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Search Results: 1 - 10 of 16481 matches for " Cacilda Borges do; "
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Meiotic analysis in induced tetraploids of Brachiaria decumbens Stapf
Simioni, Carine;Valle, Cacilda Borges do;
Crop Breeding and Applied Biotechnology , 2011, DOI: 10.1590/S1984-70332011000100006
Abstract: the meiotic behavior of three tetraploid plants (2n=4x=36) originated from somatic chromosome duplication of sexually reproducing diploid plants of brachiaria decumbens was evaluated. all the analyzed plants presented abnormalities related to polyploidy, such as irregular chromosome segregation, leading to precocious chromosome migration to the poles and micronuclei during both meiotic divisions. however, the abnormalities observed did not compromise the meiotic products which were characterized by regular tetrads and satisfactory pollen fertility varying from 61.36 to 64.86%. chromosomes paired mostly as bivalents in diakinesis but univalents to tetravalents were also observed. these studies contributed to the choice of compatible fertile sexual genitors to be crossed to natural tetraploid apomicts in the b. decumbens by identifying abnormalities and verifying pollen fertility. intraespecific crosses should reduce sterility in the hybrids produced in the breeding program of brachiaria, a problem observed with the interspecific hybrids produced so far.
Meiotic analysis in induced tetraploids of Brachiaria decumbens Stapf
Carine Simioni,Cacilda Borges do Valle
Crop Breeding and Applied Biotechnology , 2011,
Abstract: The meiotic behavior of three tetraploid plants (2n=4x=36) originated from somatic chromosome duplication ofsexually reproducing diploid plants of Brachiaria decumbens was evaluated. All the analyzed plants presented abnormalities relatedto polyploidy, such as irregular chromosome segregation, leading to precocious chromosome migration to the poles and micronucleiduring both meiotic divisions. However, the abnormalities observed did not compromise the meiotic products which were characterizedby regular tetrads and satisfactory pollen fertility varying from 61.36 to 64.86%. Chromosomes paired mostly as bivalents indiakinesis but univalents to tetravalents were also observed. These studies contributed to the choice of compatible fertile sexualgenitors to be crossed to natural tetraploid apomicts in the B. decumbens by identifying abnormalities and verifying pollen fertility.Intraespecific crosses should reduce sterility in the hybrids produced in the breeding program of Brachiaria, a problem observedwith the interspecific hybrids produced so far.
Chromosome duplication in Brachiaria (A. Rich.) Stapf allows intraspecific crosses
Carine Simioni,Cacilda Borges do Valle
Crop Breeding and Applied Biotechnology , 2009,
Abstract: Brachiaria decumbens cv. Basilisk is the single most important forage grass used for pastures in the tropics.Breeding to produce improved cultivars has been impossible until now due to the lack of compatible sexual ecotypes. Thispaper reports the success of somatic chromosome duplication of sexually reproducing diploid plants of B. decumbens and ofa diploid hybrid between B. decumbens and B. brizantha, which should allow intraspecific crosses with natural apomictictetraploid accessions of either species. Polyploidization was induced in explants cultured in vitro on a medium supplementedwith colchicine at 0.01% for 48 hours, transferred to the same medium without colchicine until shoot regeneration occurred.Five sexual tetraploid plants (3.9% of plants recovered) were obtained. Crosses with apomictic cultivars recovered 14 seeds.The novel sexual tetraploids generated were unique and represented a major breakthrough in breeding B. decumbens toobtain superior hybrids.
Microsporogenesis in tetraploid accessions of Brachiaria nigropedata (Ficalho & Hiern) Stapf (Gramineae)
Sayuri Utsunomiya,Karina; Suely Paglirini,Maria; Borges do Valle,Cacilda;
Biocell , 2005,
Abstract: the genus brachiaria (trin.) griseb. has achieved considerable importance to cattle production systems, as a result of the good production and adaptation of a few cultivars to poor and acid soils of the brazilian savannas. many of its species and accessions are polyploid and apomictic, which limits direct hybridization. to assist the breeding program, cytogenetic characterization has been undertaken on the accessions of brachiaria collection at the embrapa beef cattle research center. in this study, chromosome number and meiotic behavior are reported for the brachiaria nigropedata (ficalho & hiern) stapf collection. the 20 available accessions are tetraploid (2n = 4x = 36). chromosomes paired preferentially as bivalents, but quadrivalents were found in high frequencies in some cells. meiotic behavior was, in general, irregular, and varied among accessions. most accessions presented more than 20% of abnormal tetrads. the most common meiotic abnormalities were those related to irregular chromosome segregation due to polyploidy, leading to micronuclei formation in the tetrad stage. a low frequency of other meiotic abnormalities such as the absence of cytokinesis, chromosome stickiness, cell fusion, anaphase bridges, and chromosome transfer among microsporocytes were also recorded in some accessions. limitations of these accessions for use in hybridization programs are discussed.
Desempenho agron?mico de genótipos de capim-braquiária em sucess?o à soja
Machado, Luís Armando Zago;Valle, Cacilda Borges do;
Pesquisa Agropecuária Brasileira , 2011, DOI: 10.1590/S0100-204X2011001100006
Abstract: the objective of this work was to evaluate the agronomic performance of palisade grass genotypes [urochloa brizantha (syn. brachiaria brizantha)] in succession to soybean, for use on crop-livestock integration systems. the marandu, mg 4, xaraés, piat?, arapoty e b 6 genotypes were evaluated as a second crop, during the dry season, and soybean, in the summer crop, in a succession scheme, from 2007 to 2010. in each year, forages were sown in march and evaluated at successive cuts until late september, then desiccated in october to allow for no-tillage soybean seeding in november. a randomized complete block design with four replicates was used. xaraés and b 6 genotypes were among those with higher forage production. the xaraés cultivar showed lower contents of crude protein, in vitro digestibility of organic matter, calcium, and phosphorus, which, however, can be considered good for this genus, since it was grown in fertile soil. there is variation among u. brizantha genotypes as to their performance in the second crop. the xaraés and b 6 genotypes show better performance in succession to soybean, in integrated production systems. the mg 4 and b 6 genotypes are easily desiccated with glyphosate herbicide. soybean yield is not significantly affected by the cultivation in succession to the u. brizantha genotypes.
Meiotic behavior of interspecific hybrids between artificially tetraploidized sexual Brachiaria ruziziensis and tetraploid apomictic B. brizantha (Poaceae)
Felismino, Mariana Ferrari;Pagliarini, Maria Suely;Valle, Cacilda Borges do;
Scientia Agricola , 2010, DOI: 10.1590/S0103-90162010000200010
Abstract: the meiotic behavior of four interspecific promising hybrids was evaluated by conventional cytological methods. the female genitors were two artificially tetraploidized sexual accessions of b. ruziziensis (r41 and r44, 2n = 4χ = 36), which were crossed to an agronomically superior natural tetraploid apomictic genotype of b. brizantha (b140 - bra003395). three of them (hbgc313, hbgc 315, and hbgc324) were sexual and one (hbgc325) apomictic. analyses of some cells in diakinesis revealed multivalent chromosome configurations, suggesting that genetic recombination and introgression of some genes could be present. the four hybrids had different types of meiotic abnormalities at various frequencies. abnormalities related to irregular chromosome segregation due to polyploidy were common among these hybrids, and characterized by precocious chromosome migration to the poles, laggard chromosomes, both generating micronuclei in telophases and tetrads and, as a consequence, unbalanced gametes. one abnormality genotype-specific, related to spindle orientation (a putative divergent spindle mutation), was recorded for the first time in two of the hybrids, hbgc313 and hbgc325. the sexual hybrid hbgc324 had the lower rate of abnormalities, and it could be used as a female genitor in future crosses in the breeding program. the abnormalities present in these hybrids may impact fertility and affect seed production. based on the results, hbgc324 is the single hybrid recommended to the breeding program. hybrids must produce a good amount of viable seeds, besides good overall dry matter production and nutritive value, in order to be widely utilized and adopted in production systems. due to pseudogamy, the desirable superior apomictic hybrids need viable pollen grains to fertilize the secondary nucleus of the embryo sac and thus ensure normal and vigorous endosperm development and plenty of seed set.
Microsporogenesis in tetraploid accessions of Brachiaria nigropedata (Ficalho & Hiern) Stapf (Gramineae)
Karina Sayuri Utsunomiya,Maria Suely Paglirini,Cacilda Borges do Valle
Biocell , 2005,
Abstract: The genus Brachiaria (Trin.) Griseb. has achieved considerable importance to cattle production systems, as a result of the good production and adaptation of a few cultivars to poor and acid soils of the Brazilian savannas. Many of its species and accessions are polyploid and apomictic, which limits direct hybridization. To assist the breeding program, cytogenetic characterization has been undertaken on the accessions of Brachiaria collection at the Embrapa Beef Cattle Research Center. In this study, chromosome number and meiotic behavior are reported for the Brachiaria nigropedata (Ficalho & Hiern) Stapf collection. The 20 available accessions are tetraploid (2n = 4x = 36). Chromosomes paired preferentially as bivalents, but quadrivalents were found in high frequencies in some cells. Meiotic behavior was, in general, irregular, and varied among accessions. Most accessions presented more than 20% of abnormal tetrads. The most common meiotic abnormalities were those related to irregular chromosome segregation due to polyploidy, leading to micronuclei formation in the tetrad stage. A low frequency of other meiotic abnormalities such as the absence of cytokinesis, chromosome stickiness, cell fusion, anaphase bridges, and chromosome transfer among microsporocytes were also recorded in some accessions. Limitations of these accessions for use in hybridization programs are discussed.
Abnormal spindle orientation during microsporogenesis in an interspecific Brachiaria (Gramineae) hybrid
Mendes-Bonato, Andréa Beatriz;Pagliarini, Maria Suely;Valle, Cacilda Borges do;
Genetics and Molecular Biology , 2006, DOI: 10.1590/S1415-47572006000100023
Abstract: this paper reports a case of abnormal spindle orientation during microsporogenesis in an interspecific hybrid of the tropical grass brachiaria. in the affected plant, prophase i was normal. in metaphase i, bivalents were regularly co-oriented but distantly positioned and spread over the equatorial plate. in anaphase i, chromosomes failed to converge into focused poles due to parallel spindle fibers. as a consequence, in telophase i, an elongated nucleus or several micronuclei were observed in each pole. in the second division, the behavior was the same, leading to polyads with several micronuclei. a total of 40% of meiotic products were affected. the use of this hybrid in production systems needing good-quality seeds is discussed.
Chromosome number and microsporogenesis of two accessions of Brachiaria dura Stapf (Poaceae)
Risso-Pascotto, Claudiceia;Pagliarini, Maria Suely;Valle, Cacilda Borges do;
Biota Neotropica , 2009, DOI: 10.1590/S1676-06032009000200024
Abstract: the two accessions of b. dura analyzed (du01 and du02) are hexaploid (2n = 6x = 54), derived from x = 9. meiotic abnormalities, such as precocious chromosome migration to the poles, laggards and micronuclei, were recorded in low frequency in both accessions. the few multivalent chromosome association at diakinesis and meiotic stability suggested that hexaploidy probably resulted from chromosome doubling. in du02, chromosome transfer (cytomixis) among meiocytes, involving part or the entire genome was observed. the implication of these findings for the brachiaria breeding is discussed.
Meiotic arrest compromises pollen fertility in an interspecific hybrid between Brachiaria ruziziensis x Brachiaria decumbens (Poaceae: paniceae)
Mendes-Bonato, Andréa Beatriz;Pagliarini, Maria Suely;Valle, Cacilda Borges do;
Brazilian Archives of Biology and Technology , 2007, DOI: 10.1590/S1516-89132007000500011
Abstract: microsporogenesis was analyzed in an interspecific hybrid between an artificially tetraploidized sexual accession of brachiaria ruziziensis (2n=4x=36) and a natural apomictic tetraploid accession of b. decumbens. syncytes involving a large number of cells were recorded in 15.4% of meiocytes. meiosis progressed normally in syncytes during prophase i; in metaphase i, however, several nuclei were found fusioned, showing chromosome stickiness and several chromosome fragments. meiosis was arrested in metaphase i and pycnotic nuclei and micronuclei were formed. abnormal cytokinesis fractionated the syncyte into abnormal meiotic products that were covered by the pollen wall. meiocytes in leptotene were recorded in all the slides prepared for both meiotic divisions, and abnormal "pollen grains" with well-developed pollen wall but containing leptotene nuclei were recorded in 9.18% of grains analyzed. these findings suggested that the meiocytes received the signal to enter meiosis but lacked the signal to proceed beyond leptotene. despite the absence of the meiotic process, such cells were covered by pollen grain wall. total pollen sterility resulted from these abnormalities combined with still others observed among meiocytes.
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