Differential response of four carnation cultivars to races 1 and 2 of fusarium oxysporum f.sp. dianthi and to Phialophora cinerescens

The responses of four carnation cultivars to infection with races 1 or 2 of Fusarium oxysporum f.sp. dianthi and with Phialophora cinerescens were investigated. Four and nine days after stem inoculation with the different wilt pathogens, 5 cm stem segments were extracted and analysed for the accumulation of dianthalexins and dianthramides by HPLC, and approximately 1 mm³ blocks of xylem tissue were sampled and analysed by pyrolysis-mass spectrometry. Analysis of wilt development over a two-month period confirmed the differential responses of the cultivars to the pathogen isolates. The level of accumulation of the dianthramides was determined partly by the cultivar and partly by the invading pathogen and was not related to the level of symptoms developed. P. cinerescens induced the highest dianthramide concentrations, followed by F. oxysporum f.sp. dianthi, race 2. Race 1 elicited slight dianthramide accumulation and was less inhibited by them in vitro than was P. cinerescens. Pyrolysis-mass spectrometry indicated lignin degradation by all fungi and confirmed, in increasing order, induction of dianthramide phytoalexin accumulation in plants infected with F. oxysporum f.sp. dianthi race 1, race 2 and P. cinerescens. Irrespective of the pathogen, each inoculated cultivar showed a unique pattern of demethylation and degradation of pectin, degradation of lignin and hemicellulose, and changes in polysaccharide-bound phenolic acids.