LAUSR

Eucalyptus shoot blight in the Rio Doce Valley (ESBVRD) is a physiological anomaly that has been related to hypoxic environment and Mn excess. This study had the objective of understanding the mechanisms involved in the differential tolerance of eucalyptus clones to ESBVRD. Two experiments were carried out: (I) two clones, a sensitive and a ESBVRD tolerant, two O 2 concentrations (normal and hypoxic) and five concentrations of Mn (0, 5, to 90 mg L -1 ); (II) same two eucalyptus clones, two O 2 concentrations (normal and mild hypoxic) and two Mn concentrations (30 and 300 mg L -1 ). The hypoxic condition reduced the plant dry weight and increased the production of ethylene in the two clones, both more strikingly in the sensitive clone. The O 2 deficiency was the first factor predisposing the clones to ESBVRD, in contrast to Mn excess, that appeared to act over a longer period for the expression of the symptoms.