When it comes to diseases caused by viruses, Tasmania's potato industry benefits from the State’s isolation (maintained by strict potato import requirements), and its rigorous 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 tuber-borne viruses that once devastated crop yields. The
scheme works on a flow through basis, in which minitubers are produced from virus-free tissue culture stock. This seed is then multiplied through a maximum of five field generations before it is either processed or sold through retailers.
Visual inspections and testing monitor virus levels, and the absence or near absence of virus (usually < 1% infection) ensures that the material is suitable for seed for the next generation.
Without the scheme's regular crop inspections and testing, virus levels would soon reach high levels resulting in inferior seed and subsequent lower-yielding disease-affected crops – impacting on the entire industry.
Testing
Plant Diagnostic Services, located at NRE Tas New Town Laboratories, undertakes virus testing of potato crops on request from growers and regulators.
The suite of viruses requested varies depending on the major issues perceived during each season, and have included combinations of:
Potato virus S (PVS)
Potato virus X (PVX)
Potato virus Y (PVY) including necrotic strains
Potato leaf roll virus (PLRV)
Potato virus A (PVA)
Potato mop top virus (PMTV)
Tomato spotted wilt virus (TSWV)
Alfalfa mosaic virus (AMV)
The testing is conducted using either PCR (Polymerase Chain Reaction) or ELISA (Enzyme-Linked ImmunoSorbent Assay). PCR is the most sensitive and works well with tubers, whilst ELISA is generally best suited to leaf testing.
Sampling
Typically, sampling of a seed crop has consisted of 300 leaves collected randomly, via a transect pattern, and submitted/tested as either 15 lots of twenty leaves, or 30 lots of ten leaves (subject to variation). A percentage infection for that crop can then be calculated on the number of positives detected.
Single or small numbers of symptomatic samples, either leaves or tubers, are also submitted to diagnose diseases observed in the field.
Governance
The Tasmanian Certified Seed Potato Scheme is overseen by the Tasmanian Institute of Agriculture (TIA) through TasSeed. Together with key industry stakeholders, TIA research scientists make decisions on sampling regimes and the viruses to be tested each season – based on which viruses are considered to be the most important at the time.