No description available.

A survey of dipterocarp forest in four sites revealed that the incidence of stem canker was relatively low but high localized incidences were recorded. No consistent association was obtained between the presence of mechanical damage and cankers. Cankers occurred more frequently on dipterocarps and less frequently on euphorbs. Field studies and experimental manipulations were used to compare sapling resistance and responsiveness to wounding and stem breakage in relatively nutrient-rich, alluvial forest and relatively nutrient-poor, sandstone ridge forest. Species found on sandstone ridges showed greater resistance to damage (e.g., greater stem flexibility, narrower crowns) than those on alluvial soils. Species common on alluvial soils tended to be more responsive to damage (e.g., faster wound closure rates, more likely to re-sprout). Results from manipulation experiments conducted on pot-grown seedlings were consistent with results from the field studies, where conditions of greater nutrient availability, saplings closed wounds at faster rates, had less flexible stems, more narrow crowns, and lower levels of foliar total phenolics. Species showed differential rezones to resource availability which, in part, may relate to contrasting strategies for investment in passive defence (i.e., resins and phenolics) over investment in growth. Through their narrower crowns, greater whole stem flexibility, and lesser stem taper, tree species characteristic of sandstone ridges had greater resistance to mechanical damage from debris falling from above than congeneric species characteristic of alluvial soils. Tree species characteristic of alluvial soils were more responsive to damage than congeners on sandstone ridges, by producing earlier and longer sprouts following stem snapping and more rapid rates of wound closure following wounding.

A partir de meados da década de 80, com a expansão da cultura do milho para além das épocas tradicionais de cultivo, quer pela prática da safrinha ou por plantios irrigados, vem ocorrendo um aumento na incidência de doenças a secundária. Dentro deste contexto, o enfezamento vermelho do milho, relatado no país primeiramente em 1970, vem ocorrendo de forma freqüente, apresentando altos índices de ocorrência, muitas vezes com comprometimento total da produção. As plantas infectadas apresentam uma sintomatologia complexa facilmente confundida com viroses. O sintoma mais característico é o avermelhamento foliar. Além do avermelhamento as plantas apresentam redução na altura, perfilhamento basal e axilar, espigas extranumerárias e colmos afinados. Essa doença é causada por um procarioto não cultivável em meio de cultura, habitante exclusivo do floema, denominado fitoplasma, veiculado de forma persistente e propagativa pela cigarrinha Dalbulus maidis. Devido às características do patógeno, a única forma de controle promissora é a utilização de variedades tolerantes/resistentes. Para eficiência na obtenção destas variedades é necessário um diagnóstico correto e conhecimento sobre a variabilidade metodologia mais eficiente tanto para diagnose correta como para investigar essa variabilidade tem sido o PCR. O PCR, utilizando oligonucleotídeos baseados no gene 16SrDNA seguido da análise de RFLP, proporciona uma identificação mente a classificação de fitoplasmas é fundamentada no perfil molecular obtido por análise de RFLP de fragmentos do gene 16SrDNA amplificados. Com base nestas considerações, o trabalho teve como objetivo caracterizar molecularmente isolados do fitoplasma associado ao enfezamento vermelho do milho, coletados em quatro regiões produtoras de milho do estado de São Paulo. A sintomatologia para cada amostra de milho foi anotada. Foram usados dois pares de oligonucleotídeos universais para fitoplasmas em duplo PCR, um par de oligonucleotídeo especificamente desenvolvido para detecção do fitoplasma do enfezamento vermelho do milho, além de oligonucleotídeos para detecção de fitoplasmas pertencentes a grupos específicos. Após amplificação e eletroforese, 29 isolados foram selecionados para a identificação através de RFLP. Fragmentos de DNA foram submetidos à digestão com diferentes enzimas de restrição com o objetivo de identificar/classificar o fitoplasma. Os padrões de bandas obtidos após a eletroforese em gel de poliacrilamida foram comparados com os padrões atuais para classificação dos fitoplasmas. Todos os isolados analisados apresentaram idênticos padrões de bandas, para cada enzima de restrição, considerada individualmente. Não houve diferenciação de acordo com a região geográfica de coleta ou de acordo com intensidade de sintomas apresentados. Todos os isolados foram identificados como pertencentes ao grupo I e subgrupo B da classificação molecular atualmente adotada para estes microorganismos. / Since the middle 80s, an increase in year round cropping of maize resulted in a spread of secondary diseases in the crop’s major production areas. In this context, maize busy stunt, firstly appointed in Brazil in 1970, is occurring more frequently, often with total damage of production. Infected plants show a complex symptomatology, easily confounded with virus-caused diseases. The most characteristic symptom is leaf reddening. Besides the reddening diseased plants show stunting, often developing tillering. This disease is caused by a phytoplasma, a wall- less prokaryote, uncultivable, phloem inhabitant. This pathogen is transmitted by the leafhopper Dalbulus maidis, a in persistent and propagative manner. Due to the pathogen’s characteristics, the best control measure is the use of tolerant/resistant plants. For efficiency in breeding, accurate procedures of detection and an investigation of the pathogen’s genetic variability are necessary. The more accurate manner is using PCR. PCR, using 16SrDNA based primers pairs and followed by RFLP analysis, offers a safe identification of the pathogen. Today the phytoplasma classification is based in molecular patterns obtained by RFLP analysis of amplified 16SrDNA gene fragments. This work’s objective was the molecular characterization of maize bushy stunt phytoplasma strains collected in four corn production areas in São Paulo state, Brazil. The simptomatology to every maize sample was saved. Two primer pairs in nested PCR and a specific primer pair developed to MBS detection were used, besides group specific phytoplasma primers pairs. After amplification and electrophoresis, 29 samples were selected. These selected samples were digested with different restriction enzymes to identify/classify the phytoplasma. The fragment’s sizes obtained by electrophoresis through 4,5% polyacrilamide gel were compared with the reference’s classification patterns. All analyzed samples showed identical fragment-size patterns, for each restriction enzyme considered individually. There was no difference between these samples according to geographic collect region or according to symptoms. All strains were identified as belonging to group I and subgroup B of molecular classification.

No description available.

Thesis (Ph. D.)--University of Adelaide, Department of Plant Pathology, 1985. / Includes bibliographical references (leaves 62-64).

Thesis--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references (p.24-30)

Thesis (Ph.D.)(Microbiology))--University of Pretoria, 2004. / Summary in English. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1958. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 121-126).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1959. / Typescript. Abstracted in Dissertation abstracts, v. 19 (1959) no. 11, p. 2711-2712. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 108-115).