Abstract
Summer rainfall seldom occurs in the south-west of Western Australia. Flora of the region has evolved under a Mediterranean climate having hot dry summers with rare thunder storms, and cool wet winters. The consequence of high summer rainfall is significant because the resulting conditions can favour an outbreak of the introduced soil pathogen, Phytophthora cinnamomi, to which many plant species in the south-west forests are susceptible.
A glasshouse experiment compared the response of drought stressed and non-stressed Eucalyptus marginata (jarrah) plants when inoculated with P. cinnamomi after a simulated summer rainfall event. Clonal plants, resistant or susceptible to P. cinnamomi, were tested. The moisture content of the container substrate for inoculated and non-inoculated plants was either kept at container capacity or at a pre-determined level just above that of the wilting point of each plant for 3 weeks. Sudden restoration to container capacity simulated summer rainfall and plants were inoculated immediately. Higher proportions of non-stressed clonal plants, both resistant and susceptible, became infected and were more extensively colonized by the pathogen than plants subjected to drought Results supported our hypothesis : tissue of drought affected E. marginata plants is less susceptible to infection by P. cinnamomi than tissue of plants which have recently experienced no water deficit.