Potato mop top virus (PMTV)
Potato mop top virus (PMTV, Pomovirus solani) is a plant virus transmitted by the soil-borne fungus Spongospora subterranea, which also causes powdery scab in potatoes.
Potato mop top virus was first identified in Britain in 1966 and has since spread globally, with significant detections in North America during the 1990s, in New Zealand in September 2018, and most recently in Tasmania in August 2025, marking its first appearance in Australia.
The virus mostly affects potatoes (Solanum tuberosum) but tomatoes, black nightshade and ground cherry can also be hosts.
Regions with cool, wet conditions are more vulnerable due to the favourable environment for S. subterranea.
Though it poses no food safety risk to humans, potato mop-top virus can cause significant yield and quality reductions in potatoes.
Identification
Tuber symptoms, which are called "spraing" are the rust-brown discoloration in the shape of arcs or rings that appear internally on the potato. Spraing usually appear more after harvest and when the potatoes are stored but overall tuber symptoms are not commonly found.
- Leaf and stem symptoms only appear if the seed planted is infected.
- Symptoms vary depending on weather and season.
- Leaf and stem symptoms are favoured by cool weather and may fade as the season becomes hotter.
- A yellow pattern can appear on the lower leaves or as a V-shaped pattern or internode shortening (mop-top).
No results were found
Spread
- Soil movement – the fungal vector can be spread through contaminated soil, farm equipment, seed potatoes, and water.
- Seed potatoes – infected but symptomless tubers can introduce the virus to new areas.
Management
- Planting certified seed potatoes reduces the risk of all potato diseases, including PMTV and powdery scab.
- Good weed management minimises the possibility of wild hosts acting as a reservoir for the virus.
- Once both vector and virus are established in a field, PMTV is difficult to eradicate.
Import restrictions
Certain measures are required when importing potential host products of potato mop-top virus into South Australia.
Host products include:
- seed potatoes, ware potatoes (for eating), potatoes for processing
- soil, agricultural machinery, equipment.
- diagnostic samples (plant or soil).
These are outlined in Condition 31 ( ) of the Plant Quarantine Standard.
Exotic Plant Pest Hotline
Suspected plant diseases, exotic pests, or noxious weeds must be reported immediately.
Call us if you find plant pests or diseases that could be a national threat, even if you are unsure.
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