: any of several diseases of plants marked by dark often confluent lesions of the root and sometimes the crown often involving the whole cortex: as
a. : a disease of apples caused by a fungus (Xylaria mali)
b. : a disease of tobacco and various other plants caused by a fungus (Thielaviopsis basicola)
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Plant Pathol.
1. any of several diseases of plants characterized by black or brown lesions on the root.
2. a common disease of the apple caused by the fungus Xylaria mali.
3. a disease of tobacco caused by the fungus Thielaviopsis basicola and characterized by retarded growth and wilting.
[1905-10]
Useful english dictionary. 2012.