-It was studied the effects of shading (0, 36 and 54%) and of four nitrogen doses (0, 50, 100 and 150 mg N/dm 3 of soil) on the morphogenetic traits and on the tillering of grasses of Brachiaria genus (B. decumbens, B. ruziziensis and B. brizantha cv. Marandu and cv. Xaraes), cultivated in pots with 5 kg substrate. It was used a complete random design, in a 3 × 4 × 4 factorial scheme with three replications. Nitrogen promoted increase in leaf appearance rate and in average leaf blade length, whereas shading increased stem elongation rate. Leaf elongation rate and tillering varied with the interaction among shading percentages and nitrogen doses. Shading increased response efficiency of leaf elongation rate to nitrogen doses, but reduced for tillering, evidencing priority existing tillering growth in detriment to appearance of new tillers when there is light restriction for the plants. Phenotypic adjustments, in response to light reduction, indicate that the studied grasses present tolerance to moderate shading.

Resumo -O objetivo deste trabalho foi avaliar genótipos de capim-elefante (Pennisetum purpureum Schum.) quanto à resistência à cigarrinha-das-pastagens (Mahanarva spectabilis). Para avaliação da antibiose, aos trinta dias após o plantio, cada planta foi infestada com seis ovos próximos à eclosão, em delineamento inteiramente casualizado, com 30 genótipos e dez repetições. Quarenta e cinco dias após a eclosão das ninfas, avaliou-se a porcentagem de sobrevivência do inseto-praga nos diferentes genótipos. Para avaliação da não-preferência, foram quantificados, quinzenalmente, o número e tamanho de ninfas por vaso, em plantas mantidas em casa de vegetação, onde adultos de M. spectabilis eram periodicamente liberados, em delineamento inteiramente casualizado, com três repetições por genótipo, em dois períodos de amostragem. Os genótipos Cameroon de Piracicaba, Pioneiro, Cuba 169, Santa Rita, Mineiro Ipeaco, Mercker Comum de Pinda e CNPGL 96-27-3 foram selecionados quanto à resistência, pelo mecanismo de antibiose. O número e o tamanho médio das ninfas variaram significativamente em razão do genótipo de capim-elefante, no estudo da não-preferência. Os genótipos Roxo de Botucatu e Pioneiro são candidatos à testemunha suscetível e resistente, respectivamente, pelo mecanismo de antibiose, e os genótipos Cameroon e Cameroon Piracicaba são promissores pelo mecanismo de não-preferência.Termos para indexação: Pennisetum purpureum, Mahanarva spectabilis, resistência a pragas, forrageiras, antibiose, não-preferência. Selection of elephant grass genotypes for resistance to spittlebugAbstract -The objective of this work was to evaluate genotypes of elephant grass (Pennisetum purpureum Schum.) regarding resistance to the spittlebug Mahanarva spectabilis. For antibiosis evaluation, each plant was infested with six eggs near hatching, thirty days after planting, in a completely randomized design with 30 genotypes and ten repetitions. Forty-five days after the nymphs hatched, the insect survival rate was evaluated on the different genotypes. For nonpreference mechanism evaluation, the size and number of the nymphs per pot were assessed every 15 days, in plants kept at greenhouse, where adults of M. spectabilis were periodically released, in a completely randomized design, with three repetitions per genotype in two sampling periods. Cameroon de Piracicaba, Pioneiro, Cuba 169, Santa Rita, Mineiro Ipeaco, Mercker Comum de Pinda and CNPGL 96-27-3 genotypes were selected for resistance, by antibiosis mechanism. In the study of the nonpreference mechanism, the number and average size of the nymphs varied significantly as a function of the elephant grass genotype. Roxo de Botucatu and Pioneiro genotypes are, respectively, susceptible and resistant check candidates by the antibiosis mechanism, and Cameroon and Cameroon Piracicaba genotypes are promising by the nonpreference mechanism.

Pasture is the main food source for more than 200 million cattle heads in Brazil. Although Brazilian forage breeding programs have successfully released well-adapted, high-yielding cultivars over the years, the use of genomic tools in these programs is currently limited. These tools are required to tackle the main challenges for tropical forage breeding in Brazil. In this context, this note lists the main research priorities raised at the workshop "Breeding Forages in the Genomic Era", which are necessary to accelerate the use of genomic tools for next-generation breeding of tropical forages and allow breeders to increase genetic gains. Additionally, an online discussion forum (hosted at http://www. cnpgl.embrapa.br/genfor) has been launched to strengthen collaborations among research groups. The research priorities and more synergistic collaborations will assist researchers and decision-makers in delivering a sustainable increase in production of animal products, especially beef and milk, which are required to feed a rising world population.

RESUMOObjetiva-se com este trabalho estimar a repetibilidade para caracteres forrageiros de Panicum, e determinar o número de cortes de avaliação necessários para a seleção de genótipos de Panicum, com confiabilidade. Utilizaram-se os dados de um ensaio conduzido no período de 21/11/2002 a 08/04/2005, no Campo Experimental da Embrapa Gado de Leite, localizado em Valença-RJ, onde foram realizados 15 cortes de avaliação. No ensaio, foram avaliados 23 genótipos de Panicum maximum, em parcelas experimentais, dispostas no delineamento de blocos casualizados, com três repetições. Foram estimados os coeficientes de repetibilidade para as características produção de matéria verde de forragem (PMV); produção de matéria seca de forragem (PMS) e de folhas (PMSF); porcentagem de folhas na PMS (%FOL) e altura da planta (AP), utilizando os métodos da análise de variância, componentes principais e análise estrutural. Para todas as características avaliadas os efeitos de genótipos, cortes e interação genótipos x cortes foram significativos (P<0,01). Quando se considerou o coeficiente de determinação de 85%, o número de avaliações (cortes) necessários para a determinação do valor real dos genótipos foram de 10, 9, 7, 11 e 3, respectivamente, para PMV, PMS, PMSF, %FOL e AP. O método dos componentes principais e o da análiseestrutural (baseado na matriz de correlações) foram concordantes para todas as características avaliadas. A realização de 10 cortes de avaliação permite discriminar o valor real dos genótipos de Panicum, com confiabilidade superior a 85%, para a maioria das características avaliadas.Termos para indexação: Forrageira, gramínea, componentes principais, análise estrutural, coeficiente de repetibilidade. ABSTRACTThe objective of this work was to estimate the repeatability for forage characters of Panicum and to determinate the necessary number of evaluation cuts to select Panicum genotypes with confidence. Data of a trial with 15 cuts, carried out between 21/11/2002 and 08/04/2005 in the experimental station of Embrapa Gado de Leite located in Valença, RJ, Brazil, were used. In this study. 23 genotypes of Panicum maximum were evaluated, in a complete randomized block, with three replications. The coefficient of repeatability for fresh forage production (PMV), total plant dry matter production (PMS) and leaves dry matter production (PMSF) were recorded along with leaves percentage in PMS (%FOL) and plant hight (AP), using the variance analysis, main components and structural analysis methods. For all evaluated parameters the effects of genotype, cut and genotype x cut interaction were significant (P<0.01). When considering the determination coefficient as 85%, the required number of measures (cuts) to determine the real value of genotypes were 10, 9, 7, 11 and 3, for PMV, PMS, PMSF, %FOL and AP, respectively. Main components and structural analysis methods (based on the correlation matrix) did agree for all features evaluated. The utilization of data from 10 cuts allows to discriminate, with confidence higher than 8...

-The objective of the present work was to induce chromosome doubling in genotypes of Brachiaria ruziziensis with potential for production of good-quality biomass and tolerance/resistance to stress caused by aluminum and spittlebugs. Germinated seeds of B. ruziziensis were immersed in 0.1% colchicine solution for 2 or 3 hours. Ploidy level was determined by flow cytometry and confirmed by chromosome count. Fertility of the tetraploid plants was assessed through evaluation of pollen viability by staining. There was no statistical difference with regard to seedling survival and number of duplicate seedlings between the treatments. Survival rate was 8%, of which 11.45% were tetraploid genotypes. The mean viability of pollen grains from the evaluated tetraploid plants ranged from 51.75 to 55.50%. So, the tetraploids plants obtained from genotypes of a bred population of ruzigrass produce fertile pollen, in percentages that render crosses viable in genetic breeding programs.

1769 RESEARCH B rachiaria (Trin.) Griseb. is a genus belonging to the family Poaceae Barnh., tribe Paniceae Rchb. that aggregates approximately 100 species with considerable forage value and that are native to tropical and subtropical regions of Africa (Keller-Grein et al., 1996).In Brazil, the introduction of the genus began with Brachiaria decumbens Stapf, where its dispersal was favored in several parts of the country. Other species were introduced later, from the 1960s to the mid-1970s, and the genus spread across the Brazilian Cerrado in subsequent years (Mitidieri, 1988).It is estimated that there are 100 million hectares of cultivated pasture and another 70 million hectares of naturalized pasture land in Brazil that are dominated by Brachiaria on approximately 85% of those areas (IBGE, 2006). The species of Brachiaria are arranged in groups according to perceived natural affinities related to the morphology of the inflorescence, especially the spikelet. Two groups of greatest economic importance for the country include: (i) Brachiaria decumbens, Brachiaria brizantha (Hochst. ex A. Rich.) Stapf, and Brachiaria ruziziensis R. Germ. & C.M. Evrard, and (ii) Brachiaria humidicola (Rendle) Schweick., Brachiaria dictyoneura (Fig. and De Not.) Stapf, and Brachiaria jubata (Fig. and De Not.) Stapf (Renvoize et al. , 1996).The taxonomy of the genus is complex due to the continuous variation of traits used to delimit species and related genera ABSTRACT Brachiaria (Trin.) Griseb. is a genus belonging to the Poaceae Barnh. family that aggregates species of forage interest, which have shown different levels of ploidy, intraspecific variability for chromosomal morphology and for number of rDNA sites. This study aimed at characterizing the karyotype of Brachiaria brizantha (Hochst. ex A. Rich) Stapf, Brachiaria decumbens Stapf, and Brachiaria ruziziensis R. Germ. & C.M. Evrard by the location of 5S rDNA, 45S rDNA, centromeric retrotransposons, chromomycin A3 (CMA) and 4¢, 6-diamidino-2-phenylindole dihydrochloride (DAPI) chromosome bands,and transcriptional activity at nucleolar organizing regions (NORs). Brachiaria ruziziensis has 2n = 2x = 18 chromosomes, karyotypic formula 9M, one 45S rDNA site, and two 5S rDNA sites. Brachiaria brizantha has 2n = 4x = 36 chromosomes, karyotypic formula 18M, four to six 5S rDNA signals, and two to four 45S rDNA sites. One of the chromosomes carrying 45S rDNA is heteromorphic. Brachiaria decumbens has 2n = 4x = 36 chromosomes, karyotypic formula 17M+1M/SM, and seven 5S rDNA signals including one hemizygous 5S rDNA locus. One of the two chromosome pairs carrying 45S rDNA signals was heteromorphic with one of its chromosomes possessing a tertiary constriction. Hybridization signals with a centromeric retrotransposon probe, CRM1, were observed in Brachiaria chromosomes with distinct clusters on all B. ruziziensis chromosomes. Chromosomal CMA bands were located along with 45S rDNA signals in B. decumbens and B. ruziziensis whereas in B. brizantha only two out of four signals coincided. The ...

The aim of this study was to evaluate the resistance of B. ruziziensis clones to the spittlebug species Deois schach and Mahanarva spectabilis. Together with the cultivar Marandu (B. brizantha) and the progenies 77s, 85s and 106s as controls, 71 B. ruziziensis clones were evaluated in a randomized block design. Six spittlebug eggs about to hatch were artificially infested and 40 days later evaluated for the percentage of surviving nymphs and plant damage based on a rating scale. Analysis of variance identified significant differences for nymph survival and plant damage of both spittlebug species.

Resumo -O objetivo deste trabalho foi avaliar a suscetibilidade diferencial de espécies de Urochloa ao herbicida glifosato. Dois experimentos foram implantados na Embrapa Gado de Leite, em Juiz de Fora, MG. O primeiro experimento foi realizado em vasos dispostos em bancadas, em ambiente aberto, e o segundo em campo. Em ambos os experimentos, adotou-se o delineamento experimental em blocos ao acaso, com parcelas subdivididas. Nas parcelas, foram semeadas três espécies de braquiária (U. brizantha, U. decumbens e U. ruziziensis) e, nas subparcelas, foram dispostas as doses do equivalente ácido do herbicida glifosato (0, 180, 360, 540, 720, 1.080, 1.440 g ha -1 ). Há variabilidade entre as espécies avaliadas de Urochloa, quanto à suscetibilidade ao herbicida glifosato, e U. ruziziensis é a mais suscetível. O conhecimento da suscetibilidade diferencial entre as espécies de Urochloa avaliadas permite uma economia de 12 a 16% na dose do herbicida glifosato.Termos para indexação: Brachiaria, Urochloa, dessecação, forrageiras, integração lavoura-pecuária, plantio direto. Differential susceptibility of brachiaria species to glyphosateAbstract -The objective of this work was to evaluate the differential susceptibility of Urochloa species to glyphosate. Two experiments were carried out at Embrapa Gado de Leite, in Juiz de Fora, Minas Gerais state, Brazil. The first experiment was carried out in pots placed on benches in an open environment, and the second one in the field. A randomized block design arranged in split plot was used for both experiments. Three species of brachiaria (U. brizantha, U. decumbens and U. ruziziensis) were sown in the plots, and the subplots consisted of the glyphosate acid equivalent doses (0, 180, 360, 540, 720, 1,080, and 1,440 g ha -1 ). There is variability among the evaluated Urochloa species regarding glyphosate susceptibility, and U. ruziziensis is the most susceptible. The knowledge on the differential susceptibility among the evaluated Urochloa species allows for a saving from 12 to 16% herbicide glyphosate dose.Index terms: Brachiaria, Urochloa, desiccation, forage grasses, crop-livestock integration, no-till. IntroduçãoA cobertura vegetal da superfície do solo, antes da semeadura das culturas, é fundamental para a implantação do sistema plantio direto (Ruedell, 1995). Assim, o emprego de espécies com elevada produtividade de fitomassa é um dos fatores para que se alcance sucesso nesse sistema.Em regiões como a do Cerrado brasileiro, onde o inverno é seco, com fotoperíodo curto, há certa dificuldade em se produzir grande quantidade de palha. Além disso, o início das chuvas na região causa rápida decomposição da palha, em razão do aumento da umidade e da temperatura. Trabalhos de pesquisa têm demonstrado que a maior limitação para a manutenção da palha sobre o solo, em regiões de clima tropical, é a rapidez com que a massa vegetal se decompõe (Pereira, 1990;Landers, 1995). Por essa razão, resíduos com maior relação C/N (carbono/nitrogênio), como os de plantas de cobertura, podem ser utili...