Yam (Dioscorea spp.) is considered as a valuable socio-economic crop which has fed thousands of human beings around the world for many centuries with its tubers; thusawarding this crop as source for employment and incomes and a high potential for agroindustrialization, especially in the Brazilian Northeastern region. Facing the lack of research aiming the control of the dry rot disease, the objective of the present work was to evaluate the potential of cassava wastewater and a Bacillus subtilis based bio-nematicide to control the infection of yam seed tubers by Scutellonema bradys and Pratylenchus coffeae in greenhouse conditions, as well as to evaluate the nematicidal activity of aqueous extracts from Annona spp. and Croton heliotropiifolius against S. bradys, verifying the classes of secondary compounds present in these extracts. The experiments were performed in the Laboratory of Phytopathology and the Laboratory of Research in Natural Resources, and in greenhouse at Federal University of Alagoas, Brazil. The first experiment was set-up in a completely random factorial design with five replicates and seven treatments: control without immersion and immersion of seed tubers in cassava wastewater at concentration of 25, 50 and 100% for two periods of 9 and 12 hours, before planting in pots containing sterilized soil. The cyanide content in cassava wastewater was of 3 mg L-1, determined by colorimetric method (Quantofix® Cyanid-Macherey-Nagel). After five months the fresh weight of tuber peel and radicular systems were evaluated, as well as the final population of nematodes in the tuber peels, in the soil and in the plant radicular system. All seed tubers germinated independently of the treatment. Cassava wastewater concentrations of 25% and 25 and 50%, for immersion periods of 09 and 12 hours, respectively, showed significant results for final population of nematodes/g of tuber peels when compared to control. The second experiment was set-up in completely random design with five treatments and four replicates. Treatments were constituted by the commercial bio-nematicide Nemathel® (based on B. subtilis) at the dosages of 50, 200 and 250 mL/10L of water, in addition to the chemical nematicide Carbofuran (40 mL of Furadan® 350 SC/10L of water) as a positive control and without immersion as a negative control. Tubers were immersed 30 minutes for each treatment, then planted in pots containing sterilized soil. After three months the germination of seed tubers was evaluated. The fresh weight of tuber peels and the final population of nematodes in the tuber peel were evaluated five months after planting. One-hundred percent of seed tubers germinated. Treatment of seed tubers with bio-nematicide showed no potential for the bio-control of S. bradys and P. coffeae at the concentrations tested. In the third experiment, three assays were performed to test leaf extracts from: Croton heliotropiifolius, soncoya (Annona purpurea), swamp apple (Annona glabra), sugar apple (Annona squamosa) and wild sugar-apple (Annona mucosa); in addition to stem extracts from C. heliotropiifolius; and tree bark extract from soncoya at concentrations of 0, 25, 50, 75 and 100 %. To test the extracts, 200 μL of each extract and 20 nematodes were placed in the cavities of Kline plates. Twenty-four hours later nematode specimens remaining motionless were quantified and transferred to distilled water, those which did not recover motility after 24 hours of incubation were considered as dead. Chemical screening of the extracts was performed by the preliminary prospection method, performing tests to identify metabolites. The extracts from C. heliotropiifolius stem had no nematicidal effect on S. bradys, while all other extracts caused immobility and mortality of nematodes. Chemical screening showed the presence of flobafenic tannins, flavones, flavonoids, xanthones, flavononols, catechins, flavones, triterpenoids and saponins. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A cultura do inhame (Dioscorea spp.) é considerada de importante valor socioeconômico e, que por vários séculos tem seus rizóforos utilizados na alimentação de milhares de pessoas em todo mundo; o que torna a cultura uma atividade geradora de emprego e renda, com grande potencial para agroindustrialização, sobretudo para a Região Nordeste do Brasil. Diante da carência de pesquisas visando o controle da casca-preta-do-inhame, o presente trabalho teve como objetivos avaliar a potencialidade da manipueira e do bionematicida à base de Bacillus subtilis no tratamento de rizóforos-semente de inhame infectados por Scutellonema bradys e Pratylenchus coffeae em casa de vegetação e ainda, avaliar a atividade nematicida de extratos aquosos de Annona spp. e de Croton heliotropiifolius a S. bradys e verificar as classes de compostos secundários presentes nesses extratos. Para tanto, experimentos foram conduzidos no Laboratório de Fitopatologia e no Laboratório de Pesquisa em Recursos Naturais (LPqRN), e em casa de vegetação do CECA/UFAL. O primeiro foi instalado em delineamento inteiramente casualizado em esquema fatorial com cinco repetições e sete tratamentos: testemunha sem imersão e imersão dos rizóforos-semente em manipueira nas concentrações de 25, 50 e 100% por dois períodos de 9 e 12 horas, seguido do plantio em vasos contendo solo esterilizado. O teor de cianeto na manipueira foi de 3 mg L-1, o qual foi estimado por meio do teste colorimétrico (Quantofix® Cyanid-Macherey-Nagel). Aos cinco meses avaliou-se a massa fresca das cascas dos rizóforos e do sistema radicular e a população final de nematoides na casca dos rizóforos, no solo e no sistema radicular das plantas. A brotação dos rizóforos-semente foi de 100% em todos os tratamentos. As concentrações de manipueira nos dois períodos de imersão (25% - 09 horas; 25% e 50% - 12 horas),apresentaram os melhores resultados em relação à testemunha, para as populações finais dos nematoides/g de casca de rizóforos. O segundo experimento foi em delineamento inteiramente casualizado com cinco tratamentos e quatro repetições. Os tratamentos foram constituídos pelo bionematicida comercial Nemathel® (produto à base de B. subtilis) nas dosagens de 50, 200 e 250 mL/10L de água, além do nematicida químico Carbofurano (40 mL de Furadan® 350 SC/10L de água) como testemunha positiva e sem imersão como testemunha negativa. Os rizóforos foram imersos durante 30 minutos em cada tratamento, posteriormente plantados em vasos contendo solo esterilizado. Aos três meses foi avaliado o percentual de brotação dos rizóforos-semente, e aos cinco meses foi avaliada a massa fresca das cascas de rizóforos e a população final de nematoides nesse material vegetal. Observou-se um percentual de 100% de brotação dos rizóforos-semente. O tratamento dos rizóforos-semente com o bionematicida não apresentou potencial como agente de biocontrole de S. bradys e P. coffeae nas concentrações testadas. Na terceira etapa, foram testados em três ensaios, extratos de folhas de velame (C. heliotropiifolius), soncoya (A. purpurea), araticum-do-brejo (A. glabra), pinha (A. squamosa) e biribá (A. mucosa); extrato de caule de velame; extrato de casca do caule de soncoya, nas concentrações de 0, 25, 50, 75 e 100 %. Em cavidades de placas de Kline foram colocados 200 μL de extrato e 20 nematoides e após 24 horas os espécimes que permaneceram imóveis foram quantificados e transferidos para água destilada, sendo considerados mortos aqueles que não recuperaram o movimento após 24 horas de incubação. A triagem fitoquímica dos extratos foi realizada pela metodologia da prospecção preliminar, realizando testes para identificação de metabólitos. O extrato de caule de velame não apresentou efeito nematicida sobre S. bradys, enquanto os demais causaram imobilidade e mortalidade. A prospecção química demonstrou a presença de taninos flobafênicos, flavonas, flavonois, xantonas, flavononois, catequinas, flavononas, triterpenoides e saponinas.

The degradation of high voltage electrical insulation is a prime factor that can significantly influence the reliability performance and the costs of maintaining high voltage electricity networks. Little information is known about the system of localized degradation from corona discharges on the relatively new silicone rubber sheathed composite insulators that are now being widely used in high voltage applications. This current work focuses on the fundamental principles of electrical corona discharge phenomena to provide further insights to where damaging surface discharges may localize and examines how these discharges may degrade the silicone rubber material. Although water drop corona has been identified by many authors as a major cause of deterioration of silicone rubber high voltage insulation until now no thorough studies have been made of this phenomenon. Results from systematic measurements taken using modern digital instrumentation to simultaneously record the discharge current pulses and visible images associated with corona discharges from between metal electrodes, metal electrodes and water drops, and between waters drops on the surface of silicone rubber insulation, using a range of 50 Hz voltages are inter compared. Visual images of wet electrodes show how water drops can play a part in encouraging flashover, and the first reproducible visual images of water drop corona at the triple junction of water air and silicone rubber insulation are presented. A study of the atomic emission spectra of the corona produced by the discharge from its onset up to and including spark-over, using a high resolution digital spectrometer with a fiber optic probe, provides further understanding of the roles of the active species of atoms and molecules produced by the discharge that may be responsible for not only for chemical changes of insulator surfaces, but may also contribute to the degradation of the metal fittings that support the high voltage insulators. Examples of real insulators and further work specific to the electrical power industry are discussed. A new design concept to prevent/reduce the damaging effects of water drop corona is also presented.