Potato mop-top virus

PMTV originated from the Andean region of South America and has been reported in Canada and several U.S. states, including Maine, North Dakota, Washington, Idaho, New Mexico and Colorado. It is also found in the United Kingdom, Ireland, Great Britain and the Nordic countries in Asian countries in Japan and China.

Biology

PMTV belongs to the genus Pomovirus within the family Virgaviridae. The virus has three single-stranded RNA segments. RNA1 encodes RNA-dependent RNA polymerase, RNA2 contains the coat protein (CP) and RNA3 harbors a triple gene block (TGB) which facilitates cell-to-cell and systemic movement. PMTV is transmitted by a soilborne protozoan called Spongospora subterranea f. sp. subterranea (Sss), which also causes powdery scab in potatoes. The virus can persist in the soil for up to 18 years within the resting spores of its vector.

Symptoms

The most notable symptom is tuber necrosis, characterized by dark brown, necrotic arcs or lines within the tuber flesh, commonly referred to as "spraing." PMTV rarely causes symptoms on the leaves.

Damage

Infected plants show reduced yields and tuber quality, significantly impacting potato production.

Management

Managing PMTV involves rotating potatoes with non-host crops to reduce virus and vector buildup, avoiding over-irrigation to prevent the vector Spongospora subterranea from thriving, and maintaining sanitation by cleaning equipment and avoiding soil movement from infected fields. Controlling the vector includes using certified seed potatoes free from powdery scab and applying soil treatments judiciously. Soil testing and certified seed help manage PMTV by detecting the virus’s soilborne vector and preventing the introduction of infected planting material. Additionally, planting resistant potato varieties, as recommended by research and extension services, is crucial for effective management.

Further readings

• Potato mop-top virus: Biology and disease management, BUL 1017
• Compendium of potato diseases, 2nd edition

Pesticide warning

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Trade names — To simplify information, trade names have been used. No endorsement of named products is intended nor is criticism implied of similar products not mentioned.

Groundwater — To protect groundwater, when there is a choice of pesticides, the applicator should use the product least likely to leach.