Papel da hipoxia e do manganês na tolerância diferencial de clones de eucalipto à Seca de Ponteiro do Vale do Rio Doce

• Autor(a) principal: Lacerda, Fellip Januário Pinheiro
• Data de Publicação: 2013
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/5518
• topic: SPEVRD; Hipoxia; Manganês; SPEVRD; Hypoxia; Manganese; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO

The physiological disorder shoot die-back of eucalyptus in the Vale do Rio Doce (SPEVRD) is characterized by brownish necrotic lesions at the point of insertion of secondary branches and petioles, resulting in intense defoliation and, in the most extreme cases, in plant death. Close correlations of this problem were observed with hypoxic environments (low redox potential) and excess Mn in groundwater. This study aimed to investigate the mechanisms involved in the differential tolerance of eucalyptus clones to SPEVRD and their relationship to hypoxia and excess Mn. Three experiments were conducted for this purpose: Experiment I - treatments arranged in a factorial 2 x 2 x 5 design, represented by two clones (1213 - SPEVRD-sensitive and 2719 - SPEVRD-tolerant ); two O2 concentrations in solution (normal - 8 mg L-1 O2 and hypoxic - 1 mg L-1 O2); and five Mn concentrations (0, 5, 10, 30, and 90 mg L-1 MnCl2. 4H2O) . After the experiment, each plant was separated into old (mature) and new leaves, stem and roots, and oven-dried. These samples were ground and nitric/perchloric acid digested to determine Mn. Experiment II: The treatments consisted of a factorial 2 x 4 design, with: two clones - a sensitive (1213) and a tolerant (2719) and four O2 concentrations in nutrient solution (1, 4, 6, and 8 mg L-1 O2). The root and shoot length were measured 0 and 21 days after the beginning of the experiment. After 14 days, some physiological properties were evaluated: photosynthesis, stomatal conductance, transpiration, and internal CO2 concentration. Then, samples were taken from the root apex for anatomical analyses. At the end of the experiment, the plants were harvested and separated into old and new leaves, stems, and roots and oven-dried. Subsequently, the samples were digested to determine the macro and micronutrient levels. Experiment III: The treatments were arranged in a factorial 2 x 2 x 2 design, with two eucalyptus clones - 1213 (sensitive) and 2719 (tolerant), two O2 concentrations (normal - 8 mg L-1 and hypoxic - 6 mg L-1) and two Mn concentrations (30 and 300 mg L-1). The length of the root system was measured 0, 2, 5, 10, 15, 18 and 27 days after the beginning of the experiment. The gain in shoot height and throughout the experimental period was measured at the beginning and the end (27 days) of the experiment. At the end of the experiment, before harvest, the ethylene emitted by plants was quantified. Then, the seedlings were harvested and separated into old and young leaves, stems, and roots and oven-dried. We then determined the levels of macro and micronutrients. The hypoxic condition reduced the dry matter of the plant components, root growth and plant size. Most of these attributes were more affected in the sensitive clone 1213. Root growth was the best indicator of the stress caused by hypoxia; the growth of clone 1213 was most inhibited, while root growth inhibition was not influenced by Mn. The hypoxic condition caused the formation of aerenchyma in roots and increased ethylene in the shoots of both clones, mainly for the sensitive clone 1213. The tolerant clone 2719 responded faster to hypoxia than the sensitive clone (1213), reducing the stomatal opening and consequently the photosynthetic rate, transpiration and internal CO2 concentration to lower values than of the sensitive clone 1213. Under hypoxic conditions and excess Mn, the sensitive clone (1213) showed symptoms of Mn toxicity, e.g., brownish necrosis and shriveling of young leaves, followed by loss of apical dominance. The O2 deficiency in the root system is the first factor to predispose clones to SPEVRD, whereas Mn excess seems to have a long-term action until the eucalyptus die-back symptoms are fully expressed.