Potato mop-top virus

The disease is caused by the virus Pomovirus solani.

Internationally, 2 PMTV strain categories have been identified: 'severe' and 'mild'. The strain of PMTV detected in Tasmania is unknown.

Symptoms

Tubers

• Rust-brown, arc-shaped internal discolouration, often forming rings.
• Deep cracking or distortions of the skin.
• Necrosis or rotting of tuber flesh.
• Russeted skin with net-like patches.
• Uneven distribution of symptoms between tubers, even within the same plant.

Some tuber varieties may have internal symptoms only, while others may have skin symptoms only. Also, some tubers may have no symptoms, depending on the variety and disease severity.

Symptoms may be worsened by sudden or prolonged temperature drops. However, tuber symptoms do not typically worsen during storage.

Leaves and stems

• Yellowing, mottling or V-shaped patterns on leaves.
• Leaf vein clearing (veins becoming translucent or yellow).
• Leaf distortion and curling ('mop-top' appearance).
• Stunted growth with closely bunched upper leaves.

Foliar symptoms are rare and inconsistent. They typically appear only if infection comes from infected seed potato tubers.

Symptoms are more noticeable in cool, wet conditions. They fade as the weather warms.

• Tobacco rattle virus causes symptoms very similar to those of PMTV. Laboratory testing is needed to distinguish it from PMTV.
• Internal rust spot produces brown discolouration in tubers similar to PMTV infection, but this is a physiological disorder not caused by disease.
• Potato powdery scab (Spongospora subterranea f. sp. subterranea) without PMTV infection can cause symptoms on the surface of potato tubers that appear similar to symptoms of PMTV.

PMTV is present in Asia, Europe, North America, New Zealand and South America.

It is widespread in Tasmania (first reported in 2025), but has not been detected in potato plants in other Australian states and territories.

Potato powdery scab, the vector for PMTV, is present in most Australian potato-growing regions except seed potato protected areas (PDF, 378KB) in New South Wales.

The primary host of PMTV is the common potato (Solanum tuberosum). Only species in the Solanaceae and Chenopodiaceae families are hosts of PMTV.

Sweetpotato (Ipomea batatas) is not a host of PMTV.

Natural hosts

• Common potato (Solanum tuberosum)
• Black nightshade (Solanum nigrum)
• Fat hen (Chenopodium album)

Potential hosts

• Capsicum (Capsicum annuum)
• Ground cherry (Physalis spp.)
• Jimsonweed (Datura stramonium)
• Petunia (Petunia spp.)
• Sugar beet (Beta vulgaris)
• Tomato (Solanum lycopersicum)

• PMTV persists in the resting spores (cystosori) of potato powdery scab in soil for many years, even in the absence of potatoes.
• When a new potato crop is planted, the resting spores germinate under cool, wet conditions, infecting roots and tubers, and introducing PMTV into the plant.
• The fungus forms new resting spores containing PMTV on infected tubers and roots, allowing the virus (within the fungus) to persist in the soil.

• Yield losses can be highly variable, ranging from minimal to significant (for example 67%) depending on the potato variety and growing conditions.
• PMTV symptoms can lead to rejection or downgrading of tubers by fresh food and processing markets.

Vector

In nature, transmission of the virus is through vectoring by potato powdery scab.

Potato powdery scab effectively vectors PMTV between plants in fields and from season to season in resting spores. PMTV can survive in resting spores of potato powdery scab for more than 12 years, even without common potato crops being present.

Cool, wet conditions favour potato powdery scab infection and therefore increase transmission of PMTV between plants in infected crops.

Transmission pathways

• Contaminated soil, including on farm equipment, tools, boots and machinery.
• Infected seed potato (tubers used for seeding new crops).
• Water or any material carrying contaminated soil or infected potato powdery scab resting spores.

• Do not touch or move infected plant material or soil because this could spread the disease further.
• Practise good biosecurity measures on your property.
• Source disease-free planting material such as certified seed potato tubers from reputable suppliers.
• Use thorough hygiene practices such as disinfecting tools, propagating equipment and vehicles.
• Train staff and visitors to ensure they follow your biosecurity requirements.
• Monitor your crops regularly for disease.
• Remove wild or volunteer potato plants and other weeds such as nightshade that could act as reservoirs for the virus.
• Report symptoms that resemble PMTV infection immediately using 1 of these methods
  • Report online
  • Phone Biosecurity Queensland on 13 25 23
  • Phone the Exotic Plant Pest Hotline on 1800 084 881.

• Protecting your farm
• Farm biosecurity
• Potato growers' biosecurity manual (PDF, 2.9MB)

PMTV is biosecurity matter under the Biosecurity Act 2014.

Under the Act, everyone in Queensland has a general biosecurity obligation (GBO) to report biosecurity risks and take action to prevent or minimise them.