Changes in Water Relations Associated With Infection by Phytophthora cinnamomi

Changes in water relations associated with infection by Phytophthora cinnamomi were measured for three native species from the Brisbane Ranges forest. Measurements included leaf conductance, stomatal aperture, transpiration, water potential and relative water content in container-grown plants of Isopogon ceratophyllus (highly susceptible), Eucalyptus macrorhyncha (field-susceptible) and E. goniocalyx (field-resistant) maintained in a glasshouse. I. Ceratophyllus showed a large and highly significant difference in water relations between infected and control plants. Infection was associated with stomatal closure, reduced transpiration, reduced relative water content and leaf water potential. These reactions to infection were not observed for either of the glasshouse-reared Eucalyptus species. In the forest diseased E. macrorhyncha showed significant differences in leaf conductance compared with healthy trees, whereas E. goniocalyx forest trees showed less infection-associated variation. This variation in leaf conductance was not associated with water stress.