By K. Frost and C. M. Ocamb
Potato (Solanum tuberosum) - Powdery Scab
Cause The Potato mop-top virus (PMTV) is a pomovirus vectored by the soilborne organism, Spongospora subterrenea, which causes powdery scab of potato. The virus can be found in scab spore-balls and can remain viable in the field 18 years or longer without the host. PMTV can also be tuberborne and thusly, can be in seed potatoes.
Until 2001, PTMV was considered an exotic pathogen, found primarily in cooler growing regions around the world. Currently, this virus is present in many potato production areas in the United States and is commonly found where powdery scab is present. Tuber symptoms are not commonly found but can increase in severity during storage. Yield losses due to PMTV can be up to 20% in highly sensitive varieties.
Symptoms Symptoms of PMTV infection vary depending on the variety and environmental conditions. Foliar symptoms may include yellow rings, V shape markings, and blotches, especially on the lower leaves but these foliar symptoms are not usually seen. Stems may also be stunted, giving a "mop top" effect. Tuber symptoms associated with PMTV infection include internal discoloration, brown arcs and rings, or flecks. These symptoms may not be present at harvest but may develop during storage. Tuber symptoms caused by PMTV infection can be confused with TRV or PVY infection and diagnostic tests are usually needed to determine the cause of tuber necrosis symptoms.
- Plant only certified potato seed.
- Do not move contaminated soil or equipment into clean fields.
- Genetic resistance has not been identified in commercial lines.