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Artificial hybridization plays a fundamental role in plant breeding programs since it generates new genotypic combinations that can result in desirable phenotypes. Depending on the species and mode of reproduction, controlled crosses may be challenging, and contaminating individuals can be introduced accidentally. In this context, the identification of such contaminants is important to avoid compromising further selection cycles, as well as genetic and genomic studies. The main objective of this work was to propose an automated multivariate methodology for the detection and classification of putative contaminants, including apomictic clones (ACs), self-fertilized individuals, half-siblings (HSs), and full contaminants (FCs), in biparental polyploid progenies of tropical forage grasses. We established a pipeline to identify contaminants in genotyping-by-sequencing (GBS) data encoded as allele dosages of single nucleotide polymorphism (SNP) markers by integrating principal component analysis (PCA), genotypic analysis (GA) measures based on Mendelian segregation, and clustering analysis (CA). The combination of these methods allowed for the correct identification of all contaminants in all simulated progenies and the detection of putative contaminants in three real progenies of tropical forage grasses, providing an easy and promising methodology for the identification of contaminants in biparental progenies of tetraploid and hexaploid species. The proposed pipeline was made available through the polyCID Shiny app and can be easily coupled with traditional genetic approaches, such as linkage map construction, thereby increasing the efficiency of breeding programs. Made available in DSpace on 2021-12-07T14:00:42Z (GMT). No. of bitstreams: 1 SemiAutomatedSNP.pdf: 2844859 bytes, checksum: e7cb8fd79620358847aaa86717df754b (MD5) Previous issue date: 2021

Urochloa decumbens (Stapf) R. D. Webster is one of the most important African forage grasses in Brazilian beef production. Currently available genetic-genomic resources for this species are restricted mainly due to polyploidy and apomixis. Therefore, crucial genomic-molecular studies such as the construction of genetic maps and the mapping of quantitative trait loci (QTLs) are very challenging and consequently affect the advancement of molecular breeding. The objectives of this work were to (i) construct an integrated U. decumbens genetic map for a full-sibling progeny using GBS-based markers with allele dosage information, (ii) detect QTLs for spittlebug (Notozulia entreriana) resistance, and (iii) seek putative candidate genes involved in defense against biotic stresses. We used the Setaria viridis genome a reference to align GBS reads and selected 4,240 high-quality SNP markers with allele dosage information. Of these markers, 1,000 were distributed throughout nine homologous groups with a cumulative map length of 1,335.09 cM and an average marker density of 1.33 cM. We detected QTLs for resistance to spittlebug, an important pasture insect pest, that explained between 4.66 and 6.24% of the phenotypic variation. These QTLs are in regions containing putative candidate genes related to defense against biotic stresses. Because this is the first genetic map with SNP autotetraploid dosage data and QTL detection in U. decumbens, it will be useful for future evolutionary studies, genome assembly, and other QTL analyses in Urochloa spp. Moreover, the results might facilitate the isolation of spittlebug-related candidate genes and help clarify the mechanism of spittlebug resistance. These approaches will improve selection efficiency and accuracy in U. decumbens molecular breeding and shorten the breeding cycle. Made available in DSpace on 2019-03-02T00:39:40Z (GMT). No. of bitstreams: 1 Geneticmappingwithaleledosageinformation.pdf: 9740583 bytes, checksum: 73a6f7b51cee1e27ffa3a10bd91674d0 (MD5) Previous issue date: 2019-02-27

Ainda há muitas cultivares por vir, cada uma com vantagens específicas. A tendência é que sejam liberadas espécies menos generalistas, sou seja, adaptadas às demandas específicas do setor produtivo.

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. Made available in DSpace on 2019-03-02T00:39:17Z (GMT). No. of bitstreams: 1 Contributionofadditiveanddominance.pdf: 2450457 bytes, checksum: 7aa7041ae330dbbeed09ec5a8c4f1f52 (MD5) Previous issue date: 2019-02-27

In this study, the aim was to determine the influence of potassium nitrate, using different concentrations and immersion times on the dormancy of the seeds of Brachiaria humidicola cv. ‘BRS Tupi’. Four experiments were performed adopting a factorial scheme (5x3+1) in different seed lots, for different post-harvest storage durations, during which the seeds were immersed in potassium nitrate solutions of different specific concentrations (0, 0.1, 0.3, 0.5 and 1% KNO3), for three exposure periods (12, 24 and 48h), plus one control (untreated), in a completely randomized design. The characteristics assessed included the imbibition curve, germination, first count and germination rate, as well as viability confirmed by using tetrazolium test. From the findings it was evident that treatments involving 0.1; 0.3; 0.5 and 1% KNO3 or pure water, with a 12 hour-soaking period enabled the stored seeds to germinate well for a minimum of eight months post harvest. Root protrusion was observed 24 hours post seed imbibition, whereas for the untreated seeds, satisfactory germination was observed from at least 12 months post harvest and, in most of the lots, between 18 and 24 months. RESUMO: Objetivou-se avaliar os efeitos do nitrato de potássio, em diferentes concentrações e períodos de imersão, na superação da dormência de sementes de Brachiaria humidicola cv. ‘BRS Tupi’. Os experimentos, em número de quatro, foram realizados com diferentes lotes de sementes, em esquema fatorial (5x3+1) em diferentes períodos de armazenamento após a colheita, em que os tratamentos consistiram de imersão das sementes em soluções com diferentes concentrações de nitrato de potássio (0; 0,1; 0,3; 0,5 e 1% de KNO3), por três períodos de exposição (12, 24 e 48h), mais uma testemunha (sem tratamento), em delineamento inteiramente casualisado. As características avaliadas foram: curva de embebição, germinação, primeira contagem e índice de velocidade de germinação e viabilidade pelo teste de tetrazólio. Os tratamentos 0,1; 0,3; 0,5 e 1% de KNO3 ou água pura, com período de embebição por 12 horas, proporcionam germinação satisfatória das sementes armazenadas por, no mínimo, oito meses após a colheita. A partir de 24h de embebição das sementes ocorre protrusão radicular, enquanto para as sementes não tratadas a germinação satisfatória ocorre, no mínimo, a partir de 12 meses da colheita e, na maioria dos lotes, de 18 a 24 meses.

The autotetraploid forage Congo signal grass (Brachiaria ruziziensis) is an important component in the Brachiaria breeding programme. As with other tropical forage grass species, the association between flowering and seed yield components, the mode of inheritance and the effects of population structure on phenotypic breeding are lacking. Seventeen characteristics evaluated in 59 half-sib progeny of seven subpopulations were analysed using a mixed model methodology. According to the commonality analysis, the total seed yield (0.67) and number of days to flowering (0.22) had a greater influence on the filled-seed yield. The flowering synchrony, total number of panicles, filled-seed yield, green matter yield and dry matter yield presented statistically significant additive genetic variance between and within the subpopulations. The QST estimates ranged from 0.09 for the flowering synchrony index to 0.31 for the filled-seed yield. The effects of population structure and its use in breeding programmes are further discussed.

This study aimed to evaluate aspects of reproductive phenology, yield components and seed quality of the B4 genotype of Brachiaria brizantha in function of nitrogen doses applied at pre-flowering. The experiment was carried out at Embrapa Beef Cattle, in a randomized block design, with seeding density of 2.59kg SPV ha-1 in the first year, in free growth plants. Urea was applied at pre-flowering at doses of 0, 25, 50, 75, 100, 125 and 150kg ha-1. The reproductive cycle of the plant lasts 225 days, with late flowering. N doses influenced the following characteristics: number of fully expanded inflorescences, percentage of dry matter, dry biomass, number of spikelets per raceme, seed yield, weight of a thousand seeds, germination, germination speed index, viability and germination at 10 months after harvest. The maximum yield of pure seed was 144.8kg ha-1 for 50kg ha-1 N, with maximum biological potential, based on components of seed yield of 456.27kg ha-1. Seeds presented high dormancy and reduced physiological quality in higher N doses. Made available in DSpace on 2018-02-21T00:39:21Z (GMT). No. of bitstreams: 1 15ProductivityandqualityofBrachiariabrizanthaB4seedsinfunctionofnitrogendoses2016.pdf: 284946 bytes, checksum: a2a35ee1843a2fda2ccd2314c6ea0b04 (MD5) Previous issue date: 2018-02-20 Título em português: Produtividade e qualidade de sementes de Brachiaria brizantha B4 em função de doses de nitrogênio.

The objective of this study was to estimate genetic parameters for agronomic traits and nutritional value in intraspecific hybrids of B. decumbens. For this, a population of 1,415 hybrids was evaluated in field plots at Embrapa Beef Cattle in Campo Grande/MS/Brazil, with seven clippings in order to estimate field green weight (FGW); total dry matter (TDM); speed of regrowth (SR); tiller regrowth density (TRD); regrowth ability (REG); crude protein (CP); in vitro organic matter digestibility (IVD); neutral detergent fiber (NDF) and lignin (LIG). The statistical analyses were carried out using the mixed models methods. Genetic variability for all traits assessed was detected, and estimates of individual heritability were of medium to high magnitude, indicating the possibility of gains with selection. Significant genetic correlations were observed between FGW and TDM (0.99), TDM and SR (0.81), TDM and IVD (-0.71), TDM and LIG (0.71), and CP and IVD (0.70). Made available in DSpace on 2018-02-27T00:42:00Z (GMT). No. of bitstreams: 1 62EstimateofgeneticparametersinBrachiariadecumbenshybrids2016.pdf: 318117 bytes, checksum: 1a60cb4ce3ed862b0687b47ed3978e88 (MD5) Previous issue date: 2018-02-26

Half-sib progenies of congo signal grass (Brachiaria ruziziensis Germain & Evrard, syn.: B. eminii, Urochloa ruziziensis) were analysed using a mixed model methodology. The objective was to estimate genetic and phenotypic parameters, predict individual genetic values, estimate correlations between characters associated with biomass production and forage nutritive value and use this information to determine the economic weights to compare three multiplicative selection indices. Individual narrow-sense heritabilities corrected for inbreeding varied from 0.14 to 0.91 for characters associated with biomass production and from 0.04 a 0.24 for nutritional value characters. The correlations among characters associated with annual biomass production were of high magnitude. In contrast, biomass production characters were negatively correlated with crude protein, acid detergent fibre and lignin. Total dry matter yield, crude protein and regrowth ability were weighted separately in evaluations during wet and dry season or annually in selection indices. Index that considered characters annually resulted in better distribution of forage production along the year than indices that separated wet and dry season production.

Background: Forage grasses of the African genus Urochloa (syn. Brachiaria) are the basis of Brazilian beef production, and there is a strong demand for high quality, productive and adapted forage plants. Among the approximately 100 species of the genus Urochloa, Urochloa decumbens is one of the most important tropical forage grasses used for pastures due to several of its agronomic attributes. However, the level of understanding of these attributes and the tools with which to control them at the genetic level are limited, mainly due to the apomixis and ploidy level of this species. In this context, the present study aimed to identify and characterize molecular microsatellite markers of U. decumbens and to evaluate their cross-amplification in other Urochloa species. Findings: Microsatellite loci were isolated from a previously constructed enriched library from one U. decumbens genotype. Specific primers were designed for one hundred thirteen loci, and ninety-three primer pairs successfully amplified microsatellite regions, yielding an average of 4.93 alleles per locus. The polymorphism information content ( IC) values of these loci ranged from 0.26 to 0.85 (average 0.68), and the associated discriminating power (DP) values ranged from 0.22 to 0.97 (average 0.77). Cross-amplification studies demonstrated the potential transferability of these microsatellites to four other Urochloa species. Structure analysis revealed the existence of three distinct groups, providing evidence in the allelic pool that U. decumbens is closely related to Urochloa ruziziensis and Urochloa brizantha. The genetic distance values determined using Jaccard?s coefficient ranged from 0.06 to 0.76. Conclusions: The microsatellite markers identified in this study are the first set of molecular markers for U. decumbens species. Their availability will facilitate understanding the genetics of this and other Urochloa species and breeding them, and will be useful for germplasm characterization, linkage mapping and marker-assisted selection. Keywords: Enriched library, Forage, Signalgrass, Simple sequence repeat, Transferability

Brachiaria decumbens has great importance in the national beef cattle scenario due to its high forage yield potential and high adaptability to acid soils and low fertility. In order to obtain new cultivars, intraspecific hybrids, previously selected by the Brachiaria breeding program, were evaluated in 2013 and 2014 for phenological characteristics and seed production potential through their production components, aiming to obtain cultivars with satisfactory production agronomic characteristics and forage yield, resistant to ?cigarrinhas-das-pastagens? (Tomaspia sp.) and good seed production. Estimates of phenotypic correlation and analysis of variance were performed using the SAS 9.3 software. From the results obtained in both consecutive years, it was observed that there was a correlation between the reproductive tiller number (RT) and the pure seeds (PS) weight in the seedbeds of the second year of production around 70% (p < 0.01), which can be considered as a parameter to estimate the production of pure seeds before the start of flowering. Made available in DSpace on 2018-02-21T00:39:53Z (GMT). No. of bitstreams: 1 16Brachiariadecumbensintraspecifichybridscharacterizationandselectionforseedproduction2016.pdf: 681543 bytes, checksum: 9da119729a0aa80a579d9cf2df239180 (MD5) Previous issue date: 2018-02-20 Título em português: Híbridos intraespecíficos de Brachiaria decumbens: caracterização e seleção para produção de sementes.

The African species Urochloa humidicola (Rendle) Morrone & Zuloaga (syn. Brachiaria humidicola (Rendle) Schweick.) is an important perennial forage grass found throughout the tropics. This species is polyploid, ranging from tetra to nonaploid, and apomictic, which makes genetic studies challenging; therefore, the number of currently available genetic resources is limited. The genomic architecture and evolution of U. humidicola and the molecular markers linked to apomixis were investigated in a full-sib F1 population obtained by crossing the sexual accession H031 and the apomictic cultivar U. humidicola cv. BRS Tupi, both of which are hexaploid. A simple sequence repeat (SSR)-based linkage map was constructed for the species from 102 polymorphic and specific SSR markers based on simplex and double-simplex markers. The map consisted of 49 linkage groups (LGs) and had a total length of 1702.82 cM, with 89 microsatellite loci and an average map density of 10.6 cM. Eight homology groups (HGs) were formed, comprising 22 LGs, and the other LGs remained ungrouped. The locus that controls apospory (apo-locus) was mapped in LG02 and was located 19.4 cM from the locus Bh027.c.D2. In the cytological analyses of some hybrids, bi- to hexavalents at diakinesis were observed, as well as two nucleoli in some meiocytes, smaller chromosomes with preferential allocation within the first metaphase plate and asynchronous chromosome migration to the poles during anaphase. The linkage map and the meiocyte analyses confirm previous reports of hybridization and suggest an allopolyploid origin of the hexaploid U. humidicola. This is the first linkage map of an Urochloa species, and it will be useful for future quantitative trait locus (QTL) analysis after saturation of the map and for genome assembly and evolutionary studies in Urochloa spp. Moreover, the results of the apomixis mapping are consistent with previous reports and confirm the need for additional studies to search for a co-segregating marker.

Tetraploid Brachiaria ruziziensis genotypes which reproduce sexually are essential for the breeding of other species of the Brachiaria genus which reproduce by apomixis. Aiming at studying the available phenotypic and genetic variability in the breeding population of B. ruziziensis, it was estimated the parameters heritability and genetic and phenotypic correlations between the traits associated with flowering, and the traits responsible for forage yield and nutritional quality. Seventeen traits in 1180 individuals from 59 open pollinated families were studied, and the data were analyzed by mixed model methods. Individuals with sparse flowering presented higher breeding values for total dry matter, yield, and total number of panicles per plant than individuals with early or late flowering. Considering breeding population differences on flowering behavior, on individual narrow sense heritability and on genetic correlations between flowering, agronomic quality and nutritional quality traits have to be considered in intrapopulation breeding and in intrapopulational recurrent selection.

The objective of the present study was to evaluate live weight gain per animal and per area and its relationship with the characteristics of pastures of Brachiaria brizantha cv. Paiaguás and Piatã. A randomized blocks experimental design was used, with two treatments and six replicates. The experimental area was 8.0 ha, divided into twelve paddocks of 0.67 ha. The grazing method used was continuous stocking, with variable stocking rate. Three tester steers were used per paddock. Sward heights were measured once a week, and the stocking rate (SR) was adjusted using regulator steers to maintain the sward height at 30 cm. Pasture samples were collected once a month, and herbage accumulation rate (HAR), percentage of leaves (PL), leaf:stem ratio (LSR), and nutritive value (NV) were determined. Animals were weighed every 28 days. No differences between the two cultivars were observed during the wet season for any of the evaluated parameters. However, cv. Paiaguás presented higher HAR and, consequently, higher SR than cv. Piatã during the dry season. As a result of its higher regrowth, cv. Paiaguás pastures presented significantly higher PL, LSR, and NV and, consequently, significantly higher average daily live weight gain. These differences resulted in higher live weight gain per area for Paiaguás grass (695 kg/ha per year) than for Piatã grass (645 kg/ha per year). Thus, Brachiaria brizantha cv. Paiaguás is a good alternative to decrease the temporary forage shortage and for the diversification of pastures in the Cerrado biome region.

The breeding program Brachiaria developed by Embrapa Beef Cattle provides studies to obtain forage with agronomic characters desired by farmers. In this regard, in 2013 and 2014, a study was carried out in order to select the best Brachiaria decumbens intraspecific hybrids, which are superior in relation to production, forage nutritional value, and resistance to spittlebugs. Estimates of genetic parameters and gains with selection were carried out. It was found that there was significant variability between genotypes for all characters. Gain with selection (GS%) ranged from 12 to 324%, and the highest percentage was found for weight of pure seeds (PS) of seed collectors of the second harvest. For reproductive tillers (RT), C001 and R091 hybrids had better performance than the control, and this character may be considered as a parameter to estimate production of pure seeds before flowering starts. Made available in DSpace on 2018-02-21T00:40:47Z (GMT). No. of bitstreams: 1 18CharacterizationandselectionofinterspecifichybridsofBrachiariadecumbensforseedproductioninCampoGrandeMS2016.pdf: 6901799 bytes, checksum: bcf4259300fecffa79b36a55fae263a1 (MD5) Previous issue date: 2018-02-20

The objective of this work was to estimate genetic parameters for agronomic traits and resistance to spittlebugs in B. decumbens hybrids and to select the ones with best performance. For that, 324 hybrids were evaluated in field plots for agronomic traits and in the greenhouse for resistance to spittlebugs. Genetic variability amongst the hybrids was observed for all traits analyzed. The heritability estimates between genotypes means were higher than 0.52 for all agronomic traits and 0.98 and 0.99 for nymphal survival and nymphal period duration respectively. Hybrids with better performance than cultivar Basilisk for each individual trait were identified and also through a selection index combining all traits. Assigning weights to the different traits in the selection index did not significantly alter the rank for superior hybrids. Those were selected to continue on to the next phases of the breeding program. Resumo O objetivo deste trabalho foi estimar parâmetros genéticos para caracteres agronômicos e de resistência às cigarrinhas-das-pastagens em híbridos de Brachiaria decumbens e selecionar os de melhor desempenho. Trezentos e vinte e quatro híbridos foram avaliados em campo para caracteres agronômicos e em casa de vegetação para resistência às cigarrinhas-das-pastagens. Observou-se existência de variabilidade genética entre os híbridos para todos os caracteres analisados. As estimativas de herdabilidade entre médias de genótipos foram superiores a 0,52 para todos os caracteres agronômicos e de 0,98 para sobrevivência ninfal e 0,99 para duração do período ninfal. Híbridos com melhor desempenho em relação a cultivar Basilisk foram identificados para cada caráter individualmente e conjuntamente por meio de índices de seleção. A atribuição de pesos diferentes entre os caracteres nos índices de seleção não alterou significativamente o ranqueamento dos híbridos. Híbridos superiores foram selecionados para as próximas etapas do programa de melhoramento.

The objective of this research was to select hybrids with better performance in microsporogenesis and with lower percentage of unviable pollen to be used in the forage improvement programs of Embrapa Beef Cattle. The genetic diversity in the genus Brachiaria is restricted and intra- and interspecific crosses are being performed to create variability. Accessions of B. decumbens were crossed and in the F1 generation hybrids that retained seeds in the inflorescence were selected. Cytogenetic evaluations were then performed to identify meiotic abnormalities which could be detrimental to pollen viability and consequently to seed production. For the meiotic studies, young inorescences were collected from twenty seven intraspecific hybrids, xed in a mixture of6 ethanol: 3 chloroform: 2 propionic acid for 24 h and stored under refrigeration. The microsporocytes and the pollen grains were prepared by smear and staining with 1% propionic carmine and analyzed under light microscopy. For each hybrid, 100 cells in each phase of meiosis, between diakinesis and tetrad stages were analyzed. Chromosomal associations were analyzed in diakinesis and the counting of chromosome number in anaphase I. The chromosome behavior was analyzed in from metaphase I until the tetrad stage, and the percentages of irregularities were related to irregular segregation of chromosomes, micronuclei formation, microcytes and polyads. The percentages of abnormal tetrads and unviable pollen were subjected to analysis of variance with the SAS 9.2 software. Later, the Scott Knott test was applied at 5% probability of error with the GENES program. The hybrids are tetraploid (2n=4x=36). The frequency of meiotic abnormalities variedbetween 7% and 100%.Depending on the phases and hybrids, and the behavior of chromosomes during meiosis characterizes asynchrony of genomes.In the final product of meiosis, the main abnormalities identified were micronuclei, microcytesand polyads.The high frequency of irregularities in the segregation of chromosomes affects pollen viability. Fifteen of the 27 hybrids evaluated presented viability below 32%. Of the 27 intraspecific hybrids, the apomictic hybrids R158, R169 and R184 can be kept for the development of new cultivars process and also be used as pollen donors, whereas the most promising sexual hybrids that can be utilized in new crossings as pollen receptors are R161, R163, R165, R167, R181, R193, S47, Y21 and Z9 Objetivou-se,neste trabalho,avaliar os híbridos de Brachiaria decumbens com resistência à degrana natural e selecionar os que apresentaram maior porcentagem de pólen viávele melhor desempenho na microsporogênese, para serem utilizados no programa de melhoramento da Embrapa Gado de Corte. A diversidade genética no gênero Brachiariaé restrita e, portanto,cruzamentos intra e interespecíficos são realizados para gerar variabilidade. Acessos de B. decumbens foram cruzados e, na geração F1,os híbridos resistentes à degrana natural foram selecionados. Avaliações citogenéticas foram realizadas para identificar as anormalidades meióticas que podem interferir na viabilidade do pólen e, conseqüentemente,na produção de sementes. Para os estudos meióticos, inflorescências jovens foram coletadas de 27 híbridos, fixadas em uma solução preparada com6 partes deetanol, 3 partes de clorofórmio e duas partesde ácido propiônico por 24 horas e armazenadas em álcool 70%,sob refrigeração. Os microsporócitos e os grãos de pólen foram preparados utilizando a técnica de esmagamento e coloração com carmim propiônico a 1% e observadas sob microscopia de luz. Para cada híbrido, foram analisadas 100 células em cada fase da meiose, compreendidas entre a diacinese e a tétrade. As associações cromossômicas foram analisadas na diacinese e a contagem do número de cromossomos em anáfase I.O comportamento cromossômico foi analisado em metáfase I até a tétrade.As porcentagens de irregularidades observadas foram relacionadas coma segregação irregular dos cromossomos, formação de micronúcleos, micrócitos e políades.As porcentagens de tétrades anormais e dos grãos de polens inviáveis foram submetidas à análise de variância, utilizando o programa SAS 9.2. Após, foi realizado o teste de Scott Knott, ao nível de 5% de probabilidade, utilizando o programa Genes.Todos os 27 híbridos analisados são tetraploides (2n=4x=36). A frequência de anormalidades na meiose variou de 7% a 100% entre as fases e os híbridos. O comportamento dos cromossomos durante a meiose caracterizou assincronia do genoma. No produto final da meiose, as principais irregularidades encontradas foram micronúcleos, micrócitos e políades. A alta frequência de irregularidades na segregação dos cromossomos afetou a viabilidade do pólen. Quinze dos 27 híbridos avaliados apresentaram viabilidade abaixo de 32%.Entre os 27 híbridos intraespecíficos, os híbridos apomíticos, que podem ser mantidos no processo de desenvolvimento de novas cultivares e também serem utilizados como doadores de pólen,foram R158, R169 e R184.Os híbridos sexuais mais promissores, que podem ser aproveitados em novos cruzamentos como receptores de pólen, foram R161, R163, R165, R167, R181, R193, S47, Y21 e Z9 x, 60 f

The objectives of this study were to detect genetic variability among genotypes of Brachiara humidicola, study the genetic diversity and identify redundant variables in the discrimination of hybrids. Fifteen genotypes were evaluated for morphological, agronomic and nutritive characteristics in a randomized block design with six replications, in Rio Branco, Acre. Analysis of variance was performed, followed by the Scott-Knott test. Different techniques of multivariate analysis were used to study genetic diversity. Significant differences in plant performance were observed for agronomic and morphological characteristics, but not for nutritive value. There was consistency between the different clustering techniques. Four redundant characteristics were identified hat can be discarded. The existence of divergent and superior hybrids that can be used in recurrent selection (sexual) programs or can be released as new (apomictic) cultivars after testing for animal response was confirmed. The lack of genetic variability in bromatological traits indicates the need for differentiated selection strategies.

Brachiaria humidicola is a perennial and stoloniferous forage grass, with excellent adaptation to infertile soils and waterlogging. Producers in northern Brazil have become interested in this species, especially after the degradation of large areas of lowly permeable soils sown with B. brizantha cv. Marandu, which is highly intoler-ant of soil waterlogging (Andrade and Valentim 2006). However, since only 3 cultivars of B. humidicola are registered in Brazil (Mapa 2013), there is a need to de-velop new cultivars adapted to the range of environ-mental conditions experienced. Recently, Embrapa Beef Cattle obtained intraspecific hybrids of B. humidicola that need to be evaluated agronomically, aiming at sub-sequent grazing trials and future releases. The objective of this study was to evaluate and select apomictic and sexual hybrids of B. humidicola under the environmental conditions of the state of Acre, in western Brazilian Amazon. Publicado também nos Anais do 22º INTERNATIONAL GRASSLAND CONGRESS, Sidney, 2013.

Agroforestry systems for animal husbandry, including integrated crop-livestock-forest systems (ICLF) are rather diversified in the five Brazilian regions. They present several technical, environmental and socioeconomic benefits. However they are not broadly adopted, mainly because of their higher complexity compared with traditional systems as well as a certain lack of understanding by farmers regarding their benefits. To change this situation, in the last five years, the Brazilian government has directed financial resources for credit as well as for research and technology transfer addressing ICLF systems, including good agricultural practices and mitigation of greenhouse gases emissions. The goal is to improve competitiveness of the Brazilian agribusiness sector. Publicado também nos Anais do 22º INTERNATIONAL GRASSLAND CONGRESS, Sidney, 2013.

The genus Brachiaria comprises more than 100 species and is the single most important genus of forage grass in the tropics. Brachiaria brizantha, widely used in Brazilian pastures for beef and dairy production, is native to tropical Africa. As a subsidy to the breeding program underway in Brazil, cytological studies were employed to determine the chromosome number and to evaluate microsporogenesis in 46 accessions of this species available at Embrapa Beef Cattle (Brazil). Thirty-four accessions presented 2n = 36; seven had 2n = 45, and five had 2n = 54 chromosomes. Based on the higher level of chromosome association observed in diakinesis, in tetra-, penta-, and hexavalents, respectively, it was concluded that they are derived from x = 9; consequently, these accessions are tetra- (2n = 4x = 36), penta- (2n = 5x = 45), and hexaploids (2n = 6x = 54). The most common meiotic abnormalities were irregular chromosome segregation due to polyploidy. Chromosome stickiness, abnormal cytokinesis, non-congressed bivalents in metaphase I and chromosomes in metaphase II, and chromosome elimination were recorded at varying frequencies in several accessions. The mean percentage of meiotic abnormalities ranged from 0.36 to 95.76%. All the abnormalities had the potential to affect pollen viability by generating unbalanced gametes. Among the accessions, only the tetraploid ones with less than 40% of abnormalities are suitable as pollen donors in intra- and interspecific crosses. Currently, accessions with a high level of ploidy (5 and 6n) cannot be used as male genitors in crosses because of the lack of sexual female genitors with the same levels of ploidy.

A utilização de marcadores moleculares pode servir para direcionar cruzamentos, confirmar novos híbridos e identificar genótipos para fins comerciais. Nesse contexto, o objetivo deste trabalho foi analisar a diversidade genética entre cultivares e híbridos de Brachiaria spp. e Panicum maximum usando marcadores moleculares do tipo RAPD (Polimorfismos de DNA amplificados ao acaso). Foram 22 genótipos analisados com 10 primers, os quais amplificaram 178 fragmentos polimórficos de DNA, que foram usados para estimar a similaridade genética por meio do coeficiente de Jaccard. Os valores de similaridade obtidos variaram de 0,066 a 0,841. A estrutura genética entre todos os genótipos estudados foi estimada pelo método UPGMA (Método de agrupamento com médias aritméticas não ponderadas), revelando três grupos distintos com altos valores de bootstrap (>89%). Os resultados demonstraram que a técnica RAPD oferece uma maneira rápida, relativamente barata e útil para a caracterização da diversidade genética entre as diferentes cultivares e híbridos de Brachiaria ssp. e P. maximum analisados

O objetivo deste trabalho foi descrever o processo de embriogênese somática em Urochloa brizantha cv. Marandu (Syn. Brachiaria brizantha cv. Marandu) e fornecer subsídios para o aprimoramento dos métodos de cultura de tecidos e transformação genética. Calos embriogênicos foram obtidos por indução em embriões isolados de sementes maduras, e cultivados in vitro, em meio de cultura que continha ácido 2,4‑diclorofenoxiacético, 6‑benzilaminopurina e caseína hidrolisada. Plântulas foram regeneradas a partir dos calos embriogênicos, na presença de ácido naftalenoacético e cinetina. Esse processo foi descrito morfologicamente por observações em microscopia de luz de secções seriadas semifinas de tecidos fixados, ao longo do processo de regeneração, em FAA [formaldeído (40%): ácido acético glacial: etanol (50%), a 5:5:90 v/v/v]. Os embriões das sementes de U. brizantha cv. Marandu não têm epiblasto e são classificados como do tipo panicoide. Nas condições estabelecidas de cultura in vitro, calos embriogênicos e embriões somáticos de U. brizantha cv. Marandu, desenvolvem-se a partir de células meristemáticas do escutelo. Made available in DSpace on 2011-07-08T12:17:43Z (GMT). No. of bitstreams: 1 cacilda.pdf: 1784107 bytes, checksum: 18472a2dcdd708da90d4617b46e513a2 (MD5) Previous issue date: 2011-03-30

Polyploidy is a prominent and significant force in plant evolution, taking place since ancient times and continuing until today. Recent cytogenetic studies in the genus Brachiaria using germplasm collected from wild African savannas in the 1980s revealed that most species and accessions within species are polyploid. Diploid, tetraploid, and pentaploid accessions have been found. We found asynchronous meiosis during microsporogenesis, followed by genome elimination, in two pentaploid (2n = 5x = 45) accessions (D53 and D71) of a hardy, invasive pasture grass, introduced from Africa to Brazil, Brachiaria decumbens. In these accessions, chromosomes paired as 18 bivalents and nine univalents during diakinesis, suggesting that these accessions resulted from a recent event of natural hybridization. The lack of chromosome associations in the genomes suggests that these accessions resulted from hybridization between two genotypes that are not closely related, with low genome affinity and with different meiotic rhythms. This supposition is reinforced by the meiotic behavior of the nine univalents, which were always laggard in relation to the other chromosomes and eliminated as micronucleiin microspores. The behavior of these accessions, which have an odd level of ploidy and confirmed genome elimination, supports the general assumption that a polyploid accession can undergo a new event of polyploidization by natural hybridization (neopolyploidyzation). This evidence for natural hybridization in Brachiaria shows that this is a wild genus in an ongoing evolutionary process. Made available in DSpace on 2018-01-29T23:35:39Z (GMT). No. of bitstreams: 1 Genomeeliminationduringmicrosporogenesis.pdf: 721536 bytes, checksum: 67b43404b72d431e529e650092e6e97f (MD5) Previous issue date: 2011-03-30

Brachiaria humidicola (Poaceae), originally from Africa, is an economically important pasture plant in tropical South America. An accession of B. humidicola (H038) collected from the wild African savanna (Mbeya, Tanzania) showed irregular microsporogenesis. This meiotic behavior was consistent with an allopolyploid origin. Multivalent chromosome association at diakinesis gave tri- to octavalents, associated with two nucleoli in some cells. Six non-congregated univalents in metaphase I and anaphase I, along with previous lines of evidence for x = 6 in B. humidicola, confirm H038 as a nonaploid accession, 2n = 9x = 54. Asynchrony in the genome during microsporogenesis also corroborated this assumption. Its putative origin could be a cross between two related species with different rhythms in meiosis. The meiotic behavior of this accession reinforces the hypothesis of the existence of a new basic chromosome number (x = 6) for Brachiaria. The use of this accession in the breeding of this important forage grass for the tropics is discussed. Made available in DSpace on 2018-01-29T23:35:17Z (GMT). No. of bitstreams: 1 Meioticbehaviorofanonaploid.pdf: 482740 bytes, checksum: e7a8a1f2cef909835c028b711caa0236 (MD5) Previous issue date: 2010-03-19

Microsporogenesis in an interspecific Brachiaria hybrid, grown in the field under natural environmental conditions in Brazilian savannas, was analyzed in three distinct years of collection. Several types of meiotic abnormalities were recorded during those three years, but varied in type and frequency depending on the year. The average temperature and rainfall 15 days before collection was unusually high in those years. The percentage of abnormal meiocytes recorded was 62% in 2001, 73% in 2004, and 77% in 2005. The abnormalities observed during microsporogenesis compromised pollen viability by generating unbalanced gametes or affecting nucleolus organization. The environmental conditions under which the hybrid was growing could have affected the genetic control of meiosis. More detailed studies, under controlled conditions, are necessary to better understand the effects of environmental factors on Brachiaria microsporogenesis hybrids. Made available in DSpace on 2011-10-01T01:00:07Z (GMT). No. of bitstreams: 1 gmr430.pdf: 1027729 bytes, checksum: 85fbaccfaac01010c64feadf8ea800fe (MD5) Previous issue date: 2009-04-20

Several mutations are known to alter the normal progression of meiosis and can be correlated with defects in microtubule distribution. The dv mutation affects the spindle organization and chromosomes do not converge into focused poles. Two Brachiaria hybrids presented the phenotypic expressions of dv mutation but exhibited many more details in the second division. Bivalents were distantly positioned and spread over a large metaphase plate and failed to converge into focused poles. Depending on the distance of chromosomes at the poles, telophase I nuclei were elongated or the chromosomes were grouped into various micronuclei of different sizes in each cell. The first cytokinesis occurred. However, when there were micronuclei, a second cytokinesis immediately took place dividing the prophase II meiocytes into three or four cells. In each meiocyte, meiosis progressed to the second division. Slightly elongated nuclei or micronuclei were recorded in telophase II. After a third cytokinesis, hexads or octads were formed. Pollen grains of different sizes were generated. One of these hybrids presented a higher frequency of abnormal cells than when previously analyzed. The fate of these hybrids as genitors or as candidates for cultivars in the Brachiaria breeding program is discussed. Made available in DSpace on 2011-08-02T01:01:28Z (GMT). No. of bitstreams: 1 sdarticle.pdf: 347177 bytes, checksum: d6447873f712c6de4f9843940fa96e11 (MD5) Previous issue date: 2009-04-02

Three accessions of Brachiaria brizantha, three of B. humidicola, and two interspecific hybrids between B. ruziziensis and B. brizantha were analyzed with regard to their mitotic behavior in root tips. All these genotypes revealed chromosome elimination or lack of chromosome affinity in previous analyses of microsporogenesis. Analyses of root tips showed a normal mitotic division in all accessions and hybrids, reinforcing the notion that the genetic control of meiosis is totally independent of that of mitosis. The implications of these findings for the Brachiaria breeding program are discussed. Made available in DSpace on 2012-04-05T01:00:36Z (GMT). No. of bitstreams: 1 Mitoticbehavior.pdf: 497407 bytes, checksum: 05ca133feb990233ce16aef1d3e88fc8 (MD5) Previous issue date: 2008-07-30

Morphological changes have been investigated during plant programmed cell death (PCD) in the last few years due to the new interest in a possible apoptotic-like phenomenon existing in plants. Although PCD has been reported in several tissues and specialized cells in plants, there have been few reports of its occurrence during microsporogenesis. The present study reports a typical process of PCD during meiosis in an interspecific Brachiaria hybrid leading to male sterility. In this hybrid, some inflorescences initiated meiosis but it was arrested in zygotene/pachytene. From this stage, meiocytes underwent a severe alteration in shape showing substantial membrane blebbing; the cytoplasm became denser at the periphery; the cell nucleus entered a progressive stage of chromatin disintegration, and then the nucleolus disintegrated, and the cytoplasm condensed and shrunk. The oldest flowers of the raceme showed only the callose wall in the anthers showing obvious signs of complete sterility. Made available in DSpace on 2018-01-29T23:34:19Z (GMT). No. of bitstreams: 1 Evidenceofprogrammedcell.pdf: 666968 bytes, checksum: e913e6f0092ee2cdfafea4fd787c7aee (MD5) Previous issue date: 2008-03-17

Made available in DSpace on 2017-04-20T23:50:36Z (GMT). No. of bitstreams: 1 capimpiata.pdf: 1015297 bytes, checksum: 70d2d57a3f22489f728cdc45ad800e38 (MD5) Previous issue date: 2013-10-29

Microsporogenesis of several Brachiaria species of the Brazilian collection at Embrapa Beef Cattle has been analyzed in detail. This paper reports abnormal cytokinesis in three accessions of three different species (Brachiaria humidicola, 2n = 4x = 36, Brachiaria decumbens, 2n = 4x = 36, and Brachiaria dura, 2n = 6x = 54). Chromosomes paired in bi-, tri-, and quadrivalents in these accessions, whereas chromosome segregation at meiosis I was characterized by exclusion of laggards as micronuclei. In a high number of meiocytes, the first sign of cytokinesis appeared only in metaphase II and did not divide the meiocyte into a dyad. Total absence of cytokinesis was also detected among meiocytes in the second division. Since in both cases the two metaphase plates were very close, they favored the rejoining of chromosome sets after anaphase II and formed a restitutional nucleus in telophase II. Second cytokinesis occurred after telophase II in most meiocytes. Monads, dyads, and triads with n or 2n nuclei were observed among meiotic products. The 2n gametes observed correspond to the first division restitution (FDR). The number of affected cells in each accession was variable, but the number of microspores with restitutional nucleus, including those scored in tetrads and the released ones, did not exceed 9%. Although polyploidy is common in the genus Brachiaria, its origin is still unclear. Current results suggest that 2n gametes may have contributed to the evolutionary history of the genus. Made available in DSpace on 2011-07-22T01:04:31Z (GMT). No. of bitstreams: 1 fulltext.pdf: 497735 bytes, checksum: 7fb01baf73bf5ad563901582465040ec (MD5) Previous issue date: 2008-02-01 CNPGC.

Background Urochloa humidicola is a forage grass that grows in tropical regions and is recognized for its tolerance to seasonal flooding. It is a polyploid and apomictic species with high phenotypic plasticity. As molecular tools are important in facilitating the development of new cultivars and in the classification of related species, the objectives of this study were to develop new polymorphic microsatellite markers from an enriched library constructed from U. humidicola and to evaluate their transferability to other Urochloa species. Findings Microsatellite sequences were identified from a previously constructed enriched library, and specific primers were designed for 40 loci. Isolated di-nucleotide repeat motifs were the most abundant followed by tetra-nucleotide repeats. Of the tested loci, 38 displayed polymorphism when screened across 34 polyploid Urochloa sp. genotypes, including 20 accessions and six hybrids of U. humidicola and two accessions each from U. brizantha, U. dictyoneura, U. decumbens and U. ruziziensis. The number of bands per Simple Sequence Repeat (SSR) locus ranged from one to 29 with a mean of 11.5 bands per locus. The mean Polymorphism Information Content (PIC) of all loci was 0.7136, and the mean Discrimination Power (DP) was 0.7873. Six loci amplified in all species tested. STRUCTURE analysis revealed six different allelic pools, and the genetic similarity values analyzed using Jaccard's coefficient ranged from 0.000 to 0.913. Conclusions This work reports new polymorphic microsatellite markers that will be useful for breeding programs for Urochloa humidicola and other Urochloa species as well as for genetic map development, germplasm characterization, evolutionary and taxonomic studies and marker-assisted trait selection.