Response of Eucalyptus marginata (Jarrah) to simulated waterlogging and Phytophthora cinnamomi infection

This study examined the effect of simulated temporary waterlogging the interaction between E. marginata and P, cinnamomi. An aeroponic chamber has been designed which allows the roots of 7 month old clonal plants or seedlings to be subjected to a range of oxygen concentrations. Roots grown under normal oxygen were compared with those that had been exposed to either 6 days of hypoxia (2 mg O-2 l(-1)) or 6 hr. of anoxia (< 0.05 mg O-2 l(-1)) prior to infection by zoospores of P. cinnamomi. The roots were inoculated with a 5 mu l suspension of zoospores and harvested after 2 days. Pre-treatment with an anoxic shock resulted in more rapid lesion extension, and an hypoxic treatment of 6 days in less rapid lesion extension, than seen in clones grown under normal oxygen conditions. The reduced susceptibility of hypoxic treated roots and the increased susceptibility of anoxic treated roots could not be explained by either defense enzyme accumulation or soluble carbohydrate accumulation. Studies are now focusing on other changes in metabolism associated with hypoxia that may explain these differences.