Symptoms on tuber

On the tuber surface, the infected tissues turn brown (photo 1) and shrivel (dehydration), and may even show concentric streaks sometimes with pinkish to whitish mycelium (photo 2).

When cut in half, the tuber reveals a brown rot which develops into the flesh, with an unclear limit between healthy and infected areas, and with the potential presence of internal cavities covered with mycelium (photos 3 and 4). The tuber may dry out gradually, eventually becoming hard and mummified.

Under humid conditions, Fusarium-infected tissues can be readily invaded by secondary micro-organisms, such as bacterial soft rot, which can cause an extremely rapid wet decay.

Dry rot caused by Fusarium spp. (photo 5, bottom tubers) is usually not as dry as the depressed rot caused by Phoma (gangrene), (photo 5, top tubers).