Toward in vitro fertilization in Brachiaria spp.

Brachiaria are forage grasses widely cultivated in tropical areas. In vitro pollination was applied to accessions of Brachiaria spp. by placing pollen of non-dehiscent anthers on a solid medium near isolated ovaries. Viability and in vitro germination were tested in order to establish good conditions for pollen development. Comparing sexual to apomictic plants, apomictic pollen has more abortion after meiosis during the microspore stage and a lower viability and, of both types, only some plants have sufficient germination in a high sugar concentration. Using in vitro pollination with the sexual plant, the pollen tube penetrates into the nucellus and micropyle, but the embryo sac degenerates and collapses. In the apomictic B. decumbens, in vitro pollination leads to the transfer of the sperm nuclei into the egg cell and the central cell. The results are discussed according to normal fertilization and barriers in sexual and apomictic plants

Viroses da batata-doce no Brasil: importância e principais medidas de controle.

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Viroses do alho no Brasil: importância e principais medidas de controle

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Biossegurança no desenvolvimento e uso das plantas transgênicas.

A produção agrícola está sob constante pressão de ataque de pragas comprometendo a produtividade. Entre as ferramentas de combate está a obtenção de variedades resistentes e a utilização de plantas geneticamente modificadas (PGM). Entretanto, para estas últimas são levantadas questões sobre os riscos para o meio ambiente e o homem. Para responder a estas questões e normatizar o processo de avaliação e aprovação de PGM foram criados dispositivos legais na forma de regulamentações nacionais e internacionais. Visando o desenvolvimento de análise de riscos, em nível nacional, e o atendimento à legislação vigente, foi estruturada uma Rede de Pesquisa pela Embrapa - a BioSeg. Ela estuda os riscos ambiental e alimentar de: ALGODÃO (resistente a insetos), BATATA (resistente ao virus Y), FEIJÃO (resistente ao virus do mosaico dourado), MAMÃO (resistente ao vírus da mancha anelar), SOJA (tolerante ao glifosato). A vivência de 4 anos de trabalho desta Rede será apresentada, com ênfase nos resultados alcançados e perspectivas futuras. Financiamento: Embrapa (0102201) e Finep (01020162-00). Parceria com Projeto GMO ERA (recursos - SDC/Suíça)

In situ localization of three cDNA sequences associated with the later stages of aposporic embryo sac development of Brachiaria brizantha.

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Energy Relaxation in Nonlinear One-Dimensional Lattices

We study energy relaxation in thermalized one-dimensional nonlinear arrays of the Fermi-Pasta-Ulam type. The ends of the thermalized systems are placed in contact with a zero-temperature reservoir via damping forces. Harmonic arrays relax by sequential phonon decay into the cold reservoir, the lower frequency modes relaxing first. The relaxation pathway for purely anharmonic arrays involves the degradation of higher-energy nonlinear modes into lower energy ones. The lowest energy modes are absorbed by the cold reservoir, but a small amount of energy is persistently left behind in the array in the form of almost stationary low-frequency localized modes. Arrays with interactions that contain both a harmonic and an anharmonic contribution exhibit behavior that involves the interplay of phonon modes and breather modes. At long times relaxation is extremely slow due to the spontaneous appearance and persistence of energetic high-frequency stationary breathers. Breather behavior is further ascertained by explicitly injecting a localized excitation into the thermalized array and observing the relaxation behavior

Viral reinfection affecting bulb production in garlic after seven years of cultivation under field conditions.

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Viral reinfection affecting bulb production in garlic after seven years of cultivation under field conditions.

Made available in DSpace on 2018-06-06T01:01:27Z (GMT). No. of bitstreams: 1 ID278821.pdf: 230271 bytes, checksum: f03196838e7a796b2c3aacb0c8b5ca6a (MD5) Previous issue date: 2007-01-16bitstream/item/178115/1/ID-27882-1.pd