Grape Vine Red Blotch Associated Virus

Ebola is on our minds, but we easily forget that the biosphere is a churning cauldron of microbes whose tenure on the planet extends back several billion years. They live deep in the earth’s crust. They live in the mesosphere. They live in bedrock lakes beneath the ice in Antarctica. And that’s just where we’ve bothered to look. Any shovel full of dirt from your backyard would reveal creatures unknown to science if you had the patience to do a comprehensive survey.

Viruses and prions are scraps of nucleic acids that have found niches as wayfarers wandering through the genomes of more complex creatures. Most are submicroscopic and so poorly understood that you might well spend a good part of your life trying to catalogue these creatures in that same shovel full of dirt from your backyard.

We ignore them until they kick us in the butt.

When people began noticing red leaves on  grape vines that seemed to ripen slower late in the last decade  they tested for the leafroll virus that produces similar symptoms. Some actually had leafroll but others did not and further genetic investigation revealed a “new” circular, single stranded DNA virus distantly related to the Gemini viruses.


We tend to jump way too quickly from correlation to causation and many plants infected with the “new” virus are also infected with leafroll, but not all. Separate groups in several areas of the United States and Canada isolated the virus soon thereafter and gave it different names, but the consensus is that it is all the same virus and judging from its wide distribution it has probably been around for a long time, unnoticed.

Kind of like attention deficit disorder, completely undiagnosed when I was daydreaming through dull classes as a kid, but now the explanation for everything from laziness to psychopathic behavior.

But it is a serious problem if it is actually causing the reddening leaves slow ripening, which seems likely. One group has suggested the possibility that a fungus is associated with the disease and it seems very possible that a complicated set of interactions may affect the expression and virulence.

Underside redening veins

What seems to distinguish red blotch symptoms from Potassium and Phosphorus deficiencies, mite damage, and leafroll virus–all of which produce red leaves–is the reddening of the veins in the leaf. Sometimes this reddening of the veins is not apparent from the top and the leaf must be turned over like this one.

The biology of viruses and the knowledge of the sequencing techniques necessary to identify them is very difficult stuff that requires years of study to master, but the epidemiology of this disease–how it behaves and spreads in the vineyard–is virtually unknown. One can read the entire published knowledge base in an afternoon.

In cases like this, citizen scientists, those willing to carefully watch and learn, can be a valuable addition to the study of the disease.

We are accustomed to the leaves in our forests turning red in the harvest season and to the casual observer the sight of a red vineyard in the autumn can be a peaceful and beautiful spectacle. Grape vines should turn yellow, not red, and to those who work with the vines it is anything but a peaceful and beautiful spectacle. It means there is a lot of work to do because something is definitely wrong, and it may be a certain newly discovered circular virus with 3206 base pairs.


This entry was posted in Biology, Microbial Dark Matter, Wine and tagged , , . Bookmark the permalink.

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