THE BSES REPORT
Just when you thought
you could relax
S
ince 2006, growers have necessarily focused on managing sugarcane
smut disease. It appears now that
they must also be on the lookout for the
re-emergence of another very unwelcome
sugarcane disease; a disease that thrives
during wet years like this current season
and can significantly affect dollar returns
– chlorotic streak.
“Chlorotic streak remains one of the
most widespread and common diseases in
the Australian sugarcane industry,” says
BSES plant pathologist Dr Rob Magarey.
“The increase in this disease likely comes
from two years of solid wet seasons which
in turn has carried what little infection we
did have far and wide.”
“In some areas, the disease has spread
from planting cane which was already infected by chlorotic streak – plant source
inspections from productivity board staff
members are vital.”
In order to combat sugarcane smut,
growers have been changing to more
smut-resistant varieties. Unfortunately
some of these are subject to attack from
chlorotic streak. The disease has been
Know your enemy
– chlorotic streak
Chlorotic streak is found in all
sugarcane growing areas in eastern
Australia and can cause serious yield
losses, particularly in flood prone or
waterlogged parts of the industry. The
disease is one of the most widespread
and common diseases within the
Australian sugar industry.
seen in Q183**, Q200**, Q226**, and
Q238** over the past season in the central region, so care should be taken when
selecting planting material of these varieties. Q208** appears to be more resistant
to the disease.
Causal organism
Despite a significant research effort undertaken over an 80 year period in many
countries around the world, the causal
agent of chlorotic streak has not been
identified.
This has hindered diagnosis and other
aspects of managing the disease. The dis-
ease has some characteristics indicative of
a virus but no one has been able to confirm the true cause of the disease.
Symptoms
The main symptoms of chlorotic streak
are irregular creamy-white streaks with
indistinct margins. The streaks often fade
and reappear as they extend along the
leaf. As the disease progresses, many
streaks develop dead sections of leaf tissue
along the streaks. There may be one or
more streaks per leaf.
If stalks with chlorotic streak are sliced
lengthwise, short red streaks will be seen
running through the nodes; these streaks
are longer than those seen with ratoon
stunting disease.
Diagnosis
There is currently no assay for the disease – therefore diagnosis is based on
visual symptoms.
Yield loss
Cane infected with chlorotic streak will
lack vigour leading to yield reductions of
up to 40 per cent. Poor ratooning is also a
characteristic of this disease.
Spread
Chlorotic streak is spread by diseased
planting material, and by soil water. The
disease is most common in areas prone to
flooding and/or water logging. The combination of the disease and the deleterious
effects of water logging can compound the
yield losses suffered in infested fields.
The disease can survive for several
months in the absence of the sugarcane
plant once a field is infested.
Recycled irrigation water that has
passed through infested fields can spread
the disease to the next field that is irrigated
with the water.
The disease is not transmitted mechanically by harvesting or planting equipment
or other devices such as cane knives.
Chlorotic streak can infect a number of
common grass weeds.
Symptoms of chlorotic streak are irregular creamy white streaks sometimes with patches
of dead tissue within the streaks.
4 — Australian Sugarcane
Control
Chlorotic streak can be managed
through the use of disease-free planting
material and improved drainage of lowlying fields. Highly susceptible varieties
…6 s
August–September 2009
w4…CHLOROTIC STREAK
should not be planted in fields prone to the
disease.
Improved drainage will avoid water logging, which will reduce the risks of spreading chlorotic streak and improve cane
growth. In some low lying and flood prone
Red streaks running through the nodes of cane infected with chlorotic streak.
Figure 1: The influence of region on the incidence of chlorotic
streak disease in Queensland
areas, it is impossible to completely avoid
spread of chlorotic streak, therefore growers need to reduce the effects of the disease
by ensuring they use disease-free seed cane
and avoid highly susceptible varieties.
Seed cane should be planted on the
least flood prone and best drained section
of the farm to reduce infection. Approved
seed should be purchased regularly to renew a grower’s disease-free source of seed
cane. Approved seed is hot water treated
to ensure the seed cane is free of chlorotic
streak and other diseases such as ratoon
stunting disease and leaf scald. Chlorotic
streak can be eliminated from seed cane
by a short hot water treatment (50°C for
30 minutes). Growers should inspect their
seed cane or ask for their local Productivity
Service to inspect their seed cane.
If chlorotic streak is found in the seed
cane, the section of the block with the
disease should be avoided or a new seed
source that is free of disease located.
There is no reliable method to screen
varieties for resistance to chlorotic streak.
Varieties are rated for resistance to the
disease by experience over a number of
years in grower’s fields that are prone
to the disease. Some varieties are highly
susceptible to the disease and these varieties should not be planted in fields that are
prone to the disease.
If you would like further information on
chlorotic streak please contact your local
BSES extension officer. From BSES QCanes
Information sheet IS09004.
n
Average of 1980 to 2002 data. Source: Magarey, R (2006).
‘Disease Incidence: Regional Variation in Queensland’. Proc. Aust. Soc. Sugar Cane Tech. Vol 28.
6 — Australian Sugarcane
August–September 2009