I had the great pleasure of attending the 18th International congress on viruses of the grapevine (ICVG) held on September 7-11 in Ankara, Turkey. Every three years, ICVG brings together the world’s best and brightest minds to report on the cutting-edge frontier of research on grapevine viruses and associated diseases. Last time when ICVG met in Davis in 2012, the discovery of red blotch virus was announced. No new virus has received more attention than the grapevine red blotch virus by California growers.
Highlights of red blotch research from 18th ICVG is summarized below.
Red Blotch Research Update from Dr. Marc Fuchs of Cornell University.
- Role of insect vectors is unknown;
- GRBaV infection is latent in most rootstocks;
- GRBaV is removable through microshoot-tip tissue culture;
- GRBaV appears to be spreading in some vineyards. In one vineyard, the distribution of GRBaV symptomatic vines were clustered in one end of a vineyard adjoining a riparian wetland;
- There are two distinct phylogenetic clades of GRBaV differing by about 7% in genome sequence. Effect of clade type on vine condition is unknown;
- GRBaV is widely distributed in North America in both cultivated grapes as well as in free living vines of riparian habitat;
- In one survey, GRBaV isolates from free-living vines fall within clade 2, as do the majority of isolates from adjoining vineyard blocks. This suggests that free-living grapes have the potential to serve as reservoirs of GRBaV.
Red Blotch Research Update from Dr. Naidu Rayapati of Washington State University.
- Surveyed 546 symptomatic samples representing 11 red-berry cultivars and 30 samples representing 4 white-berry cultivars for GLRaV-3 and GRBaV from six AVA areas in Washington state;
- 82% samples tested positive for GLRaV-3 or GRBaV (i.e. single infection);
- 18% samples tested positive for both GLRaV-3 and GRBaV (i.e. co-infection)
- Among the 82% samples with single infections, 71% and 29% samples were positive for GLRaV-3 and GRBaV respectively.
Red Blotch Research Update from Dr. Jean-Sebastien Reynard of Switzerland.
- Two accessions, Zinfandel A2V13 and Emperor A2V18 imported from UCDavis in 1985, were found to be infected with GRBaV;
- GRBaV infection reduced vine’s photosynthetic capability by a range of 27% to 44% as measured by three parameters;
- GRBaV infection reduced leaf chlorophyll content by about 13% at time of verasion;
- GRBaV infection reduces soluble solids content and tartaric acid by 10% and 14% respectively, but increased malic acid by 22%;
- Virus monitoring should be undertaken in order to verify if GRBaV is restricted to only to North America
- GRBaV should be included in certification program
In addition to red blotch, advances in new technology such as next generation sequencing have enabled the discovery of other new viruses. Some examples are as follows.
- A DNA virus named “Roditis leaf discoloration-associated virus (GRLDaV)” was discovered in 2015 by researchers in Greece. This is the third DNA virus in grapevines after grapevine vein clearing virus and grapevine red blotch virus;
- A new virus named grapevine cabernet sauvignon reovirus. (GCSV) was reported in 2015 by UCDavis. The etiological relationship of this virus with a disease is unclear;
- Although grapevine pinot gris virus (GPGV) was reported in 2012 by Italian researchers, it is not until recently that the association of this virus with a disease starts to emerge. It s related to an emergent pathology characterized by stunting, leaf deformation, chlorotic mottling and mosaic. GPGV is now found in most wine growing regions of Europe. To the best of our knowledge, no GPGV has been reported in North America.
Toward the Future
Looking into the future, Professor Martelli of Italy presented the following insight – a view shared by his colleagues in their joint publication. “The challenge and target of future research is not so much the development of more refined and highly performing techniques for the recognition and elimination of viruses but, rather, the design of dependable strategies for preventing a quick sanitary deterioration of vineyards planted with costly certified materials.” (Maliogka V, Martelli GP, Fuchs M, Katis NI, 2015, Advances in Virus Research 91, 175-227.)
To this end, we continue to encourage growers to be vigilant to survey existing vineyards so as to remove an infected vines and to test new planting materials so as to prevent any infected vines from being planted in new vineyards.
For more information, please contact:
Dr. Alan Wei
930 Riverside Parkway, Suite #30
West Sacramento, CA 95605