Brazil is an agricultural country, with 190 Mha of pastures sustaining 209 million cattle. Fewer than 10% of the cattle are fattened in feedlots, whereas cattle reared on pastures have a competitive advantage for export, eliminating the risks presented by the mad cow disease (bovine spongiform encephalopathy) and considerations related to animal welfare. Brazil has been the world’s largest exporter of beef since 2004 and has the largest commercial herd in the world. In 2011, 16.5% of its production was exported, and the livestock sector contributed 30.4% of the gross national product from agribusiness and 6.73% of the total GNP. Many forage breeding programs, mainly at Embrapa, have contributed to the development of improved pastures, and cultivars of Brachiaria brizantha, B. decumbens, B. humidicola and Panicum maximum are the main pastures used in the country. All have apomictic reproduction, which means there are few cultivars occupying very large, continuous areas, thus suggesting a risk to the productive system. Such is the case of B. brizantha cv. Marandu, which occupies around 50 Mha. The Brazilian tropical forage seed industry is also important, and Brazil is the main seed exporter, supplying all Latin American countries. Due to pasture degradation, around 8 Mha is renovated or recovered each year. Forages are also used and planted each year in integrated crop–livestock and integrated crop–livestock–forest systems. Nowadays, these systems occupy 4 Mha. Improved pastures are thus a major asset in Brazil not only for the beef production chain but also for the dairy industry.

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A seleção de caracteres relacionados à tolerância à deficiência hídrica em milho tem sido objeto de interesse em programas de melhoramento, principalmente em virtude da ineficiência da seleção para produzir grãos nessas condições. O objetivo deste trabalho foi estimar parâmetros genéticos em duas populações de milho tropical. Foram avaliadas duas populações (denominadas D e U) com 256 progênies F 2:3 , no delineamento em látice 16 x 16 em sete ou nove ambientes e densidade populacional de 62.500 plantas ha -1 . Diferenças significativas foram constatadas entre progênies (P), ambientes (A) e para a interação P x A em ambas as populações. Os coeficientes de herdabilidade em nível de médias de progênies variaram entre 73,52% para prolificidade na população D e 95,88% para florescimento feminino (FF) na população U. No caráter produção de grãos (PG) houve correlação genética significativa nas populações U e D, respectivamente, com prolificidade (0,79 e 0,88) e florescimento feminino (-0,76 e -0,44); na população U com florescimento masculino (-0,74) e; na população D com stay-green (-0,50). Não foi constatada correlação genética significativa entre PG e intervalo entre florescimentos (IF). Os parâmetros genéticos estimados sugerem que a utilização de índices de seleção que incluam, além de PG, caracteres como prolificidade, FF e SG na seleção de progênies sob condições normais de umidade, poderia propiciar o desenvolvimento de material com alta produtividade e boa tolerância a estresses hídricos.Palavras-chave: Estresse hídrico, estresse abiótico, correlação, produção de grãos, stay-green. ABSTRACT GENETIC PARAMETERS OF DROUGHT TOLERANCE RELATED TRAITS IN TROPICAL MAIZEThe selection of drought tolerance related traits in maize has been object of interest in improvement programs, mainly in function of the selection inefficiency for grain yield on these conditions. The objective of this work was to estimate genetic parameters in two populations of tropical maize. Two populations (called D and U) with 256 F 2:3 progenies had been evaluated in a 16x16 simple lattice, in seven and nine environments with population density of 62,500 plants ha -1 . Significant differences were observed among line (P), environments (A) and for the P x A interaction in both populations. The heritability coefficients at progenies level average had varied between 73.52% for prolificacy in population D and 95.88% for female flowering (FF) in population U. Grain yield (PG) presented significant genetic correlation in populations U and D, respectively, with prolificacy (0,79 and 0.88) and female flowering (-0,76 and -0,44); in population U with male flowering (-0.74) and; in population D with stay-green (-0.50). No genetic correlation was observed between PG and anthesis-silking interval (IF). Estimated of genetic parameters suggest that the use of selection indices that include, besides PG, characters as prolificacy, FF and SG in the selection process under conditions of normal water supply, could lead to the development of cultivars with high ...

A tropical forage breeding program contains several peculiarities, especially when it involves polyploid species and facultative apomixis. Urochloa spp. are excellent perennial forages, and the identification of superior genotypes depends on the selection of many characteristics under complex genetic control, with high cost and time‐consuming evaluation. Therefore, the use of tools such as multivariate analysis and diallel analyses could contribute to improving the efficiency of breeding programs. Thus, the objectives were to estimate (i) the contribution of additive and nonadditive effects on agronomical and nutritional traits in a population of interspecific hybrids of Urochloa spp., originated from a partial diallel between five apomictic and four sexual parents, and (ii) the accuracy of multivariate index selection efficiency. Genetic variability was detected between the parents, crosses, and hybrids for all the traits. There was no clear trend of the importance of the additive and nonadditive genetic effects on agronomical and nutritional traits. Furthermore, the predominant component of genetic variance changed depending on the characteristic. Moreover, there was no parent or cross that was outstanding for all traits simultaneously, showing the high variability generated from these crosses. The Mulamba and Mock index associated with principal components analysis allowed a more significant gain only for agronomic characteristics. However, the per se index, at the univariate level, promoted a more balanced response to selection for all traits.

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Year 1: full-sib progeny production. Year 2: progeny evaluation and selection. Year 3: recombination of selected sexual progeny, involving the sexual plants that gave rise to the selected progeny.

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Resumo -O objetivo deste trabalho foi estudar a herança da senescência retardada em milho. Foram realizados cruzamentos dialélicos parciais entre 50 linhagens e cinco testadores. Os 250 cruzamentos resultantes, além de seis híbridos comerciais utilizados como testemunhas, foram avaliados em oito ambientes, no delineamento látice simples 16x16, com duas repetições por ambiente. Os cruzamentos dialélicos foram analisados utilizando o método 4 do modelo 1 de Griffing, adaptado para múltiplos ambientes. A contribuição da capacidade geral de combinação (CGC) para a expressão do caráter "stay-green" (69,06%) foi maior que a da capacidade específica de combinação (CEC) (30,94%), evidenciando que os efeitos aditivos são mais importantes que os efeitos não aditivos na expressão deste caráter. Tanto a CGC como a CEC interagiram significativamente com o ambiente, indicando que a seleção para este caráter deve ser realizada com base nas médias de experimentos em diversos ambientes.Termos para indexação: Zea mays, CEC, CGC, cruzamento dialélico, stay-green. Inheritance of the delayed senescence in maizeAbstract -The objective of this research was to study the inheritance of delayed senescence in maize. Partial diallel crosses among 50 inbred lines and five testers were made. The 250 crosses, along with six commercial hybrids used as checks, were evaluated at eight environments in lattices 16x16 with two replications per environment. The diallel crosses were analyzed following the method 4 model 1 of Griffing, extended to multiple environments. The contribution of the general combining ability (CGA) for the expression of the stay-green trait (69.06%) was greater than the specific combining ability (SCA) (30.94%), showing that additive effects are more important than non-additive effects for the expression of this trait. Both GCA and SCA interacted significantly with the environments, indicating that the selection for this trait should be based on the means across environments.Index terms: Zea mays, SCA, GCA, diallel crossing, stay-green.Introdução relatam que o milho cultivado na maioria das regiões tropicais sofre uma redução de até 50% na produção devido ao estresse provocado por secas. De acordo com esses autores, o melhoramento genético pode reduzir de 15 a 25% essas perdas. Chapman & Edmeades (1999), a partir de resultados obtidos em um estudo para tolerância à seca, realizado com milho, sugerem que os genótipos com elevada senescência retardada ("stay-green"), alta prolificidade e reduzido intervalo entre florescimentos são menos afetados por estresses hídricos.Em programas de melhoramento genético de cereais, os genótipos são considerados "stay-green" quando as folhas e colmos permanecem verdes após o enchimento dos grãos. Dessa forma, após o enchimento dos grãos, a fotossíntese se prolonga fornecendo carboidratos para colmos, folhas e raízes e, conseqüentemente, as plantas apresentam maior resistência a estresses bióticos e abióticos (Tollenar & Wu, 1999;Jiang et al., 2004;Carmo et al., 2007). Além disso, os genótipo...