This paper analyses the present status of tropical forage resources and their utilization in the ... more This paper analyses the present status of tropical forage resources and their utilization in the development of novel cultivars based on the accumulated information from past decades of collecting, evaluation and whatever little breeding has been pursued. The situation of world collections of tropical forages is presented and discussed in the light of limited investment and dwindling resources. A cause for concern is the lesser priority assigned to conservation and manipulation of official tropical germplasm banks, such as CSIRO’S and CIAT’s. In order to assure the availability of tropical genetic resources for the future it is imperative that international efforts be undertaken to renew investments into organizing world databases, providing human and financial resources to maintain existing collections and that national and international research organizations be stimulated to act cooperatively in favor of a common goal. Perhaps by assigning value to biodiversity, the stimuli for n...
Two strategies have been used in the breeding of Brachiaria (syn. Urochloa) to produce new cultiv... more Two strategies have been used in the breeding of Brachiaria (syn. Urochloa) to produce new cultivars. The first involves exploring the natural variability existing in nature, which is the selection of ecotypes, mostly apomicts, from the diversity in germplasm banks. This strategy proved efficient originally and the cultivars in use in Brazil were derived in this way, but progress with this strategy is limited in the medium to long term
The genus Urochloa P. Beauv. [syn. Brachiaria (Trin.) Griseb.] comprises species of great economi... more The genus Urochloa P. Beauv. [syn. Brachiaria (Trin.) Griseb.] comprises species of great economic relevance as forages. The genomic constitution for the allotetraploid species Urochloa brizantha (cv. Marandu) and Urochloa decumbens (cv. Basilisk) and the diploid Urochloa ruziziensis was previously proposed as BBB 1 B 1 , B 1 B 1 B 2 B 2 and B 2 B 2 , respectively. Evidence indicates U. ruziziensis as the ancestral donor of genome B 2 in U. decumbens allotetraploidy, but the origin of the genomes B and B 1 is still unknown. There are diploid genotypes of U. brizantha and U. decumbens that may be potential ancestors of the tetraploids. The aim of this study was to determine the genomic constitution and relationships between genotypes of U. brizantha (2x and 4x), U. decumbens (2x and 4x) and U. ruziziensis (2x) via genomic in situ hybridization (GISH). Additionally, chromosome number and genome size were verified for the diploid genotypes. The diploids U. brizantha and U. decumbens presented 2n = 2x = 18 chromosomes and DNA content of 1.79 and 1.44 pg, respectively. The GISH analysis revealed high homology between the diploids U. brizantha and U. decumbens, which suggests relatively short divergence time. The GISH using genomic probes from the diploid accessions on the tetraploid accessions' chromosomes presented similar patterns, highlighting the genome B 1 present in both of the tetraploids. Based on GISH results, the genomic constitution was proposed for the diploid genotypes of U. brizantha (B 1 B 1) and U. decumbens (B 1 ′B 1 ′) and both were pointed as donors of genome B 1 (or B 1 ′), present in the allotetraploid genotypes.
The autotetraploid forage Congo signal grass (Brachiaria ruziziensis) is an important component i... more 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 Q ST 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.
The African species Urochloa humidicola (Rendle) Morrone & Zuloaga (syn. Brachiaria humidicola (R... more 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 ...
Forage grasses of the African genus Urochloa (syn. Brachiaria) are the basis of Brazilian beef pr... more 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. 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 micr...
Brazil has the largest commercial beef cattle herd and is the main beef exporter in the world. Cu... more 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 are of apomictic reproduction, thus genetically homogeneous. Tropical 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.
two with and two without fertilization. Details of soil characteristics, applied fertilizer, expe... more two with and two without fertilization. Details of soil characteristics, applied fertilizer, experimental design and evaluation procedures were described earlier (Jank and Savidan, 1984 ; Savidan et al., 1985). This paper will report results for the main variables measured, which were : leaf dry matter yield
O objetivo deste trabalho foi avaliar o desempenho agronômico de genótipos de capim-braquiária [U... more O objetivo deste trabalho foi avaliar o desempenho agronômico de genótipos de capim-braquiária [Urochloa brizantha (Syn. Brachiaria brizantha)] em sucessão à soja, para uso em sistemas de integração lavoura-pecuária. Os genótipos Marandu, MG 4, Xaraés, Piatã, Arapoty e B 6, foram avaliados na safrinha, durante a estação seca, e a soja na safra de verão, em esquema de sucessão, de 2007 a 2010. Em cada ano, as forrageiras foram semeadas em março, avaliadas em cortes sucessivos até o final de setembro e dessecadas em outubro para a realização do plantio direto da soja em novembro. Utilizou-se o delineamento de blocos ao acaso, com quatro repetições. Xaraés e B 6 estiveram entre os genótipos com maior produção de forragem. A cultivar Xaraés apresentou menores teores de proteína bruta, digestibilidade in vitro da matéria orgânica, cálcio e fósforo, embora esses teores possam ser considerados bons para o gênero, uma vez que o solo de cultivo apresentava boa fertilidade. Há variação entre ...
Among 25 accessions of Brachiaria brizantha in the Embrapa Beef Cattle collection, one accession ... more Among 25 accessions of Brachiaria brizantha in the Embrapa Beef Cattle collection, one accession (GC 1113/95) presented a severe case of chromosome stickiness in meiosis, impairing normal chromosome segregation. Accession was tetraploid (2n =4x=36) with chromosomes pairing in bivalents and few quadrivalents at diakinesis. Stages of prophase I were normal and chromosome stickiness became evident from metaphase I persisting to microspore stage. Bridges of different thickness were formed in anaphase I and II by chromosomes that did not separate. Some of them even persisted until telophase stages. The precise causes of chromosome stickiness could not be ascertained, but genetic factors might be controlling the phenomenon, since only this accession cultivated on Brazilian savannas under the same environmental conditions of the 24 other accessions presented the abnormality.
The objectives of this study were to detect genetic variability among genotypes of Brachiara humi... more 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 that 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. T...
This paper analyses the present status of tropical forage resources and their utilization in the ... more This paper analyses the present status of tropical forage resources and their utilization in the development of novel cultivars based on the accumulated information from past decades of collecting, evaluation and whatever little breeding has been pursued. The situation of world collections of tropical forages is presented and discussed in the light of limited investment and dwindling resources. A cause for concern is the lesser priority assigned to conservation and manipulation of official tropical germplasm banks, such as CSIRO’S and CIAT’s. In order to assure the availability of tropical genetic resources for the future it is imperative that international efforts be undertaken to renew investments into organizing world databases, providing human and financial resources to maintain existing collections and that national and international research organizations be stimulated to act cooperatively in favor of a common goal. Perhaps by assigning value to biodiversity, the stimuli for n...
Two strategies have been used in the breeding of Brachiaria (syn. Urochloa) to produce new cultiv... more Two strategies have been used in the breeding of Brachiaria (syn. Urochloa) to produce new cultivars. The first involves exploring the natural variability existing in nature, which is the selection of ecotypes, mostly apomicts, from the diversity in germplasm banks. This strategy proved efficient originally and the cultivars in use in Brazil were derived in this way, but progress with this strategy is limited in the medium to long term
The genus Urochloa P. Beauv. [syn. Brachiaria (Trin.) Griseb.] comprises species of great economi... more The genus Urochloa P. Beauv. [syn. Brachiaria (Trin.) Griseb.] comprises species of great economic relevance as forages. The genomic constitution for the allotetraploid species Urochloa brizantha (cv. Marandu) and Urochloa decumbens (cv. Basilisk) and the diploid Urochloa ruziziensis was previously proposed as BBB 1 B 1 , B 1 B 1 B 2 B 2 and B 2 B 2 , respectively. Evidence indicates U. ruziziensis as the ancestral donor of genome B 2 in U. decumbens allotetraploidy, but the origin of the genomes B and B 1 is still unknown. There are diploid genotypes of U. brizantha and U. decumbens that may be potential ancestors of the tetraploids. The aim of this study was to determine the genomic constitution and relationships between genotypes of U. brizantha (2x and 4x), U. decumbens (2x and 4x) and U. ruziziensis (2x) via genomic in situ hybridization (GISH). Additionally, chromosome number and genome size were verified for the diploid genotypes. The diploids U. brizantha and U. decumbens presented 2n = 2x = 18 chromosomes and DNA content of 1.79 and 1.44 pg, respectively. The GISH analysis revealed high homology between the diploids U. brizantha and U. decumbens, which suggests relatively short divergence time. The GISH using genomic probes from the diploid accessions on the tetraploid accessions' chromosomes presented similar patterns, highlighting the genome B 1 present in both of the tetraploids. Based on GISH results, the genomic constitution was proposed for the diploid genotypes of U. brizantha (B 1 B 1) and U. decumbens (B 1 ′B 1 ′) and both were pointed as donors of genome B 1 (or B 1 ′), present in the allotetraploid genotypes.
The autotetraploid forage Congo signal grass (Brachiaria ruziziensis) is an important component i... more 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 Q ST 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.
The African species Urochloa humidicola (Rendle) Morrone & Zuloaga (syn. Brachiaria humidicola (R... more 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 ...
Forage grasses of the African genus Urochloa (syn. Brachiaria) are the basis of Brazilian beef pr... more 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. 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 micr...
Brazil has the largest commercial beef cattle herd and is the main beef exporter in the world. Cu... more 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 are of apomictic reproduction, thus genetically homogeneous. Tropical 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.
two with and two without fertilization. Details of soil characteristics, applied fertilizer, expe... more two with and two without fertilization. Details of soil characteristics, applied fertilizer, experimental design and evaluation procedures were described earlier (Jank and Savidan, 1984 ; Savidan et al., 1985). This paper will report results for the main variables measured, which were : leaf dry matter yield
O objetivo deste trabalho foi avaliar o desempenho agronômico de genótipos de capim-braquiária [U... more O objetivo deste trabalho foi avaliar o desempenho agronômico de genótipos de capim-braquiária [Urochloa brizantha (Syn. Brachiaria brizantha)] em sucessão à soja, para uso em sistemas de integração lavoura-pecuária. Os genótipos Marandu, MG 4, Xaraés, Piatã, Arapoty e B 6, foram avaliados na safrinha, durante a estação seca, e a soja na safra de verão, em esquema de sucessão, de 2007 a 2010. Em cada ano, as forrageiras foram semeadas em março, avaliadas em cortes sucessivos até o final de setembro e dessecadas em outubro para a realização do plantio direto da soja em novembro. Utilizou-se o delineamento de blocos ao acaso, com quatro repetições. Xaraés e B 6 estiveram entre os genótipos com maior produção de forragem. A cultivar Xaraés apresentou menores teores de proteína bruta, digestibilidade in vitro da matéria orgânica, cálcio e fósforo, embora esses teores possam ser considerados bons para o gênero, uma vez que o solo de cultivo apresentava boa fertilidade. Há variação entre ...
Among 25 accessions of Brachiaria brizantha in the Embrapa Beef Cattle collection, one accession ... more Among 25 accessions of Brachiaria brizantha in the Embrapa Beef Cattle collection, one accession (GC 1113/95) presented a severe case of chromosome stickiness in meiosis, impairing normal chromosome segregation. Accession was tetraploid (2n =4x=36) with chromosomes pairing in bivalents and few quadrivalents at diakinesis. Stages of prophase I were normal and chromosome stickiness became evident from metaphase I persisting to microspore stage. Bridges of different thickness were formed in anaphase I and II by chromosomes that did not separate. Some of them even persisted until telophase stages. The precise causes of chromosome stickiness could not be ascertained, but genetic factors might be controlling the phenomenon, since only this accession cultivated on Brazilian savannas under the same environmental conditions of the 24 other accessions presented the abnormality.
The objectives of this study were to detect genetic variability among genotypes of Brachiara humi... more 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 that 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. T...
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