Page 55 - Grapevine July-August 2019

Around The Vineyard

wine regions. Although all leafroll associated virus-
es belong to the Closteroviridae (Greek, clostero:
thread-like) family, the only species known to be
transmitted by insects are found in the Ampelovirus
genus (Greek, ampelos: grapevine). Ampeloviruses
include the majority of Grapevine leafroll associ-
ated viruses (GLRaV-1, -3, and -4). So far, no vec-
tor has been reported for GLRaV -2 or GLRaV-7
(but as other viruses are propagated by cuttings).
Research has shown that leafroll viruses are able
to recombine in mixed infections, generating many
variants of similar viruses that scientists define
as a quasispecies (i.e., almost a species). These
genomic changes have serious implications on virus
detection as standard methods may miss infection.
Transmission by mealybug and soft scale insects
has been reported for GLRaV-1, -3, and -4. Different
mealibugs such as the grape (Pseudococcus
maritimus), citrus (Planococcus citri), long-tailed
(Pseudococcus longispinus), obscure (Pseudococcus
viburni) and vine (Planococcus ficus) are able to
transmit Ampeloviruses and Vitiviruses non-specifi-
cally. Furthermore, work in South Africa has shown
that a single individual of vine or long-tailed mealy-
bug is capable of starting a GLRaV-3 infection.

Sampling in The Vineyard:

The correct identification of the disease caus-
al agent is critical for devising a control strategy.
Regular visual inspections and sampling of grape-
vines should be performed to monitor the disease
status of a vineyard. It might not always be possible
to correlate the presence of virus infection with
symptoms, especially with new viral infections.
Complicating matters, other viruses, fungi, or
nutritional deficiencies can cause similar symp-
toms in grapevines. Furthermore, vines planted on
their own roots do not develop typical symptoms.
Symptoms may appear two or more years after
top-working a vineyard with a new variety. Viruses
associated with leafroll move slowly in the vine
and may remain undetected by laboratory testing,
unless sampling is done correctly. Collection of
representative samples will allow the laboratory
to detect the presence of viruses associated with
leafroll. The season for testing is important and
samples should be collected from vines late in the
summer throughout dormancy.

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