Red Blotch Disease of Grapes – An Incomplete Story

This past summer, two research groups, one in Cornell and the other in UC Davis, reported discovering a novel DNA-­‐virus from grapes. The virus was named as Cabernet Franc-­associated virus (GCFaV) by the group in Cornell, and as Grapevine red blotch associated virus (GRBaV) by the scientists in UC Davis. The later name was given because of the symptoms: blotchy, red leaves with red veins, that were found to be associated with the presence of this virus.

Because of some misleading alarmist information has been released to growers, we at AL&L Crop Solutions found it necessary to clarify the status and the significance of this virus.

First, before GRBaV can be named as a causal agent of the red blotch disease, a lot more research and information needs to be obtained. Just the fact that the organism has been found to be associated with the disease, does not make it a pathogen, capable of causing the disease.

In plant pathology research, when a finding of an organism in a host plant, such as grapes, is made, very careful studies need to be completed where the organism, as a pure culture, is back‐inoculated to a healthy vine that does not harbor that organism. Then, the same symptoms that were observed in the original vine have to be reproduced in the newly inoculated vine. Moreover, from that inoculated, symptomatic vine, the same organism it was inoculated with needs to be recovered. These steps, also called as Koch’s postulates, have to be fulfilled before the organism gets a title as being a causal agent of the disease. For Red blotch disease, these steps have not yet been fulfilled.

Second, the GRBaV is apparently a novel‐type of DNA virus, and only distantly related to geminiviruses, a group of DNA viruses causing significant diseases in other crops. While it shares some structural similarities with viruses in that family, its genome is significantly different with only 50% similarity at sequence level. This means that it is too early and too speculative to make assumptions about the significance of this virus in grapes. With any questions or concerns, please do not hesitate to contact our plant disease diagnostic professional:

Anna‐Liisa Fabritius, Ph.D
Plant Pathologist
Email: annaliisa@allcropsolutions.com

Additional Resources:

 

• For a downloadable PDF copy of this article, please click here.

• UC Davis Red Blotch Disease Information PDF: Download here