Eficiência de uso de nitrogênio e atividade da nitrato redutase e glutamina sintetase em milho

• Autor(a) principal: Oliveira, Lucimar Rodrigues de
• Data de Publicação: 2009
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1127
• topic: Zea mays; Melhoramento; Estresse abiótico; Seleção; Nitrogênio; Zea mays; Improvement; Abiotic stress; Selection; Nitrogen; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOTECNIA

This work aims to evaluate strategies to increase the nitrogen use efficiency, as the amount of dry matter produced per nitrogen unit and the enzymes activities of reductase nitrate and synthetase glutamine in the early corn plants selection. Three experiments were installed in a greenhouse in pots filled with sand and two treatments of nitrogen (N), maintained in Hoagland solution. In experiment 1, 10 corn strains were evaluated without prior informing about N use efficiency at two N treatments (2 mM and 0.2 mM). In experiment 2, eight corn strains were selected with contrasting performances on the absorption and N utilization in two N treatments (10 mM and 1 mM). In experiment 3, twenty-two hybrids and three witnesses in two N treatments (10 mM and 1 mM) were evaluated. In all greenhouse experiments, the plants were harvested at the four fully quite leaves stage. For experiment 1, the characteristics of air-dry matter (ADM), root dry matter (RDM), total dry matter (TDM), nitrogen use efficiency (NUE) and glutamine synthetase activity (GS) showed significant differences at high and low N doses. The nitrogen absorption efficiency (NAE) was significant at high-N dosis, and nitrate reductase (NR) was significant at low N dosis. The correlations among NR enzymes activity and GS and the other defining features were low; negative for high N; low and positive for low N. For N use efficiency (NUE), high and significant correlations were observed with ADM, RDM, TDM, and NUE characteristics at high and low N. For the experiment 2, NUE and NAE showed significant differences at high N. NAE, NUtE, NUE, and NR and GS enzymes activities showed significant differences at low N. For experiment 3, the significant features in high N were ADM, ADM/RDM relationship, and NAE; at low N were ADM, RDM, TDM, and NUE. Two field experiments to evaluate twenty-two-hybrid and three witnesses in two nitrogen doses, 120 and 30 kg ha-1, were also installed, classified as high and low N, respectively. At high N, the grains productivity (GP) characteristics, NUE, NUtE, and NAE showed significant differences. At low N, none of the characteristics showed significant difference. The NR enzymes activities and GS were not efficient to discriminate corn hybrids in the field. In experiment 1, at high N, only GS was efficient in the strains discrimination and it is associated with NUE; in low N, the NR and GS enzymes activities were efficient and are associated with NUE. In experiment 2, in high N, only NAE was efficient in the strains discrimination. The NR enzyme and GS activity, NUE and NAE were efficient to discriminate the strains to NUE at low N. In experiment 3, at high N, the highest NUE are associated to NAE and to at least one of NR and GS enzymes with higher activity. At low N, NUE is associated with greater absorption, with nutrient use, with reduced NR activity, and with higher GS activity. In field experiments, the hybrids showed high genetic variability in high N; at least one of the efficiencies, NUtE or NAE is related to higher NUE at high and low N; the lowest NR activity or the highest GS activity is related to NUE. It follows that the strains and hybrids selection with higher nitrogen use efficiency can not be done based only on the nitrate reductase and glutamine synthetase activity; the nitrate reductase and glutamine synthetase activity is related to nitrogen use efficiency; the selection criteria to identify genotypes with greater nitrogen use efficiency vary according to nutrient availability.