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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 O2 concentrations (normal and hypoxic) and five concentrations of Mn (0, 5, to 90 mg L-1); (II) same two eucalyptus clones, two O2 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 O2 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.

The use of a commercial bleach solution (CB) for in vitro propagation of orchids has proven to be an efficient technique and an alternative to the use of the autoclave and laminar flow chamber (LFC). The aim of this study was to evaluate the use of CB in disinfestation of culture media (CM) for seeding and for re-cultivation of orchid plantlets and its effect in different types of flasks and on the nutritional state of the plantlets. In the seeding experiment , seeds of Laelia tenebrosa Rolfe were used, with evaluation of three types of flasks; five concentrations of CB applied to the CM of 2, 5, 10, 20 and 40 mL L -1 and the control treatment. In the re-cultivation experiment , Cattleya kerri Brieger & Bicalho plantlets were used. The rates of CB added to the CM were 2, 5, 10, 20, 30, 35 and 38 mL L -1 in polypropylene containers, and the rates sprayed on the plantlets at re-cultivation were 5, 12.5, 25, 50, 75, 87.5 and 95 mL L -1 . The proportion of germinated seeds and the dry matter weight of the protocorms were greater in the control treatment. The increasing rates of CB added to the CM had worse results for germination in glass flasks. In re-cultivation, there was no significant difference in the growth of the plantlets between the autoclaved flasks and those disinfested in CB. Keymessage: Both orchid seeding and re-cultivation of seedlings can be carried out entirely and efficiently without the use of an autoclave and laminar flow chamber, using chemical disinfection with commercial bleach.