Um novo m?todo para aloca??o de unidade em subamostras representativas baseado em covari?veis discretas.

Em estudos experimentais nos quais se deseja verificar a efic?cia de alguma interven??o, ? usual a presen?a de grupos que sofrer?o ou n?o estas interven??es para que compara??es a respeito de fatores relacionados a estas interven??es possam ser medidos. Para garantir que tais compara??es sejam v?lidas, ? necess?rias que os grupos apresentem caracter?sticas o mais semelhantes poss?vel entre si, definidas no in?cio do estudo. Este trabalho apresenta uma nova metodologia de divis?o, dado um conjunto de dados inicial, em k subamostras representativas em rela??o aos dados iniciais, com base em covari?veis que definem as caracter?sticas desta. Os resultados obtidos constatam que a metodologia de aleatoriza??o proposta apresenta resultados satisfat?rios, principalmente se comparados com a t?cnica tradicional de amostragem aleat?ria simples. As subamostras delineadas pelo m?todo apresentam um alto grau de similaridade com a amostra original, o que possibilitar? aos estudos experimentais deste trabalho uma redu??o no vi?s de sele??o, proporcionando resultados mais satisfat?rios.In experimental studies, like clinic trials, where one wants to verify the eficacy of some intervention, the presence of different groups that will suffer the or not the interventions, so one can make future comparisons. To waranty that the comparisons will be valid, it?s necessary that the groups shows the most similar characteristics among them and the original sample. This study brings a new methodology of division of an original sample in k representative sub-samples about the original sample, based in the covariates that defines the original sample characteristics. The results demonstrate that the proposed methodology shows very satisfatory results, mainly if compared to the traditional method, the random sampling. The sub-samples defined by the new method shows a high similarity with the original sample, which will made possible experimental studies with low selection bias and reliable results

New broad-spectrum resistance to septoria tritici blotch derived from synthetic hexaploid wheat

Septoria tritici blotch (STB), caused by the ascomycete Mycosphaerella graminicola, is one of the most devastating foliar diseases of wheat. We screened five synthetic hexaploid wheats (SHs), 13 wheat varieties that represent the differential set of cultivars and two susceptible checks with a global set of 20 isolates and discovered exceptionally broad STB resistance in SHs. Subsequent development and analyses of recombinant inbred lines (RILs) from a cross between the SH M3 and the highly susceptible bread wheat cv. Kulm revealed two novel resistance loci on chromosomes 3D and 5A. The 3D resistance was expressed in the seedling and adult plant stages, and it controlled necrosis (N) and pycnidia (P) development as well as the latency periods of these parameters. This locus, which is closely linked to the microsatellite marker Xgwm494, was tentatively designated Stb16q and explained from 41 to 71% of the phenotypic variation at seedling stage and 28–31% in mature plants. The resistance locus on chromosome 5A was specifically expressed in the adult plant stage, associated with SSR marker Xhbg247, explained 12–32% of the variation in disease, was designated Stb17, and is the first unambiguously identified and named QTL for adult plant resistance to M. graminicola. Our results confirm that common wheat progenitors might be a rich source of new Stb resistance genes/QTLs that can be deployed in commercial breeding programs

The Physiology and Proteomics of Drought Tolerance in Maize: Early Stomatal Closure as a Cause of Lower Tolerance to Short-Term Dehydration?

Understanding the response of a crop to drought is the first step in the breeding of tolerant genotypes. In our study, two maize (Zea mays L.) genotypes with contrasting sensitivity to dehydration were subjected to moderate drought conditions. The subsequent analysis of their physiological parameters revealed a decreased stomatal conductance accompanied by a slighter decrease in the relative water content in the sensitive genotype. In contrast, the tolerant genotype maintained open stomata and active photosynthesis, even under dehydration conditions. Drought-induced changes in the leaf proteome were analyzed by two independent approaches, 2D gel electrophoresis and iTRAQ analysis, which provided compatible but only partially overlapping results. Drought caused the up-regulation of protective and stress-related proteins (mainly chaperones and dehydrins) in both genotypes. The differences in the levels of various detoxification proteins corresponded well with the observed changes in the activities of antioxidant enzymes. The number and levels of up-regulated protective proteins were generally lower in the sensitive genotype, implying a reduced level of proteosynthesis, which was also indicated by specific changes in the components of the translation machinery. Based on these results, we propose that the hypersensitive early stomatal closure in the sensitive genotype leads to the inhibition of photosynthesis and, subsequently, to a less efficient synthesis of the protective/detoxification proteins that are associated with drought tolerance