Dry rot of potatoes may be caused by the fungi Fusarium solani "Coeruleum" or F. roseum "Sambucinum" (F. sambucinum f.6 = F. sulphureum) and occasionally by F. roseum "Avenaceum". These fungi are soil-borne and survive in soil on plant debris or on the potato tuber surface.
Tubers with mature skins and that are harvested without wounding are most resistant. Infection occurs when tubers are wounded during harvest, grading and seed piece cutting operations. In storage, disease symptoms begin as small brown areas near wounds which eventually enlarge creating sunken wrinkled areas as tissues dry out. Sometimes secondary invaders (e.g. bacteria) create a wet rot.