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What does dark streaking in the sapwood of a wilted branch suggest?
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Plant disease
Potato leaf infected with a fungal blight.
Dark streaking in the sapwood of a wilted branch is a diagnostic symptom indicating the presence of wilt-inducing microorganisms.2
These pathogens, which include various fungi and bacteria, invade and colonize the plant's water- and food-conducting vascular tissues. For example, in the case of Verticillium wilt, the sapwood just beneath the bark of an affected branch typically reveals these dark streaks when cut lengthwise.1
Because these symptoms are associated with the disruption of the plant's vascular system, they are distinct from non-infectious causes of wilting, such as environmental stress or mechanical injury.12