Root canker

Black or orange patches on the roots are a sign of parsnip canker. The patches usually occur near the shoulder of the roots and the crown of the plants. In severe cases, the roots crack and rot. There are two kinds.
Black Canker, which is, in fact, tinged purple. It is considered to be mainly caused by a fungus. Brown or Orange Canker, is thought to be caused by invasion of the fungus Itersonilia pastinacae. It is not usually damaging, but it gets into damaged roots. It is also responsible for leaf-spot disease.