Chitinase activities are induced in Eucalyptus globulus roots by ectomycorrhizal or pathogenic fungi, during early colonization

A comparative study of root chitinase activities induced by the ectomycorrhizal basidimycete Pisolithus tinctorius Coker and Couch and the pathogenic fungus Phytophthora cinnamomi , has been carried out. Two chitinases were constitutively present in Eucalyptus globulus ssp. bicostata (Maid et al.) Kirkp. roots. When 7-day-old seedlings were challenged with the ectomycorrhizal fungus, root chitinase activity was stimulated already after 6 h, during the very early stages of ectomycorrhizal colonization. Comparing chitinase electrophoretic patterns induced by symbiotic strains more or less compatible with Eucalyptus , a strong stimulation of chitinase activity indicated a successful interaction, which evolved quickly towards root infection and mature mycorrhizae formation. Root chitinase activity remained constant over 7 days during the establishment of the symbiosis. No new chitinase band was induced by the pathogen, when compared with the symbiotic fungi. Chitinase activity was only stimulated quantitatively after pathogenic infection. Root chitinase activities were also stimulated by fungal cell extracts applied in vitro. Such stimulation mimicked precisely the stimulation by living fungi. The intensity of the plant response to fungal extracts was related to fungal strain aggressiveness.