LOCALIZATION OF PHENOLIC-COMPOUNDS IN CROWNS AND ROOTS OF HEALTHY ANDRHIZOCTONIA SOLANI-INFECTED SUGAR-BEETS

A histochemical test employing nitrous acid, that produces red nitroso derivatives of some phenolic compounds, was modified for use in the f ield and was used to demonstrate localization of phenolic compounds in healthy and Rhizoctonia solani-infected sugar beet (Beta vulgaris) pl ants. Nitroso-reactive materials were present in petioles and around m ature crown cavities of healthy plants. They were absent from tap root s, except that they occasionally were observed in lateral root tissue contained within tap roots. Nitroso-reactive materials were localized in healthy tissues surrounding quiescent, but previously active rot le sions caused by R. solani, but were not found around actively developi ng lesions or in association with wounds. The intensity of staining di minished late in the growing season. Preformed phenolic compounds may be involved in prophylaxis against pathogens in petioles and crown cav ities and in active resistance against R. solani in sugar beet tap roo ts.