INFLUENCE OF LOW-OXYGEN LEVELS IN AEROPONICS CHAMBERS ON EUCALYPT ROOTS INFECTED WITH PHYTOPHTHORA-CINNAMOMI

Aeroponics root chambers were designed to evaluate the influence of lo w oxygen on disease development in clones of Eucalyptus marginata susc eptible or resistant to infection by Phytophthora cinnamomi. Actively growing 7-month-old clones of E. marginata were transferred into the a eroponics chambers, into which a nutrient solution was delivered in a fine spray, providing optimal conditions for root growth. Prior to ino culation by zoospores of P. cinnamomi under normal oxygen, the roots w ere exposed to four treatments: (i) normal oxygen, approximately 8 mg of O-2 liter(-1); (ii) 6 days of hypoxia, 2 mg of O-2 liter(-1); (iii) anoxic acclimatization 2 days at 2 mg of O-2 liter(-1), 2 days at 1 m g of O-2 liter(-1), 2 days at 0.5 mg of O-2 liter(-1), 2 days at 2 mg of O-2 liter(-1), and 6 h at <0.05 mg of O-2 liter(-1); and (iv) 6 h o f anoxia, <0.05 mg of O-2 liter(-1). Root extension during hypoxia was greatly reduced, Lesion development was least for roots exposed to hy poxia and greatest for roots exposed to anoxia for 6 h, suggesting inc reased resistance of E. marginata to P. cinnamomi following hypoxia.