Localization of phenolic compounds in crowns and roots of healthy and Rhizoctonia solani-infected sugar beets

Abstract

A histochemical test employing nitrous acid, that produces red nitroso derivatives of some phenolic compounds, was modified for use in the field and was used to demonstrate localization of phenolic compounds in healthy and Rhizoctonia solani-infected sugar beet ( Beta vulgaris) plants. Nitroso-reactive materials were present in petioles and around mature crown cavities of healthy plants. They were absent from tap roots, 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 lesions caused by R. solani, but were not found around actively developing lesions or in association with wounds. The intensity of staining diminished late in the growing season. Preformed phenolic compounds may be involved in prophylaxis against pathogens in petioles and crown cavities and in active resistance against R. solani in sugar beet tap roots.