Abstract
An aeroponics root chamber has been designed for evaluating the influence of low oxygen on disease resistance in clonal Eucalyptus marginata infected with Phytophthora cinnamomi. Actively growing clones of E. marginata were transferred into the aeroponics chamber and liquid feed is delivered in a fine spray, providing optimal conditions for root growth. Prior to infection by zoospores of P. cinnamomi under normal oxygen, roots were exposed to 4 treatments; (i) normal oxygen, 8 mg 02 L -I, (ii) 6 days of hypoxia, 2 mg 02 L-1, (iii) 6 hrs of anoxia, >0.05 mg 02 L-1, and (iv) 6 days of hypoxia, followed by 6 hrs of anoxia. Root extension during hypoxia was greatly reduced. The anoxic treatments resulted in the death of the apical meristem. Infection development (lesion extension) was least for the hypoxic pre-treated roots and greatest for roots placed directly under anoxia. This is possibly related to an accumulation of soluble sugars in the roots during hypoxia.