Changes in chemical composition related to fungal infection and induced resistance in carnation and radish investigated by pyrolysis mass spectrometry

Abstract

Pseudomonas fluorescens WCR 417r induces systemic resistance in radish roots challenged by Fusarium oxysporum f. sp. raphani and, incidentally, in carnation stems challenged by Fusarium oxysporum f. sp. dianthi. The induced systemic resistance is not associated with accumulation of pathogenesis-related proteins (PRs) or, at least in case of radish, with increased peroxidase activity. We tested whether the induced systemic resistance might be associated with changes in the host cell wall composition. Cell wall degradation, using pyrolysis mass spectrometry, was demonstrated on fungal infection in carnation and probably in radish as well. Lignin was found to be demethoxylated, oxidized and depolymerized. In carnation both syringyl and guaiacyl lignin were broken down. In radish root probably mainly syringyl lignin was degraded. Cellulose and hemicellulose were degraded in carnation and possibly in radish. Bacterization with P. fluorescens WCS 417r prior to fungal infection reduced such cell wall degradation, consistent with its resistance inducing action. In the case of the radish roots it seems very improbable that this reduction is a necessary component of the induced fungal resistance. For carnation it remains to be investigated.