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Pseudoperonospora cubensis (Bert. et Curt) Rost. is the causal agent of cucurbit downy mildew (CDM). It is the most damaging cucumber pathogen on the Eastern Shore of Virginia and eastern parts of the United States. Pseudoperonospora cubensis is an obligate oomycete pathogen, infecting crops within the Cucurbitaceae family. The disease is characterized by angular chlorotic lesions and a downy or felt-like appearance on the abaxial side of the leaf. Control of this pathogen includes use of resistant cucumber cultivars and costly fungicide programs. Continuous use has led to resistance to commonly used fungicides. This has become a major concern and in response, seed companies have developed cucumber cultivars which claim downy mildew resistance.  This study evaluates different cucumber cultivars and assesses their level of resistance to CDM. The results indicate that an integrated management approach of reduced fungicide application and the use of resistant cultivars can suppress levels of CDM and yield a cucumber crop. Additionally, a molecular study was conducted, comparing the relative expression of genes encoding a basic PR-1 protein, a cytosolic ascorbate peroxidase protein and three resistance (R) gene proteins, in nineteen cultivars. All of the selected genes were analyzed using real-time PCR. The relative expression levels of the R-genes varied between cultivars. The basic PR-1 protein decreased expression in the majority of the cultivars, suggesting no involvement in the first twenty-four hours. Cytosolic ascorbate peroxidase relative expression levels suggest an increase in susceptible cultivars and a decrease in tolerant cultivars. / Master of Science

Made available in DSpace on 2017-07-25T19:29:57Z (GMT). No. of bitstreams: 1 Monica G Harms.pdf: 1165275 bytes, checksum: cc8059801e06e439fa7ed83ee82ad8db (MD5) Previous issue date: 2013-02-01 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The ideal plants density consists in an extremely important condition in the determining of yield and in the commercial production of onion bulbs. The producers have sought new spatial distributions of plants, aiming harvest bulbs in accord with the size required by the consumer. The plants population have also influence on the development of diseases, because it is associated with the infective units spread of the pathogen and microclimate in culture. The experiment was conducted in the Capão da Onça School Farm aiming to evaluate the influence of plants density and the fungicide use in the occurrence of foliar diseases and the productive characteristics of Bola Precoce cultivar and Bella Dura hybrid. The experimental design was complete randomized blocks, with four replications for the Bola Precoce cultivar and three replications for the Bella Dura hybrid. The treatments were arranged in a split plot design, where the plots were either the presence or the absence of fungicide (metiram + piraclostrobina - 2,5 kg p.c. ha-1) and plant densities (12, 14, 16, 18, 20 and 22 plants m-1) were the split plots. Parameters evaluated were: severity of downy mildew (Peronospora destructor) and purple blotch (Alternaria porri), number of harvest bulbs, bulb mass, bulb diameter, bulb classification and yield. With the data of severity, the area under disease progress curve (AUDPC) was calculated. For Bola Precoce cultivar, no differences were observed between the densities for the parameters AUDPC (downy mildew and purple blotch), purple blotch severity, bulb mass, bulb diameter and bulbs class 0, 2, 3 and 3C. There was difference between densities for downy mildew severity in the evaluation made at 111 days after transplantation (DAT), and the maximum value (34,65%) was found in 15,3 plants m-1 density, in presence of fungicide. The fungicide was effective on downy mildew control in the evaluation made at 97 DAT and on the purple blotch control in the evaluation made at 97 and 104 DAT. The maximum yield was obtained in 22 plants m-1 density, reaching 18,21 and 17,70 t ha-1 in presence and absence of fungicide, respectively. For Bella Dura hybrid, no differences were observed between densities for AUDPC (downy mildew and purple blotch), bulbs class 0, downy mildew severity at 90, 97 and 104 DAT, and purple blotch severity at 90, 97 and 111 DAT. The fungicide was effective in controlling downy mildew in the evaluations made at 97 and 104 DAT. In absence of fungicide, the yield increased with the plant density increasing. In presence of fungicide, the maximum yield (22,09 t ha-1) was obtained in 17,45 plants m-1 density. There was a reduction of the mass and diameter of bulb with the plant density increment, when no fungicide was applied. In presence of fungicide, the percentage of bulbs class 3C decreased with the plant density increase. / A densidade ideal de plantas é extremamente importante na determinação da produtividade e da produção comercial de bulbos de cebola. Produtores têm buscado novas distribuições espaciais de plantas, objetivando colheita de bulbos de acordo com o tamanho exigido pelo consumidor. A densidade de plantas também influencia o desenvolvimento de doenças, pois tem relação com a disseminação das unidades infectivas do patógeno e o microclima na cultura. O experimento foi conduzido na Fazenda Escola Capão da Onça com o objetivo de avaliar a influência da densidade de plantas e o uso de fungicida na ocorrência de doenças foliares e nas características produtivas do cultivar Bola Precoce e do híbrido Bella Dura. O delineamento experimental utilizado foi o de blocos ao acaso com quatro repetições para o cultivar Bola Precoce e três repetições para o híbrido Bella Dura. Os tratamentos foram arranjados em parcelas subdivididas, sendo que as parcelas constituíram a presença ou ausência de fungicida (metiram + piraclostrobina - 2,5 kg p.c. ha-1) e as densidades de plantas (12, 14, 16, 18, 20 e 22 plantas m-1) constituíram as subparcelas. As características avaliadas foram: severidade de míldio (Peronospora destructor) e de mancha púrpura (Alternaria porri), número de bulbos, massa média do bulbo, diâmetro médio do bulbo, classificação dos bulbos e produtividade total. Com os dados de severidade calculou-se a área abaixo da curva do progresso das doenças (AACPD). Para o cultivar Bola Precoce, não foram observadas diferenças entre as densidades para os parâmetros AACPD (míldio e mancha púrpura), severidade de mancha púrpura, massa média do bulbo, diâmetro do bulbo e bulbos classe 0, 2, 3 e 3C. Houve diferença entre densidades para a severidade do míldio na avaliação realizada aos 111 dias após o transplante (DAT), sendo o maior valor (34,65%) encontrado na densidade de 15,3 plantas m-1 na presença de fungicida. O fungicida foi eficiente no controle do míldio na avaliação realizada aos 97 DAT e no controle da mancha púrpura nas avaliações realizadas aos 97 e 104 DAT. A produtividade total máxima foi obtida na densidade de 22 plantas m-1, alcançando 18,21 e 17,70 t ha-1 na presença e ausência de fungicida, respectivamente. Para o híbrido Bella Dura, não foram observadas diferenças entre as densidades para os parâmetros AACPD (míldio e mancha púrpura), bulbos classe 0, severidade de míldio aos 90, 97 e 104 DAT e severidade de mancha púrpura aos 90, 97 e 111 DAT. O fungicida foi eficiente no controle do míldio nas avaliações realizadas aos 97 e 104 DAT. Na ausência do fungicida a produtividade total aumentou com o incremento da densidade de plantas. Na presença do fungicida, maior produtividade (22,09 t ha-1) foi obtida na densidade de 17,45 plantas m-1. Houve redução da massa média dos bulbos e do diâmetro do bulbo com o incremento da densidade de plantas quando o fungicida não foi aplicado. Na presença do fungicida, a porcentagem de bulbos pertencentes à classe 3C diminuiu com o aumento da densidade de plantas.

L’objectif de cette thèse est d’étudier les interactions allélopathiques dans la forêt de chêne pubescente en région méditerranéenne et d’envisager comment ces interactions peuvent être affectées par le changement climatique. Nous avons montré que l'arbre dominant Q. pubescens et ses espèces compagnes A. monspessulanum et C. coggygria ont des potentialités allélopathiques différentes en fonction du stade phénologique des feuilles ce qui pourrait affecter la germination et la croissance des plantes herbacées de sous-étage. Ces différences d'effet allélopathique peuvent résulter non seulement de différences dans la quantité des composés allélopathiques produits, mais aussi de différences qualitatives observées en fonction du stade phénologique. Cela suggère que l’effet allélopathique puisse varier dans le temps de manière à correspondre au stade de développement des plantes herbacées cibles. Sur l’une des plantes cibles utilisées dans les bioessais, les effets allélopathiques ont d’autre part été accentués en changeant les conditions environnementales (hydriques et/ou thermiques) ce qui suggère des modifications éventuelles des potentiels allélopathiques des plantes à attendre avec le changement climatique. Nos résultats en pépinière ont montré le potentiel allélopathique de cotinus et pinus sur la croissance des plantules de chêne, quelques soient les conditions d’arrosage (stressé ou non stressé. En affectant notamment la biomasse du système racinaire dont la croissance est un élément clé des espèces méditerranéennes pour résister à la sécheresse estivale prolongée, ces interactions pourraient jouer un rôle important dans les processus de régénération du chêne pubescent. / The aim of this thesis is to study allelopathic interactions in the downy oak forest in the mediterranean region and to consider how these interactions can be affected by climate change. We have shown that the dominant tree Q. pubescens and its companion species A. monspessulanum and C. coggygria have different allelopathic potentialities, evaluated in vitro on herbaceous target plants, depending on the phenological stage of the leaves, which could in natura affect the germination and growth of understory herbaceous plants. These differences in allelopathic effect may result not only from differences in the quantity of allelopathic compounds produced, but also from qualitative differences observed as a function of the phenological stage. This suggests that the allelopathic effect may vary over time to match the stage of development of the target herbaceous plants. On one of the target plants used in the bioassays, the allelopathic effects were further accentuated by changing the water and / or thermal conditions which suggests possible modifications of the allelopathic potential of the plants to be expected with climate change.Our results in the plant nursery showed the allelopathic potential of cotinus and pinus on the growth of oak seedlings, whatever the watering conditions (stressed or unstressed). By affecting in particular the biomass of the root system, the growth of which is a key element of the mediterranean species to resist the prolonged summer drought, these interactions could play an important role in the regeneration processes of downy oak.

A viticultura no Brasil e no Estado de São Paulo encontra-se em expansão nos últimos 10 anos e a cv. Niagara Rosada (Vitis labrusca) se destaca como principal cultivar para produção de uvas para mesa. Essa cultivar é suscetível à várias doenças foliares, como a ferrugem (Phakopsora euvitis) e o míldio (Plasmopara viticola). Não existem estimativas quantitativas dos danos causados por essas doenças na cv. Niagara Rosada. Diante do exposto os objetivos desse trabalho foram quantificar os efeitos da ferrugem e do míldio nas trocas gasosas, nas limitações da fotossíntese, no acúmulo de biomassa, no acúmulo de carboidratos, e na produção da cv. Niagara Rosada e desenvolver um modelo de simulação para V. labrusca acoplado com os mecanismos de danos da ferrugem e míldio. Experimentos foram conduzidos, separadamente para cada doença, em condições controladas, em mudas inoculadas com diferentes concentrações de P. euvitis e P. viticola e em campo experimental. Medidas de trocas gasosas e curvas de resposta da taxa líquida de assimilação de CO2 ao aumento da concentração intercelular de CO2 (Ci) foram realizadas em mudas sadias e infectadas com P. euvitis e P. viticola. Teores de açúcares solúveis totais, sacarose e amido foram determinados em plantas sadias e inoculadas com os patógenos. P. euvitis e P. viticola reduziram a taxa fotossintética em plantas infectadas tanto na área da lesão como no tecido verde adjacente a lesão (lesão virtual). Valores do parâmetro β, indicativo da lesão virtual, foram de 5,7 e 2,9, respectivamente para P. euvitis e P. viticola. P. euvitis reduziu em 48%, 36% e 67% a atividade da Rubisco (Vcmax), a taxa máxima de transporte de elétrons usados para a regeneraração da RuBP (Jmax) e a condutância do mesofilo (gm), respectivamente, em folhas infectadas. A área foliar e biomassa de raízes em mudas inoculadas com P. euvitis foram reduzidas. Através de análises histopatológicas e da quantificação de amido nas folhas sadias e doentes foi possível observar o acúmulo de amido em regiões adjacentes às pústulas de P. euvitis. Mesmo em baixas severidades da ferrugem já se observam reduções no acúmulo de carboidratos em raízes. P. viticola reduziu Vcmax em 23,5 % em folhas infectadas comparadas às folhas sadias. P. viticola reduziu a biomassa de raízes e quantidade de carboidratos nas raízes de mudas doentes e de plantas no campo em ano de alta severidade da doença. Plantas no campo com sintomas míldio produziram em média 0,5 kg a menos do que plantas sadias e a principal causa da redução na produção foi a queda de bagas causada pela infecção de P. viticola nos cachos. Um modelo de simulação para Vitis labrusca foi desenvolvido, utilizando o software Stella®. A produção, partição e dinâmica da biomassa da videira foi simulada ao longo de 20 anos e os efeitos de P. euvitis e P. viticola na redução do tecido verde sadio da planta, na redução da eficiência fotossintética, no desvio de assimilados, na aceleração da senescência foliar e na queda de frutos foram inseridos no modelo. / Viticulture in Brazil and in the state of São Paulo has increased in the last 10 years and cv. Niagara Rosada (Vitis labrusca) is the main cultivar for the production of table grapes. This cultivar is susceptible to several foliar diseases, such as rust (Phakopsora euvitis) and downy mildew (Plasmopara viticola). There are no quantitative estimates of the damage caused by these pathogens in cv. Niagara Rosada. The objectives of this work were to quantify the effects of rust and downy mildew on gas exchange, photosynthesis limitations, biomass accumulation, carbohydrate accumulation and production of cv. Niagara Rosada and to develop a simulation model for V. labrusca coupled with damage mechanisms caused by rust and mildew. Experiments were conducted, independently for each disease, under controlled conditions in potted plants inoculated with different concentrations of P. euvitis and P. viticola and in experimental field, with natural occurrence of diseases. Measurements of gas exchange and response curves of photosynthetic rate to the increase of the intercellular CO2 concentration (Ci) were carried out in healthy plants and infected plants with P. euvitis and P. viticola. Total soluble sugars, sucrose and starch contents were determined in healthy plants and inoculated plants with the pathogens and kept under controlled conditions. P. euvitis and P. viticola reduced the photosynthetic rate in infected plants both in the area of the lesion and in the green tissue adjacent to the lesion (virtual lesion). Values of parameter β, indicative of the virtual lesion, were 5.8 and 2.9, respectively for P. euvitis and P. viticola. P. euvitis reduced the activity of Rubisco (Vcmax), rate of electrons transport contributing for the RuBP-regeneration (Jmax) and the conductance of mesophyll (gm), respectively, on infected leaves by 48%, 36% and 67%. The severity of P. euvitis reduced leaf area and biomass of plant roots. The histopathological analysis and starch quantification in the leaves allowed to observe starch accumulation in regions adjacent to the pustules of P. euvitis. Even in low disease severities, reductions in carbohydrates accumulation of in roots are already observed. P. viticola reduced Vcmax by 23.5% in infected leaves compared to healthy leaves. P. viticola reduced the root biomass and carbohydrate amounts in the roots of potted plants and plants in the field in the year of high disease severity. Field plants with mildew symptoms produced on average 0.5 kg less than healthy plantsand the main cause of reduction in production was the drop of berries caused by infection of P. viticola in the clusters. A simulation model for Vitis labrusca was developed using Stella ® software. The production, partitioning and dynamics of grapevine biomass was simulated over 20 years and the effects of P. euvitis and P. viticola on the reduction of healthy green plant tissue and photosynthetic efficiency, the assimilative sapper, leaf senescence acceleration and fruit drop were coupled in the model.

Bromus tectorum and other annual brome grasses have invaded many ecosystems of the western United States, and because of an annual-grass influenced alteration of the natural fire cycle on arid western range lands near monocultures are created and conditions in which the native vegetation cannot compete are established. Each year thousands of hectares become near monocultures of annual brome grasses. Pyrenophora semeniperda, a generalist seed pathogen of annual grasses, shows major potential as a possible mycoherbicide that could help in reducing the monocultures created by annual grasses. The purpose of this research was to identify the requirements for isolating cultures of P. semeniperda, search for a hypervirulent strain, and evaluate its effect in the field. The techniques for isolating the fungus have evolved and become more efficient. The first two years of working with P. semeniperda resulted in 11 isolates. During the third year of this study, we developed a single spore isolation technique that resulted in 480 additional isolates. Virulence screening resulted in detection of a range of isolate ability to kill non-dormant B. tectorum seeds. Ninety-two isolates represented a range of virulence from 0-44%. The variation in virulence was expressed mostly within populations rather than between populations. Similarly, virulence varied significantly within Internal Transcribed Spacer (ITS) genotypes and habitats but not between them. When conidial inoculum was applied in the field there was no observed difference in disease incidence between different levels of inoculum. This is thought to have been due to applying the inoculum under conditions in which most in situ seeds were infected and killed by already high field inoculum loads. While additional field trials are needed to optimize the inoculum effectiveness, the overall results of this research provide a good foundation for using P. semeniperda as a biological control for seed banks of annual brome grasses.

A number of technical approaches had to be employed within the planner, namely, 1) translating expected reward into a probability of goal satisfaction criterion, 2) monitoring belief states with a Rao-Blackwellized particle, and 3) employing Rao-Blackwellized particles in the McLUG probabilistic conformant planning graph heuristic. POND-Hindsight is an action selection mechanism that evaluates each possible action by generating a number of lookahead samples (up to a xed horizon) that greedily select actions based on their heuristic value and samples the actions' observation; the average goal satisfaction probability of the end horizon belief states is used as the value of each action.

Typescript / Includes bibliographical references / 134 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Pathology, 1966

Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2007. / Submitted to the African Centre for Crop Improvement. Full text also available online. Scroll down for electronic link.

A viticultura no Brasil e no Estado de São Paulo encontra-se em expansão nos últimos 10 anos e a cv. Niagara Rosada (Vitis labrusca) se destaca como principal cultivar para produção de uvas para mesa. Essa cultivar é suscetível à várias doenças foliares, como a ferrugem (Phakopsora euvitis) e o míldio (Plasmopara viticola). Não existem estimativas quantitativas dos danos causados por essas doenças na cv. Niagara Rosada. Diante do exposto os objetivos desse trabalho foram quantificar os efeitos da ferrugem e do míldio nas trocas gasosas, nas limitações da fotossíntese, no acúmulo de biomassa, no acúmulo de carboidratos, e na produção da cv. Niagara Rosada e desenvolver um modelo de simulação para V. labrusca acoplado com os mecanismos de danos da ferrugem e míldio. Experimentos foram conduzidos, separadamente para cada doença, em condições controladas, em mudas inoculadas com diferentes concentrações de P. euvitis e P. viticola e em campo experimental. Medidas de trocas gasosas e curvas de resposta da taxa líquida de assimilação de CO2 ao aumento da concentração intercelular de CO2 (Ci) foram realizadas em mudas sadias e infectadas com P. euvitis e P. viticola. Teores de açúcares solúveis totais, sacarose e amido foram determinados em plantas sadias e inoculadas com os patógenos. P. euvitis e P. viticola reduziram a taxa fotossintética em plantas infectadas tanto na área da lesão como no tecido verde adjacente a lesão (lesão virtual). Valores do parâmetro β, indicativo da lesão virtual, foram de 5,7 e 2,9, respectivamente para P. euvitis e P. viticola. P. euvitis reduziu em 48%, 36% e 67% a atividade da Rubisco (Vcmax), a taxa máxima de transporte de elétrons usados para a regeneraração da RuBP (Jmax) e a condutância do mesofilo (gm), respectivamente, em folhas infectadas. A área foliar e biomassa de raízes em mudas inoculadas com P. euvitis foram reduzidas. Através de análises histopatológicas e da quantificação de amido nas folhas sadias e doentes foi possível observar o acúmulo de amido em regiões adjacentes às pústulas de P. euvitis. Mesmo em baixas severidades da ferrugem já se observam reduções no acúmulo de carboidratos em raízes. P. viticola reduziu Vcmax em 23,5 % em folhas infectadas comparadas às folhas sadias. P. viticola reduziu a biomassa de raízes e quantidade de carboidratos nas raízes de mudas doentes e de plantas no campo em ano de alta severidade da doença. Plantas no campo com sintomas míldio produziram em média 0,5 kg a menos do que plantas sadias e a principal causa da redução na produção foi a queda de bagas causada pela infecção de P. viticola nos cachos. Um modelo de simulação para Vitis labrusca foi desenvolvido, utilizando o software Stella®. A produção, partição e dinâmica da biomassa da videira foi simulada ao longo de 20 anos e os efeitos de P. euvitis e P. viticola na redução do tecido verde sadio da planta, na redução da eficiência fotossintética, no desvio de assimilados, na aceleração da senescência foliar e na queda de frutos foram inseridos no modelo. / Viticulture in Brazil and in the state of São Paulo has increased in the last 10 years and cv. Niagara Rosada (Vitis labrusca) is the main cultivar for the production of table grapes. This cultivar is susceptible to several foliar diseases, such as rust (Phakopsora euvitis) and downy mildew (Plasmopara viticola). There are no quantitative estimates of the damage caused by these pathogens in cv. Niagara Rosada. The objectives of this work were to quantify the effects of rust and downy mildew on gas exchange, photosynthesis limitations, biomass accumulation, carbohydrate accumulation and production of cv. Niagara Rosada and to develop a simulation model for V. labrusca coupled with damage mechanisms caused by rust and mildew. Experiments were conducted, independently for each disease, under controlled conditions in potted plants inoculated with different concentrations of P. euvitis and P. viticola and in experimental field, with natural occurrence of diseases. Measurements of gas exchange and response curves of photosynthetic rate to the increase of the intercellular CO2 concentration (Ci) were carried out in healthy plants and infected plants with P. euvitis and P. viticola. Total soluble sugars, sucrose and starch contents were determined in healthy plants and inoculated plants with the pathogens and kept under controlled conditions. P. euvitis and P. viticola reduced the photosynthetic rate in infected plants both in the area of the lesion and in the green tissue adjacent to the lesion (virtual lesion). Values of parameter β, indicative of the virtual lesion, were 5.8 and 2.9, respectively for P. euvitis and P. viticola. P. euvitis reduced the activity of Rubisco (Vcmax), rate of electrons transport contributing for the RuBP-regeneration (Jmax) and the conductance of mesophyll (gm), respectively, on infected leaves by 48%, 36% and 67%. The severity of P. euvitis reduced leaf area and biomass of plant roots. The histopathological analysis and starch quantification in the leaves allowed to observe starch accumulation in regions adjacent to the pustules of P. euvitis. Even in low disease severities, reductions in carbohydrates accumulation of in roots are already observed. P. viticola reduced Vcmax by 23.5% in infected leaves compared to healthy leaves. P. viticola reduced the root biomass and carbohydrate amounts in the roots of potted plants and plants in the field in the year of high disease severity. Field plants with mildew symptoms produced on average 0.5 kg less than healthy plantsand the main cause of reduction in production was the drop of berries caused by infection of P. viticola in the clusters. A simulation model for Vitis labrusca was developed using Stella ® software. The production, partitioning and dynamics of grapevine biomass was simulated over 20 years and the effects of P. euvitis and P. viticola on the reduction of healthy green plant tissue and photosynthetic efficiency, the assimilative sapper, leaf senescence acceleration and fruit drop were coupled in the model.