Hi I'm Melanie Weckert, I'm a research scientist with NSW DPI and I work at the National Wine
and Grape Industry Centre at Wagga Wagga.
Bacterial inflorescence rot of grapevines has become a bit of a problem in cool climate
regions of NSW.
It all started in Spring of 2006-7 in Tumbarumba.
Tumbarumba is a cool viticultural region in the southern NSW.
Growers were reporting necrotic legions in the leaves and shoots and then decaying inflorescences
that actually fell off reducing the yield by up to 60%.
What was causing this?
Was it a physiological problem, turns out it was a microbial disease.
To test for this we incubated the inflorescences, after a day we noticed an ooze appearing on
the diseased shoots.
This ooze proved largely to consist of bacteria.
Further testing proved the identity of the bacteria as Pseudomonas syringae pv.
Syringae.
Or as we say PSS.
We gave the disease a name bacterial inflorence rot or BIR.
So this bacterium is a well-known bacterium of many horticultural crops, but this was
the first time it had caused berry and bunch loss of grapevines anywhere in the world.
Analysis of the DNA from this bacterium showed that the Tumbarumba bacteria are more closely
related to bacteria from the Adelaide hills than the near-by horticultural region of Batlow.
It is an indication that this bacterium may of originated from the Adelaide hills.
When we inoculated potted grapevines leaves and rachises with the bacterium, it caused
BIR symptoms similar to those found in the field especially when the potted vines were
kept under very humid conditions.
The humid conditions are very important, you won't get this happening when you get a dry
spring.
The potted experiments also showed that the bacteria caused leaf legions that are highly
susceptible to the growth of the highly destructive botrytis infection.
This is a result really relevant to cool climate regions which often have botrytis bunch at
harvest.
We have estimated the disease cycle for this pathogen.
We think it starts with a leaf infection.
So bacteria from the environment land on the leaf.
The bacteria swim on the leaf surface, they have little furgella that allows them to swim
in water.
They then enter the leaf stomata, from there they move along the veins and the xylem of
the grapevines and are able in infect the new inflorescences.
The inflorescences die and fall off.
In the winter the bacteria over winter in buds, cordon wood and trunks.
It is interesting about the cordon wood because a number of people have has success by changing
from spur pruning to cane pruning, so this might be something that people can try.
We found that suckers in the vineyard can often be infected by the bacterium as well.
In spring new shoots are infected from the infected buds and if there is high humidity
that promotes the disease severity.
So that is the end of the disease cycle.
We are now investigating how different anti-bacterial agents such as copper products and biological
control bacteria might decrease this bacterial population throughout the year.
People tried copper sprays but not was not very successful and we probably think the
reason for that is the copper sprays will be targeting bacteria on the outside of the
vine and we have found the bacteria are actually inside the vine.
So we found that a soil drench of a copper spray chelated to an amino acid was able to
decrease the disease where spraying didn't seem to have to much effect.
As the bacteria overwinter in buds we hope that treatment over a number of years may
cause the bacterial population within the buds to decrease so that fewer bunches are
lost in the future.
Our NSW DPI PhD student Stewart Hall has studied the bacterial DNA and how it differs between
different cool climate regions.
Stewart has now isolated the bacterium from diseased grapevine inflorescences in other
cool climate regions.
My name is Stewart Hall and I have just completed my PhD under the supervision of Dr Melanie
Weckert.
And my project looked at the dispersion of the bacteria Pseudomonas syringae pv.
Syringae across cool climate Australian vineyards.
So recently a disease causing extensive wine grape yield losses was reported in some cool
climate vineyards such as Tumbarumba, Coonawarra and Pipers river region.
This disease was called bacterial inflorescence rot and is caused by Pseudomonas syringae
pv.
Syringae and leads to the death of young grape bunches.
So what my PhD demonstrated that there was a distinct genetic strains of Pseudomonas
syringae pv.
Syringae and these were isolated from these diseased vineyards and I also found out that
the photophilic and genomic analysis I performed on these isolates produced particular toxins
and characteristics.
Finally my PhD also look into the defence genes studies of grapevines that were inoculated
with Pseudomonas syringae pv.
Syringae and this provided a unique insight into the grape defence responces.
On the basis of our study we conclude that the presence of Pseudomonas syringae pv.
Syringae in Australian cool climate vineyards may pose a threat to the Australian wine industry.
Damage from this bacterium can cause severe economic losses.
In the Vineyard protective measures against this bacterium may need to be considered because
it is so easily dispersed through pruning and other equipment.
People who have helped us with this project are the DPI extension offices Leo Kuirk and
Kevin Dodds.
The vignerons society at Tumbaruma have been very helpful and Wine Australia provided top
up funding for Simon Halls PhD project and Tom Hill and Nathan Scarlett collected some
of the inflorescences from South Australia.
Thank you