Potato spindle tuber viroid (PSTVd)

PSTVd can affect more than potatoes

PSTVd is a pathogen that causes disease and potential loss of production, mainly in the Solanaceae family. That family includes potatoes, tomatoes, pepinos, and capsicum. It can also infect some ornamental plants, including dahlias, chrysanthemums, and petunias.

The viroid has been found in New Zealand in greenhouse tomatoes, capsicum, and in Cape gooseberry, and eliminated each time.

The last case was detected in 2022 at a commercial facility in Tasman. Our response to this infection was closed in February 2024 after destruction of infected crops, disinfection of the greenhouses, and extensive testing to confirm PSTVd had been eliminated.

PSTVd has been found in countries throughout the world, including in Europe, Central and South America, Africa, Asia, and Australia.

Many strains of the viroid exist, with symptoms ranging from asymptomatic to severe. (A viroid is like a virus but has a much simpler structure).

Why PSTVd is a problem for New Zealand

Depending on the strain, PSTVd can affect cropping plants, including potato, tomato, eggplant, and capsicum, potentially reducing crop yields.

Initial introduction of the viroid into potato and tomato crops is mostly through infected seed.

PSTVd is highly contagious. It is transmitted between plants through contact of the sap from small wounds in the leaf of a diseased plant to a healthy plant. This is done through:

touch
cutting or pruning tools
contaminated machinery
aphids from plants also infected with potato leafroll virus
infected potato tubers
pollen, but only to the seeds pollinated, not to the whole plant
potato and tomato true seeds.

How it can get here

PSTVd is most likely to arrive on seeds for planting or nursery stock.

An entry pathway was not found for the Tasman incursion in 2022. Seed samples from the batches of imported seed used for the affected plants tested negative for the viroid.

Biosecurity New Zealand has strict import conditions to limit the chances of PSTVd coming through the border.

How to identify PSTVd

Infected plants may show no signs of disease but have a lower than normal yield.

Visible signs in affected plants can include:

stunted plants
yellow or grey leaves.

In tomatoes, fruit may:

be small
have dead spots and streaks
not ripen normally
have reduced yields.

Affected potatoes are very spindly and small, with growth cracks.

In infected capsicum plants, the fruit is visibly unaffected, but the plant may have lower yields. The only visible sign is a mild distortion at the edge of leaves at the top of the plant.