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INTERNATIONAL R&D | ZEBRA CHIP |
Zebra chip disease has severely impacted potato
industries in both the United States and New Zealand.
To combat this, the Texas A&M AgriLife Research
pathology team is investigating the possibility of
developing a potato variety that is resistant to the
disease. Plant pathologist Dr Charles Rush spoke to
Potatoes Australia about the research.
ENCOURAGING RESEARCH
IN THE BATTLE AGAINST
ZEBRA CHIP
Zebra chip disease, which stems from the bacterium Candidatus
Liberibacter solanacearum (and is vectored by the tomato-potato
psyllid; Bactericera cockerelli) was first identified in the United
States in 2000.
Zebra chip then spread to the seed production regions of
Colorado and Nebraska and in 2011, the disease was detected in
the Pacific Northwest region of Washington, Idaho and Oregon,
where the majority of all potato production in the United States is
grown. Fortunately, it has not yet been found in the eastern part
of the country.
VARIETY SCREENING
In 2016, Texas A&M AgriLife Research Plant Pathologist Dr Charles
Rush and his team undertook variety screening of potatoes with
resistance to zebra chip.
“The research focus of my lab is on pathogen/vector ecology
and plant disease epidemiology (dealing with the incidence and
distribution of diseases), but we also work on disease control and have
worked with breeders in evaluating their germplasm,” Dr Rush said.
“We have worked with the Texas Breeder Creighton Miller (who is
now retired) as well as a US Department of Agriculture-Agricultural
Research Service scientist, who primarily works on wild relatives of
commercial potatoes looking for traits and genes of interest.
“Progress is being made and it is clear some lines are much more
resistant to the disease and less favoured by the vector than other
lines, but all commercially available germplasm is susceptible to
zebra chip.”
Despite this progress, Dr Rush said that there are currently no
commercially acceptable zebra chip resistant cultivars, either
resistant to the bacterial pathogen or to the vector.
“Some of the lines we’ve evaluated show very little internal tuber
disease symptoms when fresh cut but they still exhibit defects when
fried,” he said.
“This means that the breeders are finding certain types of resistance
to actual disease progression in the tubers, but the tubers are still
infected with the pathogen and show defects when processed.”
A LONG PROCESS
Research into zebra chip resistant cultivars is continuing, however
Dr Rush said results won’t occur overnight.
“These are typical results for breeders seeking to identify resistance
to almost any new plant pathogen. Progress is incremental –
but clear progress is being made so everyone keeps working.”
According to Dr Rush, if zebra chip resistant potato varieties
were discovered, it would save the potato industry millions of
dollars each year.
“Farmers currently are treating almost every week to 10 days to
control the tomato-potato psyllid so not having to do that would
be beneficial both from an economic and an environmental
standpoint,” he said.
“In our experience, the bacterial pathogen is usually only
detected in about three per cent of the psyllids captured on
sticky traps (in regional surveys) but this level can result in
significant disease if not managed.”
Local and international collaboration is essential when dealing
with a highly destructive potato pest, and this has proved beneficial
in the case of tomato-potato psyllid.
“Scientists from New Zealand came to the United States each
year and several collaborative studies were initiated between the
two countries,” Dr Rush explained.
“I think growing conditions in some parts of Texas and other
production areas in the United States are very similar to Australia and
information generated will be of great value and application
to Australian scientists and growers alike.”
OPTIMISTIC FUTURE
Dr Rush offered a word of hope to Australia’s potato growers, and
said that while zebra chip is certainly a very serious and potentially
damaging disease, it can be managed.
“It will be very important to monitor psyllid populations and get a
good idea of where they come from, when they show up in growers'
fields and if they are carrying the bacterial pathogen. It is also
important to be timely with vector management and not fall behind.”
For more information, please contact Dr Charles Rush at
or visit
This communication has been funded by Horticulture Innovation Australia
using the fresh potato research and development levy and funds from the
Australian Government.
Project Number: PT15007
INFO
R&D | BIOSECURITY BRIEF |
As this issue reaches readers of Potatoes Australia, the tomato-potato psyllid
incursion in Western Australia will be in its fourth month. As noted in the previous
Biosecurity Brief, eradication was not regarded as technically feasible and we are
now at the end of the first month of a transition to management program.
AUSVEG Biosecurity Adviser Dr Kevin Clayton-Greene explains what this means.
TOMATO-POTATO PSYLLID: BIOSECURITY UPDATE
Transition to Management (T2M) was agreed and approved
by all parties in 2016 and is “the undertaking of activities for
transitioning the management of an EPP (Emergency Plant
Pest) from seeking to achieve eradication of the EPP during an
Emergency Response Phase to management of the EPP outside
the EPPRD (Emergency Plant Pest Response Deed)”.
In other words, it is a program that can be cost-shared by all
parties to the incursion (government and industry) to help these
parties manage the pest going into the future.
This can include a range of activities such as addressing market
access issues, ongoing control to minimise further spread,
developing on-farm strategies to reduce impact at the farm
level and also preparing other areas in the country, outside of
the current incursion, should the pest spread further. Typically
activities included under a T2M plan would be:
• Potential control options including new chemical registration.
• Building capacity in the industry and community around
pest management.
• Developing an understanding of the pest’s behaviour.
• New government regulations or legislation.
• Codes of practice review and development.
• Communication, training and engagement.
A NEW APPROACH
This is a relatively new addition to the Plant Health Deed and is
a result of a working group set up by Plant Health Australia to
investigate how T2M could be prosecuted under the existing
Deed. It had been recognised for some time that there was a
significant gap in the Plant Health Deed: once a pest was deemed
beyond eradication, there was no formal mechanism to cover the
question of ‘what happens now?’
The tomato-potato psyllid (TPP) incursion is one of the initial
incursions that is using this new provision of the Deed. A T2M
plan can have a maximum timeframe of 12 months under the
Deed, after which all parties are then expected to manage the
pest themselves.
As with an eradication response, a T2M Response Plan has to
be prepared and the budget approved by all parties. Preparation
of the plan is the responsibility of the host state and in the case of
TPP, this is Western Australia.
ZEBRA CHIP TESTING
Of particular interest in the TPP incident is whether or not the
psyllids are also carriers of Candidatus Liberibacter solanacearum
(CLso), which causes zebra chip and is fatal to many solanaceous
plants. Thus a key part of the T2M plan will be ongoing testing of
psyllids to determine if there is any CLso present.
It has been agreed that this should extend over two seasons
and if no CLso has been detected after such a comprehensive
testing regime, then Western Australia and perforce Australia
can make a claim for area and country freedom. The current
surveillance for CLso is by sampling TPP, as the technical advice
at present is that this is the most reliable method.
In plant parts and potato tubers, it can take some time (up to
three weeks) for CLso to be distributed and sampling of plants
parts may yield a false negative. Potato tubers are problematic
as the bacteria is not uniformly distributed in the tuber even
when present.
The current plan is to recommence with TPP testing once
numbers ‘increase’ in summer when obtaining sufficient
numbers is not too problematic.
It will be important for the industry in Western Australia to
get behind the CLso surveillance program, otherwise it will fail
to achieve its objectives.
For more information, contact AUSVEG on 03 9882 0277 or
email .
This communication has been funded by Horticulture Innovation Australia
using the fresh potato research and development levy and funds from the
Australian Government.
Project Number: PT15007
INFO