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Biosecurity
Department of Primary Industries, Parks, Water and Environment

Home > Biosecurity > Plant Health > Potato Virus Testing

Potato Virus Testing

Colour close up photograph of seed potato tubers.Background
Virus Sampling
Sample Results
What Needs to be Done?
Virus Symptoms
Further Information

Virus Strategy Group

To meet concerns about Tasmania's ability to detect potato virus, and following increased reports of virus on the mainland, the then Department of Primary Industries and Water (DPIW) convened a committee of industry stakeholders to address the problem. This committee, known as the 'Virus Strategy Group', has representatives from all sectors of the seed industry and includes:
  • Processors, (Simplot Australia Pty Ltd and McCains Foods (Australia) Pty Ltd)
  • Fresh markets companies (Harvest Moon)
  • Processing seed grower representatives
  • Fresh market seed grower representatives
  • DPIPWE Certification staff and Industry Development officers
  • Tasmanian Institute of Agriculture (TIA) researchers
  • Tasmanian Farmers and Graziers Association’s (TFGA) Industry Development Officer.
The committee decided that it was essential to establish if any virus existed and resolved to carry out a comprehensive survey of all seed potato crops in the State. In addition, the committee recommended the investigation of a number of strategies to reduce the impact of virus infections.Go to top of page

Background

Tasmania's potato industry has been largely virus free for several decades. This is believed to be partly due to the State's isolation, but also to its strict adherence to the Tasmanian Certified Seed Potato Scheme.

The Tasmanian Certified Seed Potato Scheme was introduced in the 1920s to ensure varietal purity, and to control the seed-borne viruses that devastated crop yields several decades ago. This was successfully accomplished through the operation of the Scheme. The scheme works on a flow through basis, in which minitubers are produced from virus free tissue culture stock. This stock is then multiplied through a maximum of five field generations before it is used to produce a commercial crop. A full ELISA virus test is carried out if seed certification officers observe any visual virus symptoms during field inspection of seed crops. Any crop with greater than 1% infection is rejected for use as certified seed.

Early in the potato season (2001/2002), McCains Foods (Australia) Pty Ltd carried out some routine virus testing on a number of their seed crops throughout the State. Several of these tests returned a positive result for three different viruses, Potato Virus S, (PVS) Potato Virus X (PVX) and Potato Leaf Roll (PLRV).

Virus Sampling

DPIW Seed Certification officers and field officers from the two processing companies carried out the sampling for the virus survey. Samples of 40 leaves were collected from every certified seed paddock in the State. Wherever possible, plants showing disease symptoms were targeted.

The samples were sent to DPIW laboratories in New Town where they were analysed for the presence of the three different viruses. The sampling and testing procedure indicated only the presence or absence of the diseases in the paddock, and did not give a measure of the level of infection. DPIW staff compiled the results from the survey.

Sample Results

Table 1 – Results of virus testing in Tasmania in 2002.

Virus
Percentage of crops tested with virus present
Potato Leaf Roll Virus (PLRV)
7%
Potato Virus X (PVX)
7%
Potato Virus S (PVS)
31%

See additional details for information on these viruses, their symptoms and effects.

Prior to 1999, all certified seed crops grown below 180 m altitude required mandatory virus testing to comply with the seed scheme. At the request of the industry, this requirement was waived in 1999, as none of the crops below that altitude were returning positive results and the costs to growers were considered a burden.

The results from this season's survey indicate a significant increase in the level of virus infection around the State (over the last few years), and as such, a coordinated response is required to tackle the issue.

The first questions raised by the survey results were: Where has the infection come from? and What has caused the increase in disease incidence?

The potato industry has been concerned for some time about the rapid spread of unregistered potato varieties that are not reproduced under the Seed Certification Scheme. Many home gardeners and growers for the fresh market have been growing potatoes using uncertified seed sources including unregistered varieties of doubtful origin. The production of varieties that do not come under the certification scheme in traditional seed growing areas is likely to be a significant factor in the spread of viruses. It has been known for some time that the variety Dutch Cream (which is not certified under the Scheme) contains PVS and PVX. The Department has been attempting (without success to date) to clean the virus out of this variety so that it can be introduced into tissue culture and therefore into the seed scheme. The production of this variety is a significant threat to the virus status of the Tasmanian potato industry.

The other factor that may have contributed to the spread of PLRV around the State is the increased use of insecticides to control thrips (the vector for Tomato Spotted Wilt Virus) particularly in the Derwent Valley. This may have lead to a reduction in the number of beneficial insects in those areas and resulted in an increase in the number of aphids, leading to the spread of PLRV.Go to top of page

What Needs to be Done?

The Potato industry in Tasmania is worth approximately $95 million at the farm gate, and the risk of reductions in yield due to the spread of these viruses poses a threat to the industry that cannot be ignored. The industry stakeholders working through the Virus Strategy Group are acting to implement a series of steps to firstly determine the risk posed to the industry, and secondly, what steps need to be taken to minimise that risk. These steps include:
  1. A more comprehensive series of testing of all seed stocks during next season. This will indicate not only presence or absence, but also overall percentage within each crop.
  2. Investigate the impact of PVS and PVX on yield, both in isolation and in combination with other viruses under Tasmanian growing conditions.
  3. Determine the transmissibility of each virus under the Tasmanian seed handling regime. Depending on the outcome of this work a further series of measures may be required to limit the impact of these viruses within the State. These might include:
    1. Regulating the movement of seed around the State.
    2. The compulsory virus testing of commercial crops which are to be retained as seed (known as "approved" seed).
    3. The introduction of a farm hygiene program and a grading, handling and storage program to reduce the spread of the mechanically transmitted diseases.
    4. Changing the seed certification rules as they apply to Tasmania to further restrict the level of virus permitted in seed crops of different generations.
    5. Isolating the location of early generation crops to reduce their exposure to virus.
The Department, the TFGA and the two potato processing companies, Simplot Australia and McCain Foods (Australia), believe that the levels of virus detected in seed crops this year should not be a major cause of concern for growers at this stage. Early detection will allow appropriate measures to be put in place to reduce the incidence of virus in seed crops and subsequent commercial crops.
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Potato Virus Details 
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