Page 41 - Grapevine NovDec 2020

Around The Vineyard
Around The Vineyard

tissue cultured grapevine plants. Time will tell,
after the plants grow, if the infected vines also dis-
play the detrimental effect of the virus in organo-
leptic qualities of the fruit (i.e., reduction of sugar).

Viral Symptoms are Remarkably Similar

Vines infected with leafroll viruses produce small-
er grape clusters that ripen unevenly with lower
sugar content. Foliar symptoms include downward
rolling, reddening or yellowing of leaves depending
on the grapevine variety. Other foliar colors associ-
ated with leafroll virus infection include pink, pur-
ple, and orange speckles. The leaf veins may remain
green or take many other colors (yellow, purple, or
red). Grapevine red blotch virus infection may dis-
play different red leaf discoloration which usually
appear spotty or blotchy.

However, these symptoms are indistinguishable
from leafroll, especially when rolling of leaves are
absent in GLRaV- infected vines. In some cases,
GRBV infected vines may display red veins, but
red veins have also been observed in non-infected
vines, and many red-blotch infected vines do not
display red veins.

In my opinion, red vein symptoms cannot be used
as a diagnostic tool. In white-fruited varieties red
blotch disease displays yellow blotchy discoloration
in leaves. While the symptoms of leafroll and red
blotch can be confused, these diseases are caused
by different types of viruses that can often be
found in mixed infections, complicating the visual
diagnosis. Although, the change in colors of the
leaves in the fall is a tale-tell of virus infection, the
most important negative effect of both GLRaV and
GRBV infection is the reduction of sugar in fruit
resulting in reduced Brix values and delayed fruit
maturity.

Some GLRaVs and their strains are more aggres-
sive than others. Researchers have described the
Alfie (Australia and New Zealand), BD (Italy), and
Red Globe (U.S.A) strains of GLRaV-2. These strains
are molecularly similar and have been associated
with graft incompatibility, vine decline and death.
Some researchers report that GLRaV-1 and -3
induce more severe symptoms than GLRaV-4.

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