Fusarium Tuber Decay
Several Fusarium species are causative agents for disease in potato. The diseases are commonly classified as Fusarium dry rots and Fusarium wilts (see Diseases / Wilts / Fusarium Wilt). Each of these diseases are generally caused by different Fusarium species. Fusarium solani and F. roseum are mostly associated with dry rots.
Dry rot can be a problem on storing tubers for any market, but it is especially problem for seed tubers to be planted for the following season. Tuber lesions become visible about a month into storage. Small brown infected areas enlarge and the periderm (skin) over the lesion becomes sunken as the affected tissue drys out. Rotted tubers shrivel and mummify. Internally the rotted areas are light to dark shades of brown and contain cavities lined with visible fungus growth (pictures of Dry Rot on Red and White Skinned Tubers). With saturated relative humidity in storage the infected tubers are often further invaded by bacteria that cause a soft rot of the remainder of the tuber and spread to other adjacent tubers. A slight infection of tuber through movement of the fungus from the vine to the tuber may result in a vascular discoloration that turns brown during frying (picture of infected vascular ring). See Disease / Tuber Blemishes / Vascular Discoloration.
Infection occurs through wounds and at cut surfaces of tubers obtained during harvest and piling, and while being handled in storage. Infected seed pieces rot from the cut surface inward. Fusarium will entirely or partially destroy the planted seed pieces resulting in missing or small slow-growing plants that produce few marketable tubers.
Infection and development of dry rot in storage is most rapid at high relative humidity and, under those conditions, will continue even at the lowest temperatures for safe storage. Optimum temperatures for dry rot are reported to be 60-68 F. However, conditioning seed tubers from cold storage at that temperature before cutting pieces is suggested to reduce decay and accelerate sprout growth.
Control of dry rot is enhanced by:
1) harvesting tubers from dead vines,
2) avoid wounding and provide aeration during storage,
3) treat seed tubers before storage and during preparation for planting,
4) warm seed tubers at 60-68 F for one week before cutting or planting,
5) plant seed in soils warm enough for sprout growth and wound healing.
Dry rot in tuber vascular system
Dry rot on red skin tuber
Dry rot on white skin tuber