Identifying maize inbred lines that are more efficient in nitrogen (N) use is an important strategy and a necessity in the context of environmental and economic impacts attributed to the excessive N fertilization. N-uptake efficiency (NUpE) and N-utilization efficiency (NUtE) are components of N-use efficiency (NUE). Despite the most maize breeding data have a multi-trait structure, they are often analyzed under a single-trait framework. We aimed to estimate the genetic parameters for NUpE and NUtE in contrasting N levels, in order to identify superior maize inbred lines, and to propose a Bayesian multi-trait multi-environment (MTME) model. Sixty-four tropical maize inbred lines were evaluated in two experiments: at high (HN) and low N (LN) levels. The MTME model was compared to single-trait multi-environment (STME) models. Based on deviance information criteria (DIC), both multi- and single-trait models revealed genotypes x environments (G x E) interaction. In the MTME model, NUpE was found to be weakly heritable with posterior modes of heritability of 0.016 and 0.023 under HN and LN, respectively. NUtE at HN was found to be highly heritable (0.490), whereas under LN condition it was moderately heritable (0.215). We adopted the MTME model, since combined analysis often presents more accurate breeding values than single models. Superior inbred lines for NUpE and NUtE were identified and this information can be used to plan crosses to obtain maize hybrids that have superior nitrogen use efficiency.

-The objectives of this work were to study the genetic control of grain yield (GY) and nitrogen (N) use efficiency (NUE, grain yield/N applied) and its primary components, N uptake efficiency (NUpE, N uptake/N applied) and N utilization efficiency (NUtE, grain yield/N uptake), in maize grown in environments with high and low N availability. Experiments with 31 maize genotypes (28 hybrid crosses and three controls) were carried out in soils with high and low N rates, in the southeast of the state of Minas Gerais, Brazil. There was a reduction of 23.2% in average GY for maize grown in soil with low N, in comparison to that obtained with high N. There were 26.5, 199 and 400% increases in NUtE, NUpE, and NUE, respectively, for maize grown with low N. The general combining ability (GCA) and specific combining ability (SCA) were significant for GY, NUE and NUpE for maize grown in high N soil. Only GCA was significant for NUpE for maize grown in low N soil. The GCA and SCA for NUtE were not significant in either environment. Additive and non-additive genetic effects are responsible for the genetic control of NUE and GY for maize grown in soils with high N availability, although additive effects are more important. Index terms: Zea mays, abiotic stress, absorption efficiency, combining ability, commercial hybrids, utilization efficiency. Controle genético da produção de grão e da eficiência de uso do nitrogênio em milho tropicalResumo -O objetivo deste trabalho foi estudar o controle genético da produtividade de grãos (PG) e da eficiência no uso de nitrogênio (EUN, produção de grãos/N aplicado) e seus componentes primários -eficiência de absorção (EAbN, N absorvido/N aplicado) e utilização (EUtN, produção de grãos/N absorvido) -, em milho cultivado em ambientes com alta e baixa disponibilidade de nitrogênio. Trinta e um genótipos de milho (28 cruzamentos entre híbridos comerciais e três testemunhas) foram avaliados em solos com alta e baixa doses de aplicação de N. Houve redução de 23,2% na média de PG em milho cultivado em solo com baixo teor de N, em relação à obtida com alto N.

The aim of this study was to evaluate the adaptability and stability of 29 commercial maize hybrids in the southeast of the State of Minas Gerais, Brazil, employing three methods. The 29 commercial maize hybrids from the 2014/2015 crop were evaluated for grain yield in five locations in the southeast of Minas Gerais. A randomised-block design was used, with two replications. Each lot comprised two rows, five meters in length, at a spacing of 0.80 m, giving an effective area of 8.00 m2. In addition to individual and combined variance analysis, the methods of Eberhart & Russell (1966), AMMI (Additive Main Effects and Multiplicative Interaction Analysis) and mixed models were used to evaluate the adaptability and stability of the 29 hybrids. There was a significant difference (P<0.01) for the effects of hybrid, environment and the hybrid x environment interaction. The majority of the hybrids under evaluation displayed broad adaptability with good stability. It was concluded that the Eberhart & Russell, AMMI and mixed-model methods show similar results in classifying maize hybrids of broad adaptability. There is a difference in indicating hybrids with specific adaptability to favourable and unfavourable environments. Based on the three methods, the hybrids SHS7920PRO, BM709PRO2, BRS1055 and BM650PRO2 show a general adaptability for the environments under evaluation.

Resumo -O objetivo deste trabalho foi identificar os efeitos genéticos que controlam a herança de caracteres associados à eficiência de utilização do fósforo (EUP) em milho e determinar as relações entre esses caracteres. Foi realizado um dialelo entre seis cultivares de milho do qual foram obtidas 15 combinações híbridas. Estas cultivares foram avaliadas em alta e baixa disponibilidade de fósforo, em casa de vegetação e campo. Foram medidas a resposta das plantas à disponibilidade de fósforo (RU) e as características associadas às eficiências de utilização e translocação do nutriente. As combinações híbridas apresentaram interação significativa com a disponibilidade de P, para os caracteres massa de matéria seca da planta (MSP), teor de P na planta (PAP) e razão entre as massas de matéria seca da parte aérea e da raiz (RMS). A interação entre capacidade geral de combinação e RU foi significativa para PAP e RMS e, entre capacidade específica de combinação e RU, para MSP e PAP. As EUP em baixa e alta disponibilidade do nutriente estiveram correlacionadas entre si e com RU. A EUP em baixa disponibilidade de P não se correlacionou com a produtividade de grãos. Contudo, sob alta disponibilidade do nutriente, esses parâmetros se correlacionaram. Os efeitos não aditivos têm maior importância para caracteres relacionados à EUP, de modo que a seleção deve ser realizada nas combinações híbridas.Termos para indexação: Zea mays, capacidade de combinação, estresse abiótico, melhoramento vegetal, nutrição mineral. Inheritance of traits associated with phosphorus utilization efficiency in maizeAbstract -The objective of this work was to determine the genetic effects that control the inheritance of characters associated with the phosphorus utilization efficiency (PUE) in maize, and to determine the relationship among them. A diallel between six maize cultivars was performed and 15 hybrid combinations were obtained from it. These cultivars were evaluated in high and low phosphorus availability in the greenhouse and field. Plant response to nutrient availability (RU) and traits associated to utilization and translocation efficiency were measured. There were significant interactions between hybrid combinations and phosphorus availability for plant dry matter mass (MSP), P concentration in plants (PAP), and the ratio between shoot and root dry matter masses (RMS). The interaction between general combining ability and P availability was significant for RMS and PAP, and the one between specific combining ability and P availability, for MSP and PAP. The PUE in low and high P were correlated with each other and with RU. The PUE at low P availability was not correlated to grain yield. However, in high soil P availability these parameters were correlated. Non additive effects are more important for traits related to PUE, so that selection should be carried out on hybrid combinations.

Reciprocal recurrent selection (RRS) has been successfully applied to maize breeding for more than 60 years. Our objective was to assess the relative efficiency of the genotypic value and the effects of general and specific combining abilities (GCA and SCA) on selection. The GCA effect reflects the number of favorable genes in the parent. The SCA effect primarily reflects the differences in the gene frequencies between the parents. We simulated three traits, three classes of populations, and 10 cycles of half- and full-sib RRS. The RRS is a highly efficient process for intra- and interpopulation breeding, regardless of the trait or the level of divergence among the populations. The RRS increases the heterosis of the interpopulation cross when there is dominance, and it decreases the inbreeding depression in the populations and the genetic variability in the populations and in the hybrid. When there is not dominance and the populations are not divergent, the RRS also determines population differentiation. The half-sib RRS, which is equivalent to selection based on the GCA effect, is more efficient than the full-sib RRS based on the genotypic value, regardless of the trait or the level of improvement of the populations. The full-sib RRS based on the SCA effect is not efficient for intra- and interpopulation breeding.