Potato mop-top virus (PMTV)

Potato mop-top virus (PMTV) is a plant pathogenic virus transmitted through the vector Spongospora subterranea, the organism that causes powdery scab in potatoes. Powdery scab occurrence is associated with wet and humid conditions, specifically poorly drained soil.

PMTV can lead to a very significant loss in the yield of potatoes. For example, a study conducted on Scottish seed potatoes showed a yield reduction as great as 67%. The virus also causes spraing and necrosis in the flesh of tubers. These symptoms are mainly morphological defects that yield unaesthetic potatoes which face commercial rejection from processors and packers.

Occurrence

PMTV is widespread in parts of both North and South America, and can remain alive for up to 18 years in soil within spores or in host plants. It has also been found in parts of Europe, especially in Scandinavia.

Detection

Visual inspection of plants or tubers may be inconclusive for PMTV because the symptoms are similar to responses caused by other viruses or physiological conditions. In addition, foliar and tuber symptoms may not be present. The most reliable methods for accurately determining the presence of PMTV include: isolation of the virus using soil and bait plant methods, and detection through the use of indicator plants.

Control

Generally any control measure against powdery scab will also help to control PMTV e.g. using resistant varieties, long rotations, clean seed on clean land and promoting good drainage. In the absence of the vector, transmission from mother to daughter tubers is, depending on variety and conditions, incomplete, and so is self eliminating. Together with roguing of symptomatic plants the infection can be eliminated from stocks in a few generations.