No abstract

Seeding density adjustments is one of the practices that most influence grain yield, as well as other agronomic traits. Therefore, the objective of this study was to determine the ideal plant stand to achieve the maximum grain yield in genotypes showing differential tillering ability. Also, to establish the associations between the genotypes used with tillering and other agronomically important traits as weight of a thousand grains. Two experiments were conducted in 2005 and 2006 in Capão do Leão, Rio Grande do Sul state, Brazil. Five low (JURITI, BR 18, CEP 29, BR 18 and CD 108) and five high (CD 114, SAFIRA, FIGUEIRA, BRS 177 and UMBU) tillering potential wheat cultivars were tested for two years on a split-plot design. The results indicate the need for recommending cultivars based on more than one year of cultivation, especially when dealing with contrasting genotypes for the trait fertile tillers. Regarding the ideal plant stand, seeding density of low tillering ability genotypes ranges from 417 to 555 seeds m -2 , in order to obtain maximum yield and grain weight. On the other hand, for high tillering ability genotypes, the ideal stand ranges from 221 to 422 seeds m -2. These results were year independent. Furthermore, low tillering ability genotypes showed a closer association of number of fertile tillers with grain yield. However, an inverse association was found between number of fertile tillers and weight of a thousand grains.

ResumoAs plantas de trigo utilizam estratégias diferenciadas para a composição do rendimento de grãos. Entre elas se destacam os mecanismos compensatórios entre os componentes do rendimento de grãos: espigas por unidade de área, grãos por espiga e massa de grãos. A produção de grãos em trigo é representada, em grande parte, pela produção de afilhos, desde que as plantas estejam suficientemente espaçadas entre si e haja condições climáticas e de manejo adequadas para estimular um adequado afilhamento. Portanto, se faz necessário o entendimento dos diferentes fatores relacionados à produção e desenvolvimento de afilhos, desde o conhecimento das rotas sinalizantes até as respostas morfo-fisiológicas dos genótipos aos fatores de ambiente, principalmente da qualidade da luz, da fertilidade do solo e da disponibilidade hídrica. O ajuste correto desses fatores, conforme abordado nesta revisão, é de fundamental importância para a maximização da produtividade de grãos. Além disto, parece evidente a necessidade de esforços no melhor aproveitamento de genótipos com reduzido número de afilhos, mesmo com um maior gasto de sementes por hectare, buscando-se a maximização em rendimento de grãos e uma menor dependência das variáveis de ambiente. Palavras-chave: Triticum aestivum L., afilhamento, densidade de semeadura, fatores de ambiente, controle genético e hormonal AbstractWheat plants use different strategies for achieving grain yield. Among them, one can point out the compensatory mechanisms among the grain yield components: number of ears per unity of area, number of grains per ear and grain weight. Grain yield in wheat is mostly represented by tiller production, providing that plants are adequately spaced from each other and that weather conditions are favorable to stimulate tillering. Thus, it is necessary to understand the different factors that are related to tiller production and development. The signalling pathways and the morphophysiological responses to environmental factors such as light quality, soil fertility and water availability are also important. The correct adjustment of these factors, as presented in this review, is essential for maximizing grain yield. In the breeding programs it is important make efforts to use genotypes with low number of tillers, even with a higher number of seeds per hectare, to maximize grain yield, reducing the dependence on environmental variables.

Os objetivos do trabalho foram determinar a adaptabilidade e estabilidade do rendimento de grãos de dez genótipos de trigo (Triticum aestivum L.), contrastantes para o caráter potencial de afilhamento, implantados em diferentes densidades de semeadura. Os experimentos foram realizados nas safras agrícolas de 2005, 2006 e 2007, no município de Capão do Leão (RS) e na safra de 2007 nos municípios de Pato Branco (PR) e Ijuí (RS) Utilizou-se o delineamento de parcelas divididas, com a parcela composta pelo fator cultivar, e as subparcelas pelas densidades de semeadura, com 50, 200, 350, 500 e 650 sementes aptas por metro quadrado. O estudo da adaptabilidade e estabilidade foi realizado por meio do método de Eberhart e Russell. A modificação da densidade de semeadura e o favorecimento do ambiente de cultivo afetaram intensamente os parâmetros de adaptabilidade e estabilidade do caráter rendimento de grãos. Foram constatados genótipos adaptados a todas as densidades de semeadura (FUNDACEP 29 - exceto para 650 sementes m-2), ou com adaptabilidade especifica e comportamento previsível apenas em ambientes favoráveis (CD 114) e ambientes desfavoráveis (CD 108), indicando a necessidade de um ajuste adequado da densidade de semeadura para a resposta e previsibilidade de comportamento quanto ao rendimento de grãos em trigo.

No abstract

IPhenotypic variability of adaptive traits in white oat (Avena sativa L.) in diallelic crosses

No abstract

Sugarcane (Saccharum spp.) bagasse is recognized as a promising feedstock for cellulosic ethanol production. e development of high-quality crop cultivars through plant breeding is a way to improve feedstock quality. is study aimed to directly and indirectly quantify the e ects of agronomic characteristics on the sacchari cation of sugarcane bagasse samples and to identifying the characteristics that can be used as reliable tools for the selection of genotypes for a better biofuel feedstock. e lignin content was determined in bagasse samples of 286 clones from 13 half-sib families. Twenty clones showing a more contrasting lignin content were analyzed for the cellulose and hemicellulose composition in bagasse. ey di ered statistically for cellulose and hemicellulose contents and also for the e ciency of cellulose to glucose conversion. Clones with the highest dry biomass content also had the highest ber content and were grouped among the clones exhibiting the highest lignin content. Lignin content was statistically signi cant and positively correlated with ber (r = 0.485, p < 0.05) and plant biomass (r = 0.654, p < 0.01), and hemicellulose content was statistically signi cant and positively correlated with number of internodes (r = 0.623, p < 0.01). Lignin content and plant biomass had large negative direct e ects (0.405 and 0.784, respectively) on glucose released by enzymatic hydrolysis. Variation among clones for plant productivity parameters and chemical composition of bagasse could be exploited by breeding to increase the amount of cellulosic ethanol produced. Lignin content and plant biomass were the most important components with direct and negative in uences on the conversion of cellulose to glucose.