Changes in Mineral Content of Eucalyptus marginata and E. calophylla Grown under Controlled Conditions and Inoculated with Phytophthora cinnamomi

Mineral concentrations in infected roots and shoots were compared with similar material, but pathogen free, for the susceptible Eucalyptus marginata and the field resistant E. calophylla. All plants were mycorrhiza-free, grown under controlled conditions and inoculated with an axenic suspension of zoospores of Phytophthora cinnamomi. Plant material was ashed 30 days after inoculation and analyzed in an external proton beam using PIXE and nuclear reaction analyis to detect differences in mineral concentrations. The mineral content of infected roots of E. marginata was below that of the uninfected roots for all elements detected except chlorine, chromium and rubidium. The reductions were significant for calcium and copper. No such reduction was found, in E. calophylla roots, but some changes were detected. Shoot: root ratios of E. marginata showed significant differences associated with infection in phosphorus, calcium, copper and zinc. Relatively large differences were also recorded for sulphur chlorine and potassium. Shoot: root ratios of infected E. calophylla showed fewer differences but contained only half the concentrations of sulphur and potassium present in the controls. The reduced mineral concentrations reflect the failure in conduction of water and minerals through the infected and susceptible root system.