Yellowing is a common sign of water-logged roots, and if accompanied by wilting may be due to drought.
Wilting of the foliage followed by the discoloration of the stem and branches is characteristic of a disease of the potato known as "Blackleg."
The principal features are the stoppage of the vessels and consequent wilting of the shoots; as a rule the cut vessels on transverse sections of the shoots appear brown and choked with a dark yellowish slime in which bacteria may be detected, e.g.
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