Potato mop-top virus B. D. Harrison Scottish Horticultural
Research Institute, Invergowrie, Dundee, Scotland Calvert &
Harrison (1966) and Harrison & Jones (1970). A virus with
straight tubular particles, occurring in small concentration in
tissue extracts, and transmissible by inoculation of sap. The
host range is narrow. The soil-borne fungus Spongospora
subterranea is a vector. Found in western Europe and South
America. In potato (Solanum tuberosum ), causes a wide range of
symptoms, which depend greatly on the cultivar and the
environmental conditions. The three commonest shoot symptoms are
yellow blotching or mottling ), particularly of the lower
leaves, chlorotic V-shaped markings in the leaflets ) and
extreme stunting of the shoots, known as mop-top Shoot symptoms
develop best in cool conditions (5-15°C). In the year of
infection from soil the tubers of some cultivars, such as Arran
Pilot, develop internal brown arcs (spraing) seen as brown rings
on the tuber surface The arcs develop at the boundary of