Abstract
Despite the increasing impact of Grapevine Pinot gris disease (GPG-disease) worldwide, etiology about this disorder is still uncertain. The presence of the putative causal agent, the Grapevine Pinot Gris Virus (GPGV), has been reported in symptomatic grapevines (presenting stunting, chlorotic mottling, and leaf deformation) as well as in symptom-free plants. Moreover, information on virus localization in grapevine tissues and virus-plant interactions at the cytological level is missing at all. Ultrastructural and cytochemical investigations were undertaken to detect virus particles and the associated cytopathic effects in field-grown grapevine showing different symptom severity. Asymptomatic greenhouse-grown grapevines, which tested negative for GPGV by real time RT-PCR, were sampled as controls. Multiplex real-time RT-PCR and ELISA tests excluded the presence of viruses included in the Italian certification program both in field-grown and greenhouse-grown grapevines. Conversely, evidence was found for ubiquitous presence of Grapevine Rupestris Stem Pitting-associated Virus (GRSPaV), Hop Stunt Viroid (HSVd), and Grapevine Yellow Speckle Viroid 1 (GYSVd-1) in both plant groups. Moreover, in every field-grown grapevine, GPGV was detected by real-time RT-PCR. Ultrastructural observations and immunogold labelling assays showed filamentous flexuous viruses in the bundle sheath cells, often located inside membrane-bound organelles. No cytological differences were observed among field-grown grapevine samples showing different symptom severity. GPGV localization and associated ultrastructural modifications are reported and discussed, in the perspective of assisting management and control of the disease.
Highlights
Grapevine Pinot gris disease (GPG-disease) first occurred in 2003 in Northern Italy, when symptoms reminiscent of viral diseases were initially detected on cv
Dormant canes and leaves were tested by real-time RT-PCR and ELISA for the viruses included in the Italian certification program (Bertazzon et al 2002), namely Grapevine Viruses A and B (GVA, GVB), Grapevine Fleck Virus (GFkV), Grapevine Leafroll-associated Viruses 1, 2, 3 (GLRaV-1, GLRaV-2, GLRaV-3), Grapevine Fanleaf Virus (GFLV), and Arabis Mosaic Virus (ArMV)
The absence of the viruses included in the Italian certification program (GVA, GVB, GFLV, ArMV, GFkV, GLRaV-1, GLRaV-2, and GLRaV-3, Bertazzon et al 2002), and the ubiquitous presence of Grapevine Rupestris Stem Pitting-associated Virus (GRSPaV) and grapevine viroids Hop Stunt Viroid (HSVd) and Grapevine Yellow Speckle Viroid 1 (GYSVd-1) (Martelli et al 2007; Meng et al 2006), both in the field- and greenhouse-grown control grapevines, allowed us to focus on Grapevine Pinot Gris Virus (GPGV)-plant interactions
Summary
Grapevine Pinot gris disease (GPG-disease) first occurred in 2003 in Northern Italy, when symptoms reminiscent of viral diseases were initially detected on cv. Next-generation sequencing approaches and small-RNA analyses have been applied to symptomatic grapevine tissues and led to the identification of a new virus, provisionally named Grapevine Pinot Gris Virus (GPGV; Giampetruzzi et al 2012). GPGV has a positive-sense single-stranded RNA genome. It has been included in the order Tymovirales and in the recently established Betaflexiviridae virus family, genus. GPGVoccurs in different grapevine cultivars, such as Pinot gris, Pinot noir, Traminer, Tocai, and Glera, and it can be present both in symptomatic and asymptomatic plants (Bianchi et al 2015; Saldarelli et al 2015). The wide difference in symptom severity and the molecular detection of the virus in asymptomatic plants indicate the lack of an unambiguous correlation between the occurrence of the syndrome and the newly described virus
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