/ Dictionary / Index B black root rot: Meaning and Definition of Find definitions for: black' root' rot" Pronunciation: [key] — Plant Pathol. Plant Pathol. any of several diseases of plants characterized by black or brown lesions on the root. a common disease of the apple caused by the fungus Xylaria mali. a disease of tobacco caused by the fungus Thielaviopsis basicola and characterized by retarded growth and wilting. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Black Rod black rot Related Content Daily Word Quiz: lunar Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language