PSTVd can affect more than potatoes
PSTVd is a pathogen that causes disease and potential loss of production, mainly in potatoes, tomatoes, pepinos, and capsicum. It can also infect some ornamental plants, including dahlias, chrysanthemums, and petunias.
The viroid has been found twice before in New Zealand in glasshouse tomatoes and capsicum, and in Cape gooseberry. It was eradicated both times.
This plant pest has been found in many parts of the world, including Europe, Central and South America, and Africa.
Many strains of PSTVd exist, with symptoms ranging from asymptomatic to severe infections. The incursion near Nelson, in the Tasman district, appears to be a mild strain of the disease.
A viroid is like a virus but has a simpler structure.
Why this 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:
- 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
Potato spindle tuber viroid is most likely to arrive on seeds for planting or nursery stock.
An entry pathway has not been found for the Tasman incursion. Seed samples from the batches of imported seed used for the affected plants have tested negative for the viroid.
Biosecurity New Zealand has strict import conditions to limit the chances of PSTVd coming through the border.
The viroid has not been found at any New Zealand locations other than the one affected commercial operation in Tasman.
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.
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.
Images of how the viroid affects potatoes
Images of tomato plants infected with PSTVd
Report suspected cases of PSTVd
Freephone Biosecurity New Zealand's Exotic Pest and Disease Hotline 0800 80 99 66 to report suspected cases of PSTVd.