Information Sheet
IS13004
Sugarcane mosaic
Introduction
Yield loss
Sugarcane mosaic is a disease that has been found in all
regions of the Australian sugarcane industry but is currently
restricted to the Southern region particularly the Bundaberg/
Childers district. Mosaic is widespread in the Childers district,
but management strategies have restricted the intensity
of infestations. Mosaic can cause losses of 30% or more in
susceptible varieties. Sporadic outbreaks of mosaic occur
when conditions are favourable for the aphid vectors and
susceptible varieties are grown.
Losses from sugarcane mosaic are usually not dramatic.
Infected plants can suffer yield losses of 20-30% or even
greater in ratoons. However, if the incidence of the disease
in a field is low, the overall losses are minimal. Only in highly
susceptible varieties are large patches of infected plants
usually seen.
Mosaic can disrupt disease-free (approved) seed schemes.
Careful inspection and roguing of infected plants are required
to maintain the integrity of disease-free seed plots.
Losses in Australia have been negligible because the disease is
restricted to one district and the incidence of the disease has
been kept at low levels by limiting the planting of susceptible
varieties and through disease-free seed schemes.
In Australia, we have only one strain of the sugarcane mosaic
virus. Sugarcane mosaic is caused by a range of different
viruses in other countries. In Asia and North America, mosaic
disease is very widespread and causes small losses but over
vast areas of sugarcane.
Casual agent
Sugarcane mosaic in Australia is caused by strain A of the
Sugarcane mosaic virus. Similar viruses cause disease in maize,
sorghum and Johnson grass in Australia, but these viruses
generally do not infect sugarcane in the field.
In other countries, mosaic diseases in sugarcane are caused
by sorghum mosaic virus and sugarcane streak mosaic virus.
These viruses do not occur in Australia and are serious
biosecurity threats to the Australian sugarcane industry.
Symptoms
Mosaic disease is characterised by a mottled pattern
on the leaves produced by contrasting light green to yellow
and dark green patches. The patches are irregular in shape and
have diffuse margins. Infected plants appear paler and more
yellow than healthy plants. The symptoms are most easily seen
in young rapidly growing leaves and the symptoms tend to
fade as the leaves age. In some varieties, particularly varieties
with dark red to purple stalks, the mosaic pattern can be seen
on the stalks.
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Close-up of mosaic leaf symptoms.
Information Sheet
IS13004
Diagnosis
Visual inspection for the characteristic leaf symptoms is usually
the only diagnosis required. Specific molecular diagnostic tests
are available to distinguish strains and species of the mosaic
viruses.
Spread
Mosaic can be spread by a number of aphid species in a
non-persistent manner. The aphids feed on infected plants and
spread the virus via their mouth parts for a number of days.
Aphid numbers vary from season to season. Rapid spread
of mosaic has been associated with bursts of aphid activity.
Young plants are much more susceptible than older plants, and
if aphid activity coincides with young plant or ratoon crops,
the disease spread can be dramatic.
Mosaic can also be spread by planting infected stalks. If
infected cane is planted, the resulting infected plants will act
as a source for further spread by aphids.
Mosaic is not spread by knives or harvesters, but it can be
spread by rubbing infected leaf extracts onto healthy leaves
with an abrasive pad in experimental situations.
Management
Sugarcane mosaic is managed by resistant varieties and
disease-free (approved) seed. Only a small percentage
of varieties are considered too susceptible to be grown
commercially in Australia because we have a mild strain
of the virus.
Regularly obtaining disease-free (approved) seed is important
in the management of mosaic. Disease-free seed plots must
be regularly inspected for mosaic and, if infected plants are
found, they must be immediately destroyed to prevent further
spread. Disease-free seed plots should be located away from
known sources of mosaic infection.
Controlling weeds on which the aphid vectors can breed within
fields and surrounding headlands may help to reduce spread.
Quarantine is important to prevent the spread of infected
plants to districts where mosaic is not present and to prevent
exotic strains of mosaic from entering Australia.
For further information
If you would like further information on management of
mosaic, contact your local adviser.
Reference
Grisham MP. (2000). Mosaic. In: A guide to sugarcane
diseases (eds Rott P, Comstock JC, Croft BJ and Saumtally AS.
CIRAD/ISSCT, Montpellier.
Mosaic pattern on the leaves of a susceptible variety.
sugarresearch.com.au
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