Virus Season

Since virus season is rapidly approaching with impending winter, I thought it would be a good time to talk about viruses.  Particularly, grapevine viruses.  In this entry, I will talk about one in particular…

There are actually a number of grapevine diseases, let alone viruses, out there. According to UC Davis,

grapevines can harbor more than 55 virus and virus-like diseases that cause a range of symptoms from severely damaging (some killing grapevines), to others considered mild with little or not economic impact.

Though, other sources indicate numbers up to 75.  The vectors and spread of most of these diseases are known.  However, there are some viruses for which this information is still unknown.  Of particular note is Grapevine Red Blotch associated Virus (GRBaV), or Red Blotch for short.

Red Blotch was first found in Napa Valley in 2008.  Now, it is found widely throughout North America in both cultivated and wild vines.  The most notable symptom of infection is the reddening of the leaves, hence the name.  In fact, the beautiful red coloring you see in vineyards at fall is actually due to viral infection (with Red Blotch and others).  Leaves are supposed to go from green to yellow to brown.  Never red.

Red Blotch Virus
Red Blotch Virus

Nonetheless, the virus reduces photosynthetic capacity (by reducing leaf chlorophyll content), thus reducing both sugar levels and quantity.  It can also reduce tartaric acid (main acid in grapes) and quality of the fruit.  These factors can then lead to poor wine, as the quality of the grapes is the leading factor in wine quality.

So, we know what it does to grapes, but how does it spread? Well, it can be transmitted via grafting (connecting an infected rootstock or scion to another rootstock or scion).  Easy solution that comes to mind: just don’t use contaminated material when grafting, right? Well, not quite.  The virus can still spread through vineyards, even if you obtain clean plant material for grafting, verified by PCR and genetic analysis.

Generally, spread of Red Blotch is typically located near wetlands, streams, and other water sources.  The presence of the virus is also associated with wild vines, or “free-living” vines, in the area.  It has been suggested these wild vines could be a reservoir for the virus.  If a contaminated vineyard were ever replanted, the wild vines could then serve as patient 0 and infect the brand-new pristine vines.  Unfortunately, this still does not answer the question of the virus spreads from vine to vine in any given vineyard?  Many scientists are currently trying to elucidate an insect vector, but one is currently unknown.  Until then, careful maintenance, monitoring, and consideration when planting needs to be taken in order to limit the spread of Red Blotch!

Red Bloth

To be continued…

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