Gangrene

Gangrene (Phoma exigua var. foveata.) is a disease of potato tubers occuring during storage.

Symptoms
Symptoms first appear as small dark depressions associated with wounds, eyes or lenticels. The depression can enlarge to form larger irregularly shaped areas. Gangrene also causes an internal rot beneath the superficial depressions, which is characterised by extensive cavities with walls which are discoloured and lined by dark grey or pinkish-purple strands of the fungus. The extent of the internal rots is not related to the size of the diseased area on the surface, and it is common to find relatively minor surface damage masking extensive internal damage.

Treatment
None. Destroy infected tubers immediately.

Prevention
Only plant uninfected seed potatoes bought from a reputable source. Be careful not to damage tubers when checking the crop or harvesting. Harvest potatoes soon after defoliation, especially during cold periods. If possible, cure potatoes at 16-20°C (60-68°F) for one to two weeks after harvest. Curing aids in the healing of tubers, which is slower at colder temperatures.