Pathogen. The fungus persists either in the soil or on infected seed tubers.
Disease development. Infection takes place through wounds or bruises at harvest or when grading. The rot
develops in storage. Disease incidence is higher when the soils are wet and cool at harvest.
External lesions are circular, slightly sunken, greyish-brown and the size of a thumb print. Underneath the lesions, the tissue is black, shrunken and decayed.Severe Phoma infection. Often cracks form on the surface of the lesions.The black, rotten tissue can be easily scooped out from the surrounding healthy tissue.
