Agriculture Reference
In-Depth Information
Fig. 7.7
Botrytis cinerea
(or
grey mold) on a Chardon-
nay bunch. Note the various
stages of infection along the
bunch
Infection of grape berries by Botrytis frequently occurs when berries split in the
bunch. Berry splitting can occur following heavy rain periods when there is a sud-
den uptake of water and also following other weather events, such as hail damage.
Bird damage can also be a problem, in fact anything that breaks the skin of the berry
can lead to bunch rot development. The skin of the berry is thus a natural barrier
to infection, and once this is broken then berries are susceptible to disease. Berry
splitting is common in grape varieties that have a tight bunch structure, Pinot noir is
such an example, while bunches with a looser structure, e.g. Shiraz tends to get less
Botrytis simply because berry splitting is less likely to occur. Another way in which
this disease is spread is via the activities of an insect, larvae of the Light Brown
Apple Moth (LBAM) which feed on the interior of the bunches. Aside from damag-
ing tissue which allows for infection, it has been shown that the LBAM larvae can
also carry fungal spores on their bodies, leading to disease spread.
Grey mould frequently occurs in regions of the globe where summers are cool
and wet, moisture is important for growth of the fungus and the fungus tends to
grow best around 25 °C.
Impact on Wine
Aside from a loss of yield, the fungus produces an enzyme, called laccase and this
can be a problem in red wine production, since laccase is an oxidative enzyme that
can reduce the colour content of red wine. The fungus also converts the berry sugar
(glucose and fructose) in to glycerol and produces a range of polysaccharides called
glucans. Glucans are large molecular weight compounds that can cause problems
when wine is filtered, causing blockages in the filtration process. As with most
moulds the disease often imparts musty, mouldy characters on the wine (Steel et al.
2013
).
