Dry rot

''Fusarium solani var. coeruleum and Fusarium sambucinum'' are the two most common fungi causing dry rot of stored potatoes.

Symptoms
Fusarium dry rot is characterized by an internal light to dark brown or black rot and dryness of the potato tuber. The rot may develop at an injury such as a bruise or cut. The pathogen penetrates the tuber, often rotting out the center. Extensive rotting causes the tissue to shrink and collapse, usually leaving a dark sunken area on the outside of the tuber and internal cavities. Yellow, white, or pink mold may be present.

Several other diseases and physiological disorders, including Pythium leak, pink rot, late blight, and suboxygenation (blackheart), also cause brown to black internal discoloration of tubers. Leak and pink rot are wet rots; tubers exude a clear fluid when squeezed. Late blight is a less aggressive rot that generally does not penetrate into the center of the tuber and causes reddish-brown lesions. Poor air circulation or extremes in temperature that result in low internal oxygen concentrations can cause a smoky gray to black discoloration of tissue, but the tissue is never brown and is very firm.

Prevention
Avoiding bruising tubers is generally the best way to avoid dry rot. Avoid planting dehydrated tubers. Remove infected tubers from storage as soon as infection is detected.