Agriculture Reference
In-Depth Information
9
GRAPE
( Vitis spp.)
W i l d a n d c u l t i v a t e d g r a p e v i n e s b e l o n g t o t h e f a m i l y
Vitaceae and grape is the most widely planted fruit crop in
the world. Grapes were first grown in Australia soon after
the arrival of the First Fleet and vineyards were soon
established across southern Australia. Now, grapes are
grown in all Australian states and territories and grape
growing is the largest fruit industry in Australia. Wine
grape production is the largest sector of the industry
with more than 90% of production occurring in South
Australia, Victoria and New South Wales. The major grape
production areas are located in drier inland areas of the
continent as the environment in these areas favours the
production of high-quality fruit and is less favourable to
several important diseases.
Fig 9.1 Australian grapevine yellows (AGY) causes leaves to turn
yellow and curl downwards.
BACTERIA AND
PHYTOPLASMA
AUSTRALIAN GRAPEVINE
YELLOWS (AGY)
Cause
A phytoplasma, Candidatus Phytoplasma australiense .
Symptoms
Australian grapevine yellows (AGY) is most commonly seen
on the white varieties, Chardonnay and Riesling. From
f flowering onwards, AGY demonstrates four key symptoms:
shoots fail to harden-off, they are stunted, rubbery, bluish
in colour and die back from the tips; leaves turn yellow, curl
downward and fall prematurely; bunches die or berries
shrivel before harvest; and importantly, only some shoots
are affected on one or more arms of a vine. Entire vines are
rarely affected and most diseased vines recover next season.
Affected leaves develop irregular, yellow patches that may
later turn brown, especially in hot weather. Badly affected
shoots may die back to the spur, leaving a barren section
on the arm. The disease can be confused with shoot
damage where sap f low is disrupted by 'string disease'
or by wind-broken shoots. Some nutrient deficiencies
Fig 9.2 Leaf symptoms of Australian grapevine yellows (AGY).
(e.g. magnesium), herbicide damage (e.g. simazine), and
feeding by insects such as weevils have similar symptoms.
Source of infection and spread
Evidence to date suggests that AGY phytoplasma come
from outside the vineyard and are transmitted to vines by
sap-sucking leaf hopper insects that feed on specific native
shrubs. Different rates of transmission mean levels of AGY
vary from season to season. The disease does not spread
from vine to vine or in commercially significant levels via
cuttings from diseased vines.
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