagation of these grapevines was stopped. An extensive survey conducted by the ARC- PHP revealed that none of the divergent genetic variants of GRSPaV is associated with Sd-affected grapevines in South Africa (Goszczynski, 2010). Sd is now considered a genetic disorder and not associated with any grapevine pathogen. Currently eight genetic variants of GRSPaV are known, but the pathogenicity of variants to grapevines remains a mystery (Meng & Rowhani, 2017; Goszczynski, 2020). Despite the fact that the virus is associated with grapevine rupestris stem pitting disease (GRSPD), the variants inducing symptoms of this disease in Rupestris St George grapevine have not been clearly identified (Goszczynski, 2020).

Genetic variability data is crucial for the precise detection of viruses. Currently,

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