Chitinase and peroxidase activities are induced in eucalyptus roots according to aggressiveness of Australian ectomycorrhizal strains of Pisolithus sp.

Peroxidase and chitinase activities were measured in roots of Eucalyptus globulus spp bicostata Kirkp. during colonization by Pisolithus sp. isolated from under Eucalyptus. Ten fungal isolates, ranging from poor to good root colonizers, were selected to represent a range of ectomycorrhizal aggressivity. The induction of chitinases and peroxidases was strongly related to the aggressiveness of the fungal strain. Only good colonizers, that is strains which rapidly form differentiated ectomycorrhizas, induced a strong response in the plant. Therefore, it can be concluded that these enzymes are not responsible for poor root colonization by the less aggressive strains. The chitinase response of Eucalyptus roots to contact with fungal extracts differed only slightly between weakly and strongly aggressive strains. This suggests that a major component of differential induction observed in vivo is the consequence of root colonization, tissue penetration and the ability to deliver elicitors to the plain print to and during rant colonization.