Verticillium wilt – Verticillium spp., fungus
This disease produces no external tuber symptoms, but causes a light brown discoloration in the vascular tissue of tubers, which may extend halfway through the tuber. Cavities sometimes develop inside tubers. Infected seed pieces often produce wilt–free plants, but soil adhering to tubers may contain the fungus and provide inoculum for infection of the subsequent crop. Pink eye, a pinkish or tan discoloration of the tuber surface around the eyes, may also develop on tubers produced from Verticillium–infected plants, but is caused by a bacterium, Pseudomonas fluorescens. Pink eye can be confused with the tuber rot phase of late blight. Because of the soilborne nature of Verticillium wilt, long rotations and the use of resistant potato varieties are recommended. Avoid late cultivation and hilling of susceptible varieties, for root pruning increases the risk of infection. The presence of the root lesion nematode, Pratylenchuspenetrans, greatly increases yield losses due to Verticillium wilt.