Liana Jank

Breeding tropical forages

Brazil has the largest commercial beef cattle herd and is the main beef exporter in the world. Cultivated pastures are the basis for the Brazilian beef production, and occupy an area of 101.4 million hectares. However, very few forage cultivars are commercially available, and the majority of these ar e of apomictic reproduction, thus genetically homogeneous. T ropical forage breeding is at its infancy, but much investment and efforts have been applied in the last three decades and some new cultivars have been released. In this paper, origin of different species, modes of reproduction, breeding programs and targets are discussed and the resulting new cultivars released are presented.

Produção de gramíneas do gênero Brachiaria sob níveis de sombreamento

O trabalho foi realizado com o objetivo de avaliar a producao de B. decumbens cv. Basilisk e B. brizantha, cultivares Marandu e Xaraes, sob diferentes niveis de sombreamento. Utilizou-se delineamento em blocos casualizados com esquema de parcelas subdivididas, considerando os niveis de sombreamento (0, 50, 70%) como parcela e as especies ou cultivares como subparcelas. Sementes das gramineas foram postas a germinar em bandejas e transplantadas (tres plântulas por vaso). Foram realizados quatro cortes em cada subparcela. Antes de cada corte, mediram-se a altura de planta e a area foliar de quatro folhas em cada planta e quantificou-se o numero de perfilhos vivos por vaso. Apos a colheita, as plantas foram separadas em lâmina, colmo + bainha e material morto para determinacao da producao de materia seca. Para producao de materia seca total, calcularam-se a producao media em cada um os cortes e a producao total. No ultimo corte, avaliou-se a massa seca de raizes. As interacoes significativas foram desdobradas adequadamente. O fator qualitativo foi submetido a comparacao de medias pelo teste Tukey e o quantitativo a analise de regressao linear. A excecao da producao media em quatro cortes e da producao de colmos e de material morto, observou-se interacao significativa para todas as outras variaveis. Independentemente do nivel de sombreamento, o cultivar Xaraes destacou-se positivamente na maioria das caracteristicas analisadas, enquanto, no nivel de 50% de sombreamento, o capim-braquiaria apresentou maior produtividade, em porcentagem de producao a pleno sol. Na avaliacao da porcentagem de folhas, destacou-se o capim-xaraes, seguido do capim-marandu. Independentemente da forrageira, o nivel de sombreamento teve efeito direto sobre o numero de perfilhos/planta, a producao de MS do sistema radicular, a area foliar e o valor SPAD.

The value of improved pastures to Brazilian beef production

Abstract. 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.

Breeding Panicum maximum in Brazil. 1. Genetic resources, modes of reproduction and breeding procedures

SummaryApomixis is widely distributed among tropical forage grasses, and has long been merely regarded as an impediment to breeding. Panicum maximum is presented as the first opportunity for Brazilian geneticists to develop and test original breeding schemes adapted to an apomictic species.A large and representative germplasm of P. maximum has been introduced and is currently being evaluated. Basic knowledges on biology and reproduction are also available, which demonstrate an easy manipulation of apomixis and sexuality. Several limiting traits have already been detected during evaluation, which justify breeding attempts. An ideal scheme is given to transfer new qualities to already selected varieties.

Avaliação dos capins mombaça e massai sob pastejo

A new cultivar of Panicum maximum (Massai) was evaluated for commercial release, at the Embrapa Beef Cattle, Campo Grande, MS, Brazil, from November 1993 to April 1999. At establishment, 2,7 t/ha of lime, 400 kg/ha of 0-20-20 and 50 kg/ha of FTE were applied. Maintenance fertilizer was 200 kg/ha of 0-20-20 NPK and 50 kg/ha N, annually. The Panicum maximum cultivars tested were Mombaca 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 Mombaca 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 Mombaca 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 Mombaca 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.

Repetibilidade de caracteres agronômicos em Panicum maximum Jacq.

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 superiority of the hybrids based on green matter yield, these five evaluation cuts would be sufficient for the choice of the best plant. The exclusion of the first two cuts will increase the repeatability and determination coefficients.

Análise biométrica e seleção de progênies tetraplóides de Panicum maximum usando os métodos de modelos mistos

The objectives of this work were to estimate the genetic and phenotypic parameters and to predict the genetic and genotypic values of the selection candidates obtained from intraspecific crosses in Panicum maximum as well as the performance of the hybrid progeny of the existing and projected crosses. Seventy-nine intraspecific hybrids obtained from artificial crosses among five apomictic and three sexual autotetraploid individuals were evaluated in a clonal test with two replications and ten plants per plot. Green matter yield, total and leaf dry matter yields and leaf percentage were evaluated in five cuts per year during three years. Genetic parameters were estimated and breeding and genotypic values were predicted using the restricted maximum likelihood/best linear unbiased prediction procedure (REML/BLUP). The dominant genetic variance was estimated by adjusting the effect of full-sib families. Low magnitude individual narrow sense heritabilities (0.02-0.05), individual broad sense heritabilities (0.14-0.20) and repeatability measured on an individual basis (0.15-0.21) were obtained. Dominance effects for all evaluated characteristics indicated that breeding strategies that explore heterosis must be adopted. Less than 5% increase in the parameter repeatability was obtained for a three-year evaluation period and may be the criterion to determine the maximum number of years of evaluation to be adopted, without compromising gain per cycle of selection. The identification of hybrid candidates for future cultivars and of those that can be incorporated into the breeding program was based on the genotypic and breeding values, respectively. The prediction of the performance of the hybrid progeny, based on the breeding values of the progenitors, permitted the identification of the best crosses and indicated the best parents to use in crosses.

De novo transcriptome assembly for the tropical grass Panicum maximum Jacq.

Guinea grass (Panicum maximum Jacq.) is a tropical African grass often used to feed beef cattle, which is an important economic activity in Brazil. Brazil is the leader in global meat exportation because of its exclusively pasture-raised bovine herds. Guinea grass also has potential uses in bioenergy production due to its elevated biomass generation through the C4 photosynthesis pathway. We generated approximately 13 Gb of data from Illumina sequencing of P. maximum leaves. Four different genotypes were sequenced, and the combined reads were assembled de novo into 38,192 unigenes and annotated; approximately 63% of the unigenes had homology to other proteins in the NCBI non-redundant protein database. Functional classification through COG (Clusters of Orthologous Groups), GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analyses showed that the unigenes from Guinea grass leaves are involved in a wide range of biological processes and metabolic pathways, including C4 photosynthesis and lignocellulose generation, which are important for cattle grazing and bioenergy production. The most abundant transcripts were involved in carbon fixation, photosynthesis, RNA translation and heavy metal cellular homeostasis. Finally, we identified a number of potential molecular markers, including 5,035 microsatellites (SSRs) and 346,456 single nucleotide polymorphisms (SNPs). To the best of our knowledge, this is the first study to characterize the complete leaf transcriptome of P. maximum using high-throughput sequencing. The biological information provided here will aid in gene expression studies and marker-assisted selection-based breeding research in tropical grasses.

Asynchronous meiosis in an interspecific hybrid of Brachiaria ruziziensis and B. brizantha

Male meiosis is generally synchronous in higher plants. The regulation of the cell cycle is still not well understood, and a powerful tool for gaining an understanding of this regulation is the development of mutations that affect cell-cycle synchrony. We report here asynchronous microsporogenesis in an interspecific hybrid between two important tropical grasses. In young spikelets of the interspecific hybrid 49.10% of anther meiocytes entered meiosis, exhibiting typical phases of the first and second divisions, while the other 50.90% showed distinctive features of early prophase. In older spikelets, anthers containing mature pollen grains also displayed meiocytes still undergoing meiosis. At this time, the latter cells were enclosed by the exine wall. Despite asynchrony, all cells completed meiosis. Old anthers contained only pollen grains that appeared to be in the same stage of development. Pollen fertility was estimated to be 52.76% in dehiscent anthers. An independent genetic control for meiosis synchrony and meiotic stages is suggested.

Estimativas de repetibilidade para caracteres forrageiros em Panicum maximum

Objetiva-se com este trabalho estimar a repetibilidade para caracteres forrageiros de Panicum, e determinar o numero de cortes de avaliacao necessarios para a selecao de genotipos de Panicum, com confiabilidade. Utilizaram-se os dados de um ensaio conduzido no periodo de 21/11/2002 a 08/04/2005, no Campo Experimental da Embrapa Gado de Leite, localizado em Valenca-RJ, onde foram realizados 15 cortes de avaliacao. No ensaio, foram avaliados 23 genotipos de Panicum maximum, em parcelas experimentais, dispostas no delineamento de blocos casualizados, com tres repeticoes. Foram estimados os coeficientes de repetibilidade para as caracteristicas producao de materia verde de forragem (PMV); producao de materia seca de forragem (PMS) e de folhas (PMSF); porcentagem de folhas na PMS (%FOL) e altura da planta (AP), utilizando os metodos da analise de variância, componentes principais e analise estrutural. Para todas as caracteristicas avaliadas os efeitos de genotipos, cortes e interacao genotipos x cortes foram significativos (P<0,01). Quando se considerou o coeficiente de determinacao de 85%, o numero de avaliacoes (cortes) necessarios para a determinacao do valor real dos genotipos foram de 10, 9, 7, 11 e 3, respectivamente, para PMV, PMS, PMSF, %FOL e AP. O metodo dos componentes principais e o da analiseestrutural (baseado na matriz de correlacoes) foram concordantes para todas as caracteristicas avaliadas. A realizacao de 10 cortes de avaliacao permite discriminar o valor real dos genotipos de Panicum, com confiabilidade superior a 85%, para a maioria das caracteristicas avaliadas.