Tuber Internal Growth Defects: VASCULAR DISCOLORATION

Vascular rin discoloration on chipsNon-pathogenic vascular discoloration is associated with low soil moisture and rapid, 1-3 days, vine death due to acid, frost, or mechanical kill. High temperature stress at vine kill increases the severity of the disorder.

External Appearance:

There is no outer change of appearance.

Diagnostic Method:

Slice transversely from stem end.

Internal Appearance:

Disorder is characterized by a light tan to reddish brown speckling or a dark brown streaking in the vascular tissue. The speckling or streaking usually extends to about a half inch from the attachment point, but in severe cases may extend in the vascular system the length of the tuber. This disorder is readily mistaken for vascular discoloration due to Verticillium wilt or leaf roll net necrosis (pathogenic causes).

Cooking Appearance:

Specks remain dark after boiling and baking. Chips from stem end will have a brown ring near their edge. Fries will have a brown band just below the stem-end cut.


Tubers near full maturity are most susceptible. The disorder may be seen in the field before harvest and develops during the first two months of storage.

Control Measures:

  1. Irrigate prior to vine desiccation.
  2. Desiccate vines gradually, 1-2 weeks for complete kill.