Symptomatology and effects of viruses associated with rugose wood complex on the growth of four different rootstocks

The rootstocks Vitis rupestris cv. St. George, Kober 5BB, LN33, and Freedom were graft-inoculated with viruses associated with the rugose wood complex (RW) to study their growth response and symptom expression. The virus sources used in this study were isolates LR127, CB111, CB105, and PA94-142 for Grapevine virus A (GVA), CB120 for Grapevine virus B (GVB), LV92-07 and a field selection of Chardonnay for Grapevine virus D (GVD), and a field selection of Cabernet Sauvignon for Grapevine rupestris stem pitting-associated virus (GRSPaV). Each rootstock plant was graft-inoculated with one, two, or three virus sources using bud chips from virus-infected grapevines. Plants were planted following a partially randomized block design. After two years, plant diameter was measured, barks were removed, and the woody cylinders were observed for the presence of RW symptoms and rated based on symptom severity. Selected plants were also tested by RT-PCR. The study showed that the greatest reduction in trunk diameter was in plants inoculated with the virus source combination of GVB/GVD/GRSPaV regardless of the rootstock type. Furthermore, treatments GVB/GVD, GVA/GVB/GVD and GVB/GVD/GRSPaV had the highest effect on LN33 growth, and GVA/GVB/GRSPaV, GVB/GVD/GRSPaV, and GVA/GVB had the highest growth effects on Kober 5BB. In general, GVB source had more adverse effect on growth in multiple infections, particularly in triple combination. In treatments with single virus source, GVD showed severe growth reduction in Freedom with no symptoms on the woody cylinder of the plants. Some sources of GVA impaired the growth of both Kober 5BB and Freedom rootstocks.