Resumo -Os objetivos deste trabalho foram determinar o controle genético da eficiência no uso do nitrogênio (EUN), identificar a importância das eficiências na absorção (EAN) e na utilização (EUtN) na sua composição, e quantificar relação entre produção de matéria seca da parte aérea (MPS) e do sistema radicular com a EUN e com seus componentes. Foram avaliadas 41 combinações híbridas em duas disponibilidades de N: baixa (BN) e alta (AN). Utilizou-se o delineamento de blocos ao acaso com duas repetições, em arranjo fatorial simples (combinação híbrida x disponibilidade de N). As análises estatísticas foram realizadas por meio das equações de modelos mistos. Correlações de elevada magnitude foram detectadas entre EAN e EUN, bem como entre essas eficiências e a MPS, tanto em BN como em AN. Em ambas as disponibilidades de N, efeitos genéticos aditivos apresentaram maior importância para os caracteres associados à EUN. Dessa forma, a seleção baseada no desempenho individual de linhagens quanto à MPS pode possibilitar a obtenção de genótipos com alta EUN. Independentemente da disponibilidade de N, a EAN é o componente mais importante da EUN.Termos para indexação: Zea mays, capacidade de combinação, disponibilidade de nitrogênio, estresse nutricional, REML/Blup, sistema radicular. Genetic effects of traits associated to nitrogen use efficiency in maizeAbstract -The objectives of this work were to determine the genetic control of nitrogen use efficiency (NUE), to identify the importance of N acquisition (NAE) and utilization (NUtE) efficiencies on its composition, and to quantify the relation between production of shoot (SDM) and root dry matter mass with NUE and its components. Forty-one hybrid combinations were evaluated in two N availabilities: low (LN) and high (HN). A randomized complete block design with two replicates, in a simple factorial arrangement (hybrid combination x N availability), was used. Statistical analyses were done using mixed model equations. High magnitude correlations were detected between NAE and NUE, and between these efficiencies and SDM in LN and HN. In both N availabilities, additive genetic effects were more important for the traits associated with NUE. Therefore, selection based on the individual performance of inbred lines as to SDM can allow for the obtainment of genotypes with high NUE. Independently of N availability, NAE is the most important component of NUE.

-Soybean plants with resistance to the stink bug complex are currently selected by extremely labor-intensive methods, which limit the evaluation of a large number of genotypes. Thus, this paper proposed the use of an alternative trait underlying the selection of resistant genotypes under field conditions with natural infestation: the weight of healthy seeds (WHS). To this end, 24 genotypes were evaluated under two management systems: with systematic chemical control of insects (management I), and without control (management II). Different indices were calculated using grain weight (Y P ) of management I and WHS of management II (Y S ). The high correlation between Y S and the indices mean productivity, stress tolerance and geometric mean productivity, plus the agreement in determining the groups of genotypes with resistance and high yield indicate that WHS is a useful character in simultaneous selection for these traits.

Stink bugs that affect soybeans are responsible for significant losses in seed production, quality and germination potential, in addition to hindering the mechanized harvest. To develop insect resistant materials, the breeder can compile a selection index by factor analysis. Therefore, the objective of this work was to validate the use of factor analysis, by means of its estimated gains, for the selection of highly productive and stink bugs resistant genotypes in two soybean segregating populations. For this, the phenotypic evaluation was performed in the generation F 2:3 , in two distinct experiments, being the populations from the crosses between IAC-100 × PI 295952 and IAC-100 × PI 306712. The experiments were installed in an 18 × 9 alpha-lattice design, with three replicates for each population. Agronomic and resistance characters were evaluated. The factorial scores for each character were obtained for the creation of "supercharacters". These were designed to check if the selection in the new characters could provide satisfactory simultaneous gains in the original characters. Subsequently, the analysis of variance was performed for all factors, in both populations. The F test showed the presence of variability among genotypes, allowing the selection of superior genotypes. None of the factors selected progenies with all the characters favorably, and their use was not interesting for both populations. With this, complementary studies should be performed with other selection indices in these populations.

Nitrogen (N) limitation in maize crops is related to the fact that the efficiency of nitrogen fertilization in maize does not exceed 50%, primarily due to volatilization, denitrification and soil leaching. Therefore, the development of new nitrogen use efficient (NUE) cultivars is necessary. The aim of the present study was to develop indices for the accurate selection of NUE maize genotypes for use in conditions of both high and low N availability. The experiment was conducted in a greenhouse (20°45'14"S; 42º52'53"W) at the Federal University of Viçosa during October 2010. A total of 39 experimental hybrid combinations and 14 maize lines differing in NUE were evaluated under two N availability conditions. We determined the relative importance of the studied characters using principal component analysis, factor analysis and by developing efficient selection indices. We conclude that indirect and early selection of tropical maize genotypes can be performed using the indices I HN = 0.022 SDM + 0. Key words: abiotic stress, NUE, maize improvement.Índices de seleção de genótipos de milho tropical para eficiência no uso de nitrogênio ResumoAs limitações do N no cultivo do milho relacionam-se ao fato de a eficiência da adubação nitrogenada no milho não ultrapassar os 50%, principalmente devido aos processos de perda por volatilização, desnitrificação ou lixiviação no solo. Nesse contexto, torna-se importante o desenvolvimento de cultivares eficientes no uso de N (EUN). Assim, o objetivo foi elaborar índices que permitissem a seleção acurada de genótipos de milho eficientes no uso de nitrogênio para as condições de alta e baixa disponibilidade desse nutriente. O experimento foi conduzido em casa de vegetação na Universidade Federal de Viçosa (20º45'14''S; 42º52'53''W) durante o mês de outubro de 2010. Foram avaliadas 39 combinações híbridas experimentais e 14 linhagens de milho divergentes para a eficiência no uso de N em duas condições de disponibilidade desse nutriente. Foram realizadas a análise de importância relativa dos caracteres estudados, estimada por meio do método dos componentes principais, a análise de fatores e a confecção dos índices de seleção. A seleção indireta e precoce para genótipos de milho tropical pode ser realizada por meio dos índices I AN = 0,022 MPS + 0,35 PASR + 0,35 CR AXI + 0,35 EUN, para ambientes de alta disponibilidade de nitrogênio, e I BN = -0,06 PSAR + 0,35 AS AXI + 0,35 CR AXI + 0,39 MPS, para condições de baixa disponibilidade de nitrogênio.Palavras-chave: estresse abiótico, EUN, melhoramento de milho.