Localization of phytoalexin accumulation and determination of changes in lignin and carbohydrate composition in carnation (Dianthus caryophyllus L.) xylem as a consequence of infection with Fusarium oxysporum f. sp. dianthi, by pyrolysis-mass spectrometry

Minute pieces of xylem and other tissues from stems of healthy and fungus-infected plants of two carnation cultivars Novada and Lena were investigated for lignification (lignin/polysaccharide ratios) and lignin composition by means of pyrolysis mass spectrometry and pyrolysis gas chromatography mass spectrometry. This technique proved also very effective for the localization of dianthramide phytoalexins which accumulate in carnation after infection with Fusarium oxysporum f.sp. dianthi. The composition of healthy tissues from both cultivars was practically the same. In the resistant cultivar Novada, infection induced a change from guaiacyl-syringyl lignin into a mainly guaiacyl lignin in the gum-occluded parts of the xylem. Considerable amounts of the phenolic amide dianthalexin and of other dianthramide phytoalexins were present in occluded xylem, but not in adjacent phloem, medulla or unoccluded xylem. Xylem from susceptible 'Lena' suffering degradation was characterized by a loss of syringyl groups from the lignin and by demethylation of pectin in an early stage of infection. Small quantities of dianthalexin and other dianthramide phytoalexins were found in 'Lena' when local defense responses (particularly occlusion) had occurred. In both cultivars evidence for degradation of hemicellulose was found.