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 rnotsi of Eucalyptus ghhulus spp. bicustata {Wdid. et aL) 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 aggrfssi\'ity. 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 tu contact with fungal extracrs differed only siightly between weakly and strongly aggressive strains. Thi.s suggests that a major component of ditferential induction observed in I'ivo is the consequence of root colonization, tissue penetration and tht ability to deliver elicitors to the plant prior to and during root colonization.