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.

-Brazil has the largest commercial beef

RESUMO -O trabalho foi realizado com o objetivo de avaliar a produção de B. decumbens cv. Basilisk e B. brizantha,cultivares Marandu e Xaraés, sob diferentes níveis de sombreamento. Utilizou-se delineamento em blocos casualizados com esquema de parcelas subdivididas, considerando os níveis de sombreamento (0, 50, 70%) como parcela e as espécies ou cultivares como subparcelas. Sementes das gramíneas foram postas a germinar em bandejas e transplantadas (três plântulas por vaso).Foram realizados quatro cortes em cada subparcela. Antes de cada corte, mediram-se a altura de planta e a área foliar de quatro folhas em cada planta e quantificou-se o número de perfilhos vivos por vaso. Após a colheita, as plantas foram separadas em lâmina, colmo + bainha e material morto para determinação da produção de matéria seca. Para produção de matéria seca total, calcularam-se a produção média em cada um os cortes e a produção total. No último corte, avaliou-se a massa seca de raízes. As interações significativas foram desdobradas adequadamente. O fator qualitativo foi submetido à comparação de médias pelo teste Tukey e o quantitativo à análise de regressão linear. À exceção da produção média em quatro cortes e da produção de colmos e de material morto, observou-se interação significativa para todas as outras variáveis. Independentemente do nível de sombreamento, o cultivar Xaraés destacou-se positivamente na maioria das características analisadas, enquanto, no nível de 50% de sombreamento, o capim-braquiária apresentou maior produtividade, em porcentagem de produção a pleno sol. Na avaliação da porcentagem de folhas, destacou-se o capim-xaraés, seguido do capim-marandu. Independentemente da forrageira, o nível de sombreamento teve efeito direto sobre o número de perfilhos/planta, a produção de MS do sistema radicular, a área foliar e o valor SPAD.Palavras-chave: capim-braquiária, capim-marandu, capim-xaraés, silvipastoril Genus Brachiaria grass yields under different shade levels ABSTRACT -Yields of B. decumbens cultivar Basilisk and B. brizantha cultivars Marandu and Xaraés were evaluated under different shade levels. A completely randomized block split plot design was used, with the shade levels as plots (0, 50, 70%), and the species and cultivars as split-plots. Seeds were germinated on trays and three seedlings were transplanted to each pot. Four harvests were made on each split-plot. Prior to each harvest, plant height, number of live tiller per pot and the leaf area of four leaves per pot were recorded. After harvesting, the plants were separated into leaves, stem + sheaths and dead matter to determine dry matter yield. Total dry matter yield was calculated for each harvest and for the sum of harvests. In the last harvest, root dry matter yield was also evaluated. Significant interactions were unfolded adequately. The means of the qualitative factor (forages) were compared by the Tukey test and the quantitative factor (shade level) was submitted to linear regression analysis. With the exception of the mean yield in four har...

important for breeding programs that considerably influence animal productivity as well as the quality of meat and milk.

Genomic selection is an efficient approach to get shorter breeding cycles in recurrent selection programs and greater genetic gains with selection of superior individuals. Despite advances in genotyping techniques, genetic studies for polyploid species have been limited to a rough approximation of studies in diploid species. The major challenge is to distinguish the different types of heterozygotes present in polyploid populations. In this work, we evaluated different genomic prediction models applied to a recurrent selection population of 530 genotypes of Panicum maximum , an autotetraploid forage grass. We also investigated the effect of the allele dosage in the prediction, i.e. , considering tetraploid (GS-TD) or diploid (GS-DD) allele dosage. A longitudinal linear mixed model was fitted for each one of the six phenotypic traits, considering different covariance matrices for genetic and residual effects. A total of 41,424 genotyping-by-sequencing markers were obtained using 96-plex and Pst 1 restriction enzyme, and quantitative genotype calling was performed. Six predictive models were generalized to tetraploid species and predictive ability was estimated by a replicated fivefold cross-validation process. GS-TD and GS-DD models were performed considering 1,223 informative markers. Overall, GS-TD data yielded higher predictive abilities than with GS-DD data. However, different predictive models had similar predictive ability performance. In this work, we provide bioinformatic and modeling guidelines to consider tetraploid dosage and observed that genomic selection may lead to additional gains in recurrent selection program of P. maximum .

No abstract

RESUMO -Visando à liberação para uso comercial, realizou-se avaliação do capim-massai (Panicum maximum) quanto à adaptação e produtividade. No plantio foram utilizados 2,7 t/ha de calcário dolomítico, 500 kg/ha da fórmula 0-20-15 e 50 kg/ha de FTE BR-12. Como adubação de cobertura, efetuaram-se aplicações da fórmula 0-20-20 (200 kg/ha) The Panicum maximum cultivars tested were Mombaça and Massai. The experimental design was a randomized complete block with two treatments and two replicates. The paddocks (1.5 ha) were divided in six, and submitted to a rotational stocking with 7 days of grazing and 35 days of rest. Four steers (testers) were kept in each paddock for a whole year and additional steers were allocated and removed from each paddock to assure post-grazing residues higher than 2 t/ha of dry matter. All pastures were sampled, before and after grazing, to estimate forage availability, percentages of the morphological components and nutritive value. The animals were weighed each 42 days. Steers grazing Mombaça pasture performed better than those grazing Massai pasture, averaging 437 and 300 g/steer/day, respectively. However, the Massai pasture sustained higher stocking rate than the Mombaça pasture, with stocking rates of 2.15 and 1.86 AU/ha, respectively. This higher carrying capacity was not enough to compensate for the lower liveweight gain in the Massai pasture, resulting in lower productivity when compared to the Mombaça pasture, with averages of 626 and 691 kg/ha/year, respectively. The satisfactory performance presented by cv Massai, associated with other important characteristics of adaptability, attest the value of this cultivar as an alternative pasture for different beef cattle systems as well as a contribution to their sustainability.Key Words: animal performance, cultivar selection, forage accumulation, forage yield, stocking rate, nutritive value . IntroduçãoA manutenção de níveis de produção forrageira satisfatórios, compatíveis com o clima e as condições físico-químicas do solo de forma a manter o sistema sustentável ao longo do tempo constitui-se um dos grandes problemas da pecuária de corte. A busca da solução deste problema envolve não só a identificação de materiais forrageiros

RESUMO -O experimento foi conduzido para avaliar o coeficiente de repetibilidade de algumas características agronômicas em híbridos de Panicum maximum. Dez parcelas de plantas sexuais da espécie foram aleatoriamente distribuídas entre as 230 parcelas de acessos apomíticos. Após a fecundação natural, sementes de cada planta sexual constituíram-se uma família de meios-irmãos. Trinta plantas de cada progenitora foram avaliadas em delineamento de blocos ao acaso, com cinco plantas por parcela e seis repetições. A partir de cinco cortes, estimou-se o coeficiente de repetibilidade pelos métodos da Análise de Variância, Componentes principais (matriz de correlação e covariância) e Análise estrutural. Os coeficientes de repetibilidade (r) nos diferentes métodos, para todas as características avaliadas, oscilaram entre 0,51 e 0,86 e podem ser considerados altos, assim como os coeficientes de determinação. As estimativas do coeficiente de repetibilidade obtidas para as quatro características avaliadas pelo método da análise de variância foram quase sempre menores que as obtidas pelos demais métodos. Pelo método dos componentes principais (baseado na matriz de covariância), as estimativas foram sempre maiores em relação aos demais métodos. Considerando satisfatórios níveis de 80 ou 90% de confiabilidade para avaliação da superioridade relativa dos híbridos para todas as características avaliadas, as cinco medições realizadas são suficientes para escolha da melhor planta. A exclusão dos cortes 1 e 2 promove aumento nos coeficientes de repetibilidade e determinação.Palavras-chave: análise estrutural, análise de variância, componentes principais, produção de matéria seca Agronomic characters repeatability in Panicum maximum Jacq.ABSTRACT -The experiment was carried out to evaluate the coefficient of repeatability of some agronomic characteristics in Panicum maximum hybrids. Ten plots of sexual plants of this species were randomly distributed among 230 plots of apomitic accessions. After natural hybridization, seeds of each sexual plant constituted a half-sib family. Thirty plants of each female progenitor were evaluated in a randomized blocks design, with five plants per plot and six replications. Based on five evaluation cuts, the coefficient of repeatability was estimated by the methods analysis of variance, principal components (correlation and covariance matrices) and structural analyses. The coefficient of repeatability (r) estimated by the different methods, for all the characteristics evaluated, was high and varied from 0.51 to 0.86. The estimates of the coefficient of determination were also high. It was verified that the estimates of the repeatability coefficient for the four characteristics evaluated by the analyses of variance method were almost always smaller than the estimates obtained by the other methods. By the principal component method (based on the covariance matrix), the estimates were always the highest. Considering a level of 80 or 90% as satisfactory for the confidence in the decision of the relative su...