Biochemical interactions of conifer seedling roots with Fusarium spp.

The importance of root and spore surface molecules in the interactions of F usarium spp. with conifer roots, and cellular localization of proteins pres umed to be involved in host defence, were investigated. For adhesion studie s, using a combination of fluorescein isothiocyanate (FITC) labelled lectin s and high perfomance liquid chromatography (HPLC), several sugars (pinitol , xylitol, galactose, mannose, and glucose) were detected in root surface m ucilage. Both artificial substrata and detached living roots were used to e valuate the significance of selective removal of root or spore surface comp onents on the adhesion process. The spores or roots were pretreated with ei ther periodic acid, pronase E, potassium hydroxide or diethyl ether. Pretre atment of the spores with diethyl ether reduced significantly the level of spore adhesion, which suggests that the adhesive component is either a lipi d, or is bound to lipid. Since oxidation of carbohydrate reactive sites wit h periodic acid on the root surface almost completely abolished the develop ment of germ tubes by adherent spores, it was presumed that some of these p eriodate-sensitive substances serve as a nutrient source for the fungus. On inoculated roots, F. avenaceum and F. culmorum were significantly pathogen ic to both Norway spruce and Scots pine seedlings. Cytochemical labelling o f sites of accumulation of host defence molecules within infected root tiss ues using anti-peroxidase demonstrated increased peroxidase activity in hos t cell walls. With anti-chitinase and anti-glucanase, gold labelling was fo und mainly on pathogen hyphal walls.