Meiotic Stability, Chloroplast DNA Polymorphisms, and Morphological Traits of Upland X Lowland Switchgrass Reciprocal Hybrids

Switchgrass (Panicum virgatum L.) has two cytotypes or cytoplasm types, L and U, that are associated with the lowland and upland ecotypes, respectively. The L cytotypes are tetraploids while the U cytotypes can be either tetraploids or octaploids. The objective of this research was to characterize meiotic stability of reciprocal crosses of U and L plants as indicated by chromosome pairing at meiosis and to determine the mode of inheritance of chloroplast DNA (cpDNA) in the hybrids of these cytotypes. Morphological markers that characterize the parents and hybrids also were investigated to confirm that progeny were true hybrids. Reciprocal crosses were made between Kanlow (L tetraploid) and Summer (U tetraploid) plants. Pubescence on the upper surface of the leaf blade, foliage color, and seed size were evaluated as markers to verify hybridization. Meiotic pairing of some of the hybrids was analyzed at the diakinesis stage of meiosis by means of immature anthers. The clone pRR12 from a spinach (Spinacia oleracea L.) cpDNA library was used as a chloroplast hybridization probe to determine chloroplast inheritance. For all the morphological traits evaluated, the hybrids were intermediate in comparison to the parents except for seed width. Chromosome pairing was primarily bivalent in all hybrids. The viability of the hybrid seed and the normal meiotic chromosome pairing of the hybrids indicate a high degree of similarity between upland and lowland genomes. In the cpDNA analysis, all verified hybrids examined carried a fragment identical in size to the fragment of the female parent, indicating predominance of maternal inheritance of the cpDNA in switchgrass

Resposta à flexão e análise de tenacidade de argamassas reforçadas com fibra de Curauá

O desenvolvimento e comercialização de materiais compósitos produzidos a partir de fibras naturais são considerados extremamente importante, uma vez que essas fibras reduzirão a dependência dos materiais produzidos com recursos não renováveis. Dentre essas fibras naturais destaca-se a fibra do curauá, sua utilização na produção de compósitos melhora de forma notável as propriedades do conjunto fibra matriz, logo o presente artigo objetiva estudar as propriedades mecânicas de compósitos reforçados com fibra de curauá, em especial sua resistência à flexão e tenacidade. Para isso foram confeccionadas cinco famílias de argamassas, uma de referência sem utilização da fibra e as outras quatro reforçada com fibra variando o comprimento da fibra e sua fração volumétrica. Verificou-se que a fibra do curauá ao ser adicionada em matriz cimentícia melhora suas propriedades mecânicas comparada a um compósito não reforçado com fibra, sua deformação, resistência à flexão e tenacidade são melhoradas