Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, CAPES.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, CAPES.

As algas produzem uma grande diversidade de compostos com atividade biológica, inclusive que agem diretamente sobre vírus ou como indutores de fitoalexinas. Em vista disso, foi investigada a redução de sintomas causados por Tobacco mosaic vírus (TMV) em plantas de fumo tratadas com cianobactérias ou algas eucarióticas, além de se tentar elucidar o modo de ação das algas no patossistema estudado. Quando as plantas de fumo foram tratadas dois dias antes da inoculação, foi verificado que suspensões dos isolados 004/02, 008/02, 061/02, Anabaena sp. e Nostoc sp. 61, bem como as preparações do conteúdo intracelular do isolado 004/02 (4 C) e do filtrado do meio de cultivo do isolado 061/02 (61 M) apresentaram efeito na redução dos sintomas de TMV em plantas de fumo, cultivar TNN. Além disso, foi estudado o efeito direto das algas sobre as partículas de vírus. Os resultados mostraram que os isolados Anabaena sp., Nostoc sp. 21, Nostoc sp. 61 e 090/02 apresentam compostos que agem diretamente sobre o TMV. Para tentar elucidar o mecanismo de ação das algas no patossistema estudado, diversos parâmetros bioquímicos foram investigados. Foi detectado que a preparação 4 C aumentou a atividade de peroxidases e que todos os tratamentos analizados reduziram a atividade de β-1,3-glucanase em folhas de fumo a partir do quarto dia após o tratamento das plantas. Por sua vez, as suspensões dos isolados 008/02 e 061/02 e a preparação 61 M proporcionaram maior acúmulo de superóxido, enquanto que a preparação 4 C reduziu o acúmulo de peróxido de hidrogênio, em relação aos controles água destilada e meio de cultura BG 11, 37 horas após a inoculação do vírus. Em vista disso, as algas podem ser utilizadas como agentes de controle biológico, por apresentar ação direta sobre fitopatógenos ou alterarem o metabolismo de plantas, o que pode estar associado com a sintese de compostos de defesa. / Algae produce several different compounds that show biological activity, including ones with antiviral activity or that act as phytoalexin inducers. Thus, it was investigated the reduction of Tobacco mosaic virus (TMV) symptoms on tobacco plants treated with cyanobacteria or eukaryotic algae, and it was studied the way of action of algae on the studied pathosystem. When the tobacco plants were treated two days before the inoculation, it was verified that the suspension of 004/02, 008/02, 061/02 Anabaena sp., and Nostoc sp. 61 strains as well as the intracellular preparation of 004/02 strain (4 C) and the medium filtrated from 061/02 strain (61 M) reduced TMV symptoms on tobacco plants, cultivar TNN. Furthermore, it was studied the direct effect of the algae suspensions on virus particles. The results showed that Anabaena sp., Nostoc sp. 21, Nostoc sp. 61 and 090/02 strains have compounds with direct activity on TMV. To try to elucidate the way of the action of algae, on the studied pathosystem, several biochemical parameters were investigated. It was seen that the preparation 4 C increase peroxidase activity and all treatments decrease β-1,3-glucanase activity on tobacco leaves from the forth day on after the treatment. Moreover, 008/02 and 061/02 strains and the 61 M preparation caused higher superoxide accumulation, and the preparation 4 C decreased hydrogen peroxide accumulation when compared to the controls distilled water and BG 11 medium 37 hour after virus inoculation. In this way, the algae could be a biocontrol agents, because it shows direct action on phytopathogens and/or change the metabolism of the plants, that could be associated with the synthesis of deffence compounds.

A soja é a cultura de grãos mais importante no Brasil. Na safra de 2010/11 ocupou uma área de 24 milhões de hectares, se destacando como principal oleaginosa produzida e consumida no mundo. Alguns fatores podem limitar a produção da soja, entre eles as doenças. A mancha- alvo (Corynespora cassiicola) é frequente nas em todas as regiões produtoras de soja no Brasil e nos últimos anos tem se atribuído prejuízos crescentes à doença. Os objetivos deste trabalho foram: determinar a faixa ideal de temperatura para o crescimento micelial de diferentes isolados de C. cassiicola; verificar a esporulação em função do meio de cultura; avaliar a germinação de conídios sob diferentes períodos de molhamento foliar; estudar o efeito da temperatura e molhamento foliar nos componentes monocíclicos e realizar estudos de quantificação de danos. Para avaliar o efeito da temperatura no crescimento micelial, diferentes isolados foram mantidos nas temperaturas de 5°C, 10°C, 15°C, 20°C, 25°C, 30°C e 35°C. A temperatura mínima e máxima estimada pela função beta generalizada para o crescimento micelial foi de 6,9°C e 33°C, respectivamente. A esporulação foi estudada nos meios de cultura BDA e Czapek. Os dados obtidos foram comparados por meio do teste Scott-Knott (P<0,05). A produção de conídios foi variável em função do isolado, tanto em meio BDA como Czapek. O ensaio de germinação foi feito em folhas de soja utilizando-se diferentes períodos de molhamento foliar (2, 6, 12, 24, 48 e 72 horas). A contagem de conídios germinados foi feita em microscópio eletrônico de varredura. A germinação de conídios na superfície das folhas foi verificada a partir do período de 6 horas. Para o estudo dos componentes monocíclicos as temperaturas testadas foram 10ºC, 15ºC, 20ºC, 25 ºC e 30ºC e os períodos de molhamento foliar foram 12, 24, 48 e 72 horas. As variáveis quantificadas foram a severidade, o número e o diâmetro das lesões. Os dados foram ajustados às funções beta generalizada e monomolecular. A temperatura mínima, máxima e ótima capazes de promover o desenvolvimento da mancha-alvo foram de 18°C, 32°C e 27°C, respectivamente. O período de molhamemto foliar de 48 horas resultou em maior desenvolvimento da doença. No ensaio de quantificação de danos, cultivares comerciais foram semeadas em duas épocas. Os componentes avaliados em campo foram: a severidade, a área foliar, o indice vegetativo da diferença normalizada (NDVI) e a produtividade (kg ha-1). Com o uso destes dados foram calculadas a área abaixo da curva de progresso da doença (AACPD), a área abaixo da curva de progresso do índice de área foliar (AULIAPC), o indice de área foliar (LAI), o indice de área foliar sadia (HLAI), a duração da área foliar sadia (HAD) e a absorção da área foliar sadia (HAA). Neste ensaio verificou-se que valores de severidade de até 37% no dossel inferior não causam danos no patossistema C.cassicola - soja. As variáveis HLAI e AULAIPC se correlacionaram com a produtividade e podem ser úteis para estudos futuros de quantificação de danos para este patossistema. / Soybean is the most important grain crop in Brazil. The production of 2010/11 occupied an area of 24 million hectares, becoming the most important oilseed produced and consumed worldwide. Some factors, such as diseases, may limit soybean production. The target spot caused by Corynespora cassiicola is frequent in all soybean producing regions in Brazil and in the past years, an increasing loss has been assigned to it. The aims of the present study were to determine the ideal temperature range for mycelial growth of different isolates of C. cassiicola; verify the sporulation in relation to the culture medium; evaluate the conidia germination under different periods of leaf wetness; study the effect of the temperature and the leaf wetness on the monocyclic components and carry out studies of crop loss in the field. In order to evaluate the effect of the temperature on the mycelial growth, different isolates were cultivated at the temperatures of 5°C, 10°C, 15°C, 20°C, 25°C, 30°C and 35°C. The minimum and maximum estimated temperature by the beta function to provide C.cassiicola mycelial growth was 6.9 °C and 33 °C, respectively. The sporulation was analyzed in PDA and Czapek culture media. The results obtained were compared through the Scott-Knott test (P <0.05). The conidia production varied according to each isolate on both PDA and Czapek medias. The germination test was carried out in soybean leaves using different leaf wetness periods (0, 12, 24, 48 and 72 hours). The germinated conidia measurement was done in a scanning electron microscope. The conidia germination on the leaves surface was observed from 6 hours. The temperatures used to study the monocyclic components were 10 º C, 15 º C, 20 º C, 25 º C and 30 º C and the leaf wetness periods were 12, 24, 48 and 72 hours. The variables quantified were severity, number and diameter of lesions. The data were adjusted to the generalized beta and monomolecular functions. The minimum, maximum and optimum temperature able to promote the development of target spot in soybean leaves were 18 ° C, 32 ° C and 27 ° C, respectively. The 48- hour leaf wetness resulted in greater development of the disease. For damage quantification, commercial cultivars were sown in two sowing times. The components evaluated in the field were: severity, leaf area, normalized difference vegetation index (NDVI) and grain yield (kg ha-1). Using these data, it was calculated the area under disease progress curve (AUDPC), area under the leaf area index progress curve (AULIAPC), leaf area index (LAI), healthy leaf area index (HLAI), healthy area duration (HAD) and healthy area absorption area (HAA). The severity values up to 37% in the lower canopy do not cause crop loss in C.cassicola - soybean pathosystem .The variables HLAI and AULAIPC correlated with grain yield and may be useful for future studies of crop loss for this pathosystem.

A Clorose Variegada dos Citros (CVC), causada pela bactéria Xylella fastidiosa, é atualmente a doença de maior incidência no Estado de São Paulo. A incidência e a severidade da doença são maiores nas regiões Norte e Noroeste do Estado, onde o clima é predominantemente quente e com déficit hídrico, principalmente no inverno. Embora não haja nada comprovado, alguns estudos indicam que o déficit hídrico aumenta a severidade dos sintomas nas plantas afetadas pela CVC. Além disso, até hoje não foi estabelecida uma função que relacione doença e dano. Dessa forma, o estudo presente objetivou avaliar o efeito de diferentes níveis de irrigação no progresso poliético da CVC, avaliar métodos de avaliação da doença e determinar uma função de dano para a CVC. Para isso, um experimento foi instalado no município de Bebedouro, região Norte do Estado de São Paulo sob o delineamento blocos ao acaso no esquema fatorial 3 x 2, com os seguintes tratamentos: sem irrigação, irrigado com 50% e 100% da evapotranspiração da cultura (ETc), combinados com inoculação natural e artificial de X. fastidiosa. Cada parcela foi constituída de 6 plantas úteis, havendo 4 repetições de cada tratamento, totalizando 144 plantas úteis. As variáveis quantificadas em cada árvore do experimento foram: (a) produção, considerando frutos assintomáticos e sintomáticos, no período de 2006 a 2008 e produção total referente às safras 2001 a 2005; (b) intensidade da doença, através da incidência de ramos com sintomas da CVC e utilizando uma escala descritiva; (c) vigor da planta, estimado pela medida da altura da planta, diâmetro da copa, diâmetro do tronco, volume de copa e do índice de área foliar (IAF). O modelo monomolecular foi utilizado para descrever o progresso poliético da incidência da CVC, no período de 2006 a 2008, para todos os tratamentos. A partir desse modelo foi possível observar que plantas sem irrigação apresentam maior incidência de ramos com sintomas que plantas irrigadas a 100% da ETc, principalmente quando inoculadas de forma artificial. Esse resultado ficou ainda mais evidenciado quando se avalia o número de frutos com sintomas (ø < 50mm) da CVC por tratamento. Também foi possível observar que os sintomas nas plantas são distribuídos de forma irregular, apresentando um gradiente decrescente significativo da parte superior para inferior. As variáveis relacionadas ao vigor da planta, na sua maioria, não apresentaram relação alguma com a produção em todos os tratamentos. De modo geral, as plantas do tratamento irrigado a 100% da ETc combinado com inoculação natural apresentaram maior produção total, considerando as safras de 2001 a 2008. A relação entre CVC e dano pode ser descrita pela equação (y=114,067*exp(-0,017555)*x) onde y é a produção da planta em Kg e x a incidência de ramos com CVC em porcentagem. A escala descritiva não permitiu avaliação precisa e apresentou baixa correlação entre os avaliadores, o contrário foi observado realizando a avaliação da CVC através da incidência de ramos com sintomas. / The Citrus Variegated Chlorosis (CVC) caused by the bacteria Xylella fastidiosa is nowadays the disease with the most incidence in the state of São Paulo. The incidence and severity of the disease are greater in the Northern and Northwestern regions of the state where the climate is predominately warm and presents a water deficits especially in the winter. Although there is no definite proof, some studies indicate that the water deficits increases the severity of the symptoms in plants affected by the CVC. Besides, up to the present there has not been a function which relates the damage to an intensity of the disease. In that manner, the present study has been conducted in order to evaluate the effect of different irrigation levels on the polyetic progress of the CVC as well as to study methods of assessment of the disease and determine the relationship between disease intensity and yield. In order to carry out this study, an experiment was conducted in the city of Bebedouro north of São Paulo state. The experimental design was in randomized blocks in a 3 x 2 factorial scheme with the following treatments: no irrigation, irrigated with 50% and 100% of the evapotranspiration of the crop (ETc), combined with natural and artificial inoculation of X. fastidiosa. Each group was made of 6 useful plants, with 4 repetitions for each treatment, totalizing 144 useful plants. The variables quantified in each tree of the experiment were: (a) (a) yield, considering asymptomatic and symptomatic fruit in the period 2006 to 2008 and total yield on the crops from 2001 to 2005; (b) intensity of the disease through incidence of branches with symptoms of CVC and using a descriptive scale; (c) plant vigor, estimated through measure of height, crown diameter, trunk diameter, canopy volume and of the leaf area index (LAI). The monomolecular model was used to describe the polyetic progress of CVC incidence between 2006 and 2008 for all treatments. From this model it was possible to observe that plants without irrigation present greater incidence of branches with symptoms than the ones irrigated at 100% of ETc, especially when inoculated in an artificial manner. This result was even more evident when the number of fruit with symptoms is evaluated (ø < 50mm) of CVC per treatment. It was also possible to observe that the symptoms in the plants are scattered in an irregular way, presenting a significant decreasing rate from the upper to the lower part. Most of the variables related to the plant vigor did not present any relation to the production in all treatments. In general, the plants from the irrigated treatment at 100%of ETc combined with natural inoculation presented more total yield considering the harvests from 2001 to 2008. The relationship between CVC and damage can be described by the equation (y=114,067*exp(-0,017555)*x) where y is the plant yield in Kg and x is the incidence in percentage of branches with CVC. The descriptive scale did not allow accurate assessment and showed a low correlation between the raters, the opposite was observed performing the assessment of CVC through the incidence of branches with symptoms.

O objetivo desse trabalho foi quantificar e caracterizar danos pós-colheita em pêssegos comercializados na Companhia de Entrepostos e Armazéns Gerais de São Paulo - CEAGESP e testar produtos sanificantes no controle de podridão parda (Monilinia fructicola) e podridão mole (Rhizopus spp.). Para tanto, foram realizadas vinte avaliações semanais, entre as safras de 2003 e 2004, amostrando-se 1% do total de caixas de pêssegos em cinco permissionários que comercializam esta fruta. As amostragens foram estratificadas por variedade, calibre e produtor. Em todos os frutos de cada amostra foram quantificados os danos abióticos e as doenças pré e póscolheita. Os patógenos Monilinia fructicola e Rhizopus spp. foram cultivados em meio de cultura para realização dos experimentos de controle in vitro e in vivo utilizando cloreto de benzalcônio, dióxido de cloro, Ecolife40&#174; e hipoclorito de cálcio, realizados de forma curativa e preventiva, além do gás ozônio aplicado somente curativamente. A incidência média de frutos danificados foi de 42% em 2003 e 32% em 2004, sendo subdivididos em injúrias mecânicas pré-colheita 18 e 12% em 2003 e 2004, respectivamente, e pós-colheita 12% em 2003 e 13% em 2004; doenças pré-colheita 3 e 1% em 2003 e 2004, respectivamente, e pós-colheita 4% em 2003 e 2% em 2004. O fungo do gênero Cladosporium sp. foi o patógeno que mais ocorreu nas safras avaliadas com 30% em 2003 e 28% em 2004. Injúria mecânica foi o tipo de dano póscolheita mais freqüente em pêssegos. Pêssegos da variedade Aurora foram os mais sensíveis às doenças pós-colheita. Nos testes in vitro cloreto de benzalcônio e Ecolife40&#174;, ambos na concentração de 1000 ppm, inibiram totalmente o crescimento da M. fructicola. Nenhum dos produtos testados foi eficiente no controle de Rhizopus spp. in vitro. Nos testes in vivo, somente o cloreto de benzalcônio na concentração de 2 mL. L-1 e Ecolife40&#174; a 3 mL. L-1, quando aplicados nos pêssegos de forma preventiva, reduziram significativamente a podridão parda em relação à testemunha, em frutos sem ferimento. O cloreto de benzalcônio inibiu a infecção de Monilinia fructicola em todas as concentrações utilizadas, quando aplicado de forma curativa em pêssegos sem ferimento. Hipoclorito de cálcio a 0,1, 0,2 e 0,3 g. L-1 e dióxido de cloro a 2 e 3 mL. L-1 também apresentaram inibição no crescimento de Monilinia fructicola nos testes curativos e inoculados sem ferimentos. Nenhum produto aplicado de forma curativa foi significativamente eficiente para impedir o desenvolvimento da podridão parda, quando a inoculação do fungo foi realizada sobre ferimentos no fruto. Nos experimentos, in vivo, realizados com Rhizopus spp. nenhum dos produtos e formas de tratamentos testados foram eficientes. O gás ozônio não foi eficiente, na concentração de 0,1 ppm, no controle de podridões parda e mole em pêssegos. / The purposes of this study were to quantify and characterize postharvest damages in peaches commercialized at the Companhia de Entrepostos e Armazéns Gerais de Sao Paulo ? CEAGESP, Brazil, as well as to evaluate the effectiveness of sanitizing products in controlling brown rot (Monilinia fructicola) and soft rot (Rhizopus spp.). Twenty weekly evaluations were carried out in 2003 and 2004 and 1% of all peach boxes from five concessionaires was sampled. Samples were stratified according to cultivar, caliber and grower. Every fruit in each sample was assessed as to abiotic damages and pre and postharvest diseases. The pathogens Monilinia fructicola and Rhizopus spp. were grown in culture medium to enable the conduction of the in vitro and in vivo experiments with benzalkonium chloride, chlorine dioxide, Ecolife40&#174; and calcium hypochlorite used curatively and preventively, and ozone gas used only curatively. Average incidences of damaged fruits were 42% and 32% in 2003 and 2004, respectively, involving 18% and 12% pre harvest mechanical injuries, 12% and 13% postharvest injuries, 3% and 1% pre harvest diseases and 4% and 2% postharvest diseases, in 2003 and 2004, respectively. The fungus Cladosporium sp. was the most prevalent pathogen (30% in 2003 and 28% in 2004) in the periods evaluated. Postharvest mechanical injuries were the most common damages in peaches. Peaches cv. Aurora were the most susceptible to postharvest diseases. Benzalkonium chloride and Ecolife40&#174;, both at 1000 ppm, completely inhibited the growth of M. fructicola in in vitro experiments. None of the products tested in this study was effective in the in vitro control of Rhizopus spp. Only the in vivo preventive treatment with benzalkonium chloride at 2 mL. L-1 and Ecolife40&#174; at 3 mL. L-1 promoted significant reduction in brown rot in non-injured peaches when compared to control fruits. The curative use of benzalkonium chloride at all concentrations tested inhibited the infection by Monilinia fructicola in non-injured peaches. The curative application of calcium hypochlorite at 0,1; 0,2 and 0,3 g. L-1 and chlorine dioxide at 2,0 and 3,0 mL. L-1 also inhibited the growth of Monilinia fructicola in non-injured peaches. None of the products tested in curative treatments was significantly effective in preventing the development of brown rot when the fungus was inoculated on injured fruits. None of the products tested was effective in the in vivo control of Rhizopus spp. Ozone gas at 0,1 ppm was not effective in controlling brown rot and soft rot in peaches.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

L’utilisation de pesticides permet de réduire les pertes de récolte mais génère des impacts environnementaux négatifs. Il est important de fournir des informations précises sur les risques épidémiques concernant les bioagresseurs afin de raisonner l’utilisation des pesticides, en particulier dans le cas du mildiou de la vigne, responsable en moyenne de 43% des traitements utilisés dans le Bordelais. Cette thèse évalue l’intérêt de la date d’apparition des symptômes de mildiou de la vigne pour raisonner l’usage des fongicides dans la lutte contre cette maladie.En nous basant sur des observations régionales et de l’expertise locale, nous montrons que dans le Bordelais, les premiers traitements sont réalisés en moyenne quatre semaines avant l’apparition des premiers symptômes. Nous montrons que reporter la date du premier traitement anti-mildiou à la date d’apparition de la maladie permet d’économiser en moyenne 56% des traitements, par rapport aux pratiques actuelles de cette région. Nos résultats montrent que combiner cette stratégie avec le port d’équipements de protection réduit l’exposition des opérateurs de plus de 70%.En utilisant des méthodes de machine learning, nous montrons que la précocité et la gravité des épidémies de mildiou sont fortement liées. Les prévisions de nos modèles peuvent être utilisées pour déclencher les traitements contre la maladie dans les cas de risques élevés, entraînant une réduction de plus de 50% des traitements anti-mildiou par rapport aux pratiques actuelles.Nos résultats et les méthodes employées sont discutés et mis en perspective avec d’autres moyens de réduction de l’usage des pesticides en viticulture. / Abstract: Pesticides reduce yield losses but have negative environmental consequences. It is important to provide precise information on the epidemic risks concerning harmful organisms in order to reason the use of pesticides, in particular in the case of grape downy mildew, which is responsible on average for 43% of pesticides used in Bordeaux vineyards.The objective of this work is to estimate the benefits of using downy mildew onset date to avoid unjustified sprays in the control of this disease. Based on regional observations and local expertise, we show that in Bordeaux, the first treatments are applied on average four weeks before the first symptoms appear.We show that postponing the date of the first downy mildew spray to disease onset reduces fungicide use by an average of 56% compared to current practices in this region. For operators, our results show that combining this strategy with the use of personal protective equipment reduces exposure by more than 70%.By using machine learning methods, we also show that the precocity and severity of downy mildew epidemics are strongly linked. Our predictions can be used to trigger disease treatments only in high-risk cases, resulting in a reduction of more than 50% in mildew treatments compared to current practices. Our results and the used methods are discussed and compared with other methods for reducing the use of pesticides in viticulture.

Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Soilborne diseases of grapevines represent a complex problem with limited information available, both locally and internationally. Previous research in South Africa indicated that Phytophthora and Pythium spp. were the most widespread and devastating pathogens in grapevine nurseries and vineyards in the Western Cape province. The local grapevine industry is currently expanding; new cultivars, methods and agricultural chemicals are being used which can affect soilborne pathogens. It has therefore become necessary to reassess the status of soilborne pathogens in nurseries, since information in this regard is crucial for the development of disease management practices for the expanding local grapevine industry. Soilborne fungal genera associated with roots and crowns of declining nursery grapevines were assessed in surveys conducted at three different grapevine nurseries in the Western Cape province. Cylindrocarpon, Fusarium, Pythium, and Rhizoctonia spp. were consistently isolated from roots and crowns of declining nursery grapevines. Cylindrocladiella spp. and Phytophthora cinnamomi were infrequently isolated from diseased roots, crowns and soil whereas Pythium spp. were abundant in most of the soils. Results suggest that the status of soilborne fungal pathogens in grapevine nurseries in the Western Cape province has changed over the last 30 years. The DNA phylogeny and pathogenicity of the isolates of Cylindrocladiella were determined. Four species of Cylindrocladiella occur on grapevines in South Africa, namely C. lageniformis, C. parva, C. peruviana, as well as a new species, described in this study as C. viticola, which forms part of the C. infestans species complex. Pathogenicity trials were inconclusive. Ten Fusarium spp. were isolated from roots and crowns of declining nursery grapevines, namely F. acuminatum, F. anthophilum, F. chlamydosporum, F. equiseti, F. nygamai, F. oxysporum, F. proliferatum, F. scirpi, F. semitectum and F. solani. The dominant species was F. oxysporum, followed by F. proliferatum and F. solani. In pathogenicity trials F. oxysporum and F. solani significantly reduced root volume, root dry mass, length of new shoots, stem diameter and number of leaves, but increased the percentage of chlorotic leaves and root rot severity. Fusarium proliferatum also caused a significant reduction in new shoot growth, number of leaves and increased root rot severity compared to the controls. Fusarium so/ani seems to be more virulent than F. oxysporum, followed by F. pro/iferatum. This is the first report of F. oxysporum, F. pro/iferatum and F. so/ani as pathogens of grapevines in South Africa, and the first report of F. proliferatum as a pathogen of grapevines in the world. Phytophthora cinnamomi was isolated at low frequencies from declined grapevines, although present in the rhizosphere soil. It is possible that the extensive use of downy mildew chemicals in grapevine nurseries may protect grapevines from infection by P. cinnamomi. The effect of chemicals used to combat downy mildew on Phytophthora root rot of nursery grapevines was evaluated in a glasshouse. There was very little discernable effect of the chemicals tested relative to the control plants for the parameters measured and it was concluded that the inoculation technique needed refinement. However, plants treated with phosphorous acid tended to be taller and have more leaves, greater stem diameter and root volume than controls or plants treated with the other chemicals. The data obtained in this study are not conclusive, but indicated certain trends that more glasshouse trials and field trials would resolve. Results presented in this thesis indicate that a major shift has occurred in the status of soilborne fungi associated with roots and crowns of grapevines in nurseries in the Western Cape since the 1970s when Phytophthora and Pythium were predominant. The prevalence and role of soilborne fungi need to be determined so that new appropriate disease management strategies can be developed to limit losses in grapevine nurseries and ensure the sustainable production of healthy plants for the grapevine industry. / AFRIKAANSE OPSOMMING: 'N ONDERSOEK NA GRONDGEDRAAGDE SWAMME GEASSOSIEER MET WORTELS EN KRONE VAN WINGERD IN KWEKERYE Grondgedraagde siektes van wingerd is 'n komplekse probleem waaroor min inligting, beide plaaslik en internasionaal, beskikbaar is. Vorige navorsing in Suid-Afrika het aangedui dat swamme van die genera Phytophthora en Pythium die mees algemene en vernietigende grondgedraagde patogene in kwekerye en wingerde in die Wes-Kaap provinsie is. Die plaaslike wingerdbedryf brei huidiglik uit; nuwe kultivars, metodes en landbouchemikalieë word gebruik wat 'n invloed kan hê op grondgedraagde patogene. Gevolglik het dit noodsaaklik geword om die status van grondgedraagde patogene in wingerdkwekerye weer te bepaal, aangesien inligting in hierdie verband noodsaaklik is vir die ontwikkeling van siekte bestuurspraktyke vir die ontwikkelende plaaslike wingerdbedryf. Grondgedraagde swamgenera geassosieer met wortels en krone van terugsterwende wingerd in kwekerye is bepaal in opnames wat by drie verskillende wingerdkwekerye in die Wes-Kaap provinsie uitgevoer is. Cylindrocarpon, Fusarium, Pythium, en Rhizoctonia spp. is konstant vanuit wortels en krone van terugsterwende wingerdplante in kwekery geïsoleer, Cylindrocladiella spp. en Phytophthora cinnamomi is ongereeld vanuit siek wortels, krone en grond geïsoleer, terwyl Pythium spp. algemeen in meeste gronde voorgekom het. Resultate dui daarop dat die status van grondgedraagde swampatogene in wingerdkwekerye in die Wes- Kaap provinsie oor die laaste 30 jaar verander het. Die DNA filogenie en patogenisiteit van die isolate van Cylindrocladiella is bepaal. Vier spesies van Cylindrocladiella kom voor op wingerd in Suid-Afrika, naamlik C. lageniformis, C. parva, C. peruviana, sowel as 'n nuwe spesie, wat in hierdie studie as C. viticola aangedui is en wat deel is van die C. infestans spesie kompleks. Patogenisiteits proewe was onvoldoende om die patogeniese status van die swam me te bepaal. Tien Fusarium spp. is vanuit wortels en krone van terugsterwende wingerdplante in kwekery geïsoleer, naamlik F. acuminatum, F. anthophilum, F. chlamydosporum, F. equiseti, F. nygamai, F. oxysporum, F. proliferatum, F. scirpi, F. semitectum en F. solani. Die dominante spesies was F. oxysporum, gevolg deur F. proliferatum en F. solani. In pathogenisteitsproewe het F. oxysporum en F. solani gelei tot 'n betekenisvolle laer wortelvolume, droë massa van wortels, lengte en droë massa van nuwe groei en aantal blare, maar het die persentasie chlorotiese blare en graad van wortelvrot verhoog. Fusarium proliferatum het ook gelei tot 'n betekenisvolle afname in lengte en massa van nuwe groei, aantal blare en 'n verhoogde graad van wortelvrot in vergelyking met die kontrole behandelings. Dit wil voorkom asof Fusarium solani meer virulent is as F. oxysporum, gevolg deur F. proliferatum. Hierdie is die eerste aanmelding van F. oxysporum, F. proliferatum en F. solani as patogene van wingerd in Suid-Afrika, en die eerste aanmelding van F. proliferatum as 'n patogeen van wingerd in die wêreld. Phytophthora cinnamomi is konstant teen lae frekwensies vanuit terugsterwende wingerd in kwekerye geïsoleer, alhoewel dit in risosfeer gronde teenwoordig was. Dit is moontlik dat die ekstensiewe gebruik van chemikalieë teen donsskimmel in wingerdkwekerye die wingerdplante kan beskerm teen infeksie deur P. cinnamomi. Die effek van chemikalieë wat gebruik word teen donsskimmel op Phytophthora wortelverrotting van wingerd in kwekerye, is 'n glashuis geëvalueer. Die chemikalieë wat gestoets is, het vir die gemete parameters, tot baie min onderskeibare effek gelei relatief tot die kontrole plante, en daar is afgelei dat die inokulasie tegniek verbetering benodig. Plante wat met fosforiensuur behandel is, het egter geneig om langer te wees met meer blare, 'n groter stamdeursnee en wortelvolume as kontrole plante of plante behandel met ander chemikalieë. Data verkry vanuit die hierdie studie was onvoldoende, maar sekere neigings is aangedui wat deur verdere glashuis- en veldproewe verklaar sal word. Resultate wat in hierdie tesis weergegee is, het aangedui dat 'n algehele verskuiwing in die status van grondgedraagde swamme geassosieer met wortels en krone van wingerd in kwekerye vanaf die 1970s, toe Phytophthora en Pythium die dominante genera was, plaasgevind het. Die voorkoms en rol van grondgedraagde swamme moet bepaal word, sodat nuwe voldoende siektebestuurspraktyke ontwikkel kan word om verliese in wingerdkwekerye te beperk en sodoende die volhoubare produksie van gesonde plante vir die wingerdbedryf te verseker.

In the genus Fusarium are many important plant pathogens. The diversity of hosts the genus attacks, the number of pathogenic taxa and the range of habitats in which they cause disease are the greatest in plant pathology. One important species complex within the genus Fusarium is Fusarium oxysporum Schlecht. This species complex consists more than 80 pathogenic forma specialis and is particularly difficult to control. The fungi can survive in soil for decades as specialized spores, known as chlamydospores. Interestingly, however, this species complex also contains beneficial non-pathogenic forms that can be exploited to manage Fusarium wilt diseases. In this study, the ability of non-pathogenic F. oxysporum strains, Trichoderma harzianum Rifai Eco-T®, soluble silicon, and their combination was evaluated on two important crops, banana (Musa sp. L.) and beans (Phaseolus vulgaris L.), for their potential to suppress pathogenic strains of F. oxysporum. The ability of these crops to take up and accumulate silicon in their organs, and its effect on low temperature stress was also investigated. Several endophytic fungi, mainly Fusarium spp. and bacteria, were isolated from healthy mature banana plants. After preliminary and secondary in vivo screening tests against F. oxysporum f.sp. phaseoli on beans (Phaseolus vulgaris L.) cv. Outeniqua, two non-pathogenic F. oxysporum strains were selected for further testing. These two non-pathogenic F. oxysporum strains were found to colonize banana (Musa sp.) cv. Cavendish Williams and bean plants, and to suppress Fusarium wilt of these crops. In order to improve the efficacy of these biocontrol fungi, soluble silicon was introduced. The relationship between plant mineral nutrition and plant diseases have been reported by several authors. Plants take up silicon equivalent to some macronutrients, although it is not widely recognized as an essential element. In this study, we established that roots, the target plant organ for soilborne plant pathogens, accumulated the greatest quantity of silicon of any plant organs when fertilized with high concentrations of silicon. On the other hand, the corm and stem accumulated the least silicon. Such observations contradict the concept of passive uptake of silicon via the transpiration stream in these plants as the only uptake mechanism. The prophylactic properties of silicon have been documented for many crops against a variety of diseases. In vitro bioassay tests of silicon against these wilt pathogens showed that silicon can be toxic to Fusarium wilt fungi at high concentrations (>7840 mg .-1), resulting in complete inhibition of hyphal growth, spore germination and sporulation. However, low concentrations of silicon (<490 mg .-1) encouraged hyphal growth. Silicon fertilization of banana and beans significantly reduced disease severity of these crops by reducing the impact of the Fusarium wilt pathogens on these crops. However, it could not prevent infection of plants from the wilt pathogens on its own. Synergistic responses were obtained from combined applications of silicon and non-pathogenic F. oxysporum strains against Fusarium wilt of banana. Combinations of silicon with the non-pathogenic F. oxysporum strains significantly suppressed disease severity of Fusarium wilt of banana, caused by F. oxysporum f.sp. cubense (E.F. Smith) Snyder & Hansen, better than applications of either control measure on their own. Banana production in the subtropical regions frequently suffer from chilling injury, and from extreme variations between night and day temperatures. Such stress predisposes banana plants to Fusarium wilt disease. Silicon, on the other hand, is emerging as important mineral in the physiology of many plants, ameliorating a variety of biotic and abiotic stress factors. We established that silicon fertilization of banana plants significantly reduced chilling injury of banana plants. Membrane permeability, lipid peroxidation (MDA level) and proline levels were higher in silicon-untreated plants than the treated ones, all of which demonstrated the stress alleviating effect of silicon. Low temperatures damage the cell membrane of susceptible plants and cause desiccation or dehydration of these cells. Levels of sucrose and raffinose, recognized as cryoprotectants, were significantly higher in silicon-amended banana plants than unamended plants. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.