Дисертації з теми "Orange Diseases and pests"

Includes bibliographical references (leaves 152-164) Microscopy investigations into the oil glands, localisation of the rind oils and the development of oleocellosis have been carried out in Washington navel orange (Citrus sinensis [L.] Osbeck). Aims to develop an improved understanding of the physiological basis of the rind disorder.

Thesis (MScAgric (Horticulture))--University of Stellenbosch, 2010.
ENGLISH ABSTRACT: Creasing, also known as albedo breakdown, is a preharvest disorder that affects the albedo of citrus fruit causing creases on the surface of the fruit. It is a recurrent problem in Navel and Valencia oranges and can cause individual orchard losses which often exceed 50%. Although the contributing factors are known, the physiological basis of creasing development is unresolved and the current control measures do not prevent creasing satisfactory. Hence, better control measures and further understanding of the physiology of creasing development is required. The objective of this two-year study was to determine if the position of fruit in a tree, light and carbohydrate manipulation techniques, and albedo mineral nutrients influence creasing development. Furthermore, the most effective application timing of gibberellic acid (GA3) with the least negative effect on fruit rind colour development and the effectiveness of cytokinins, other products and different root biostimulants to reduce creasing incidence were evaluated. The position of fruit in the tree and light influenced the development of creasing and the distribution of mineral nutrients in the albedo. Creasing incidence was higher on the south side than on the north side of the tree and fruit from the inside sub-sectors had a greater creasing incidence compared to fruit from the outside sub-sectors. The shady part of outside fruit was more creased compared to the sunny part of the fruit and covering fruit with brown paper bags increased creasing severity. The light manipulation techniques used on the leaves and fruit increased the nitrogen (N), phosphorus (P), potassium (K) and manganese (Mn) concentrations in the albedo and differences in the albedo mineral nutrients amongst the sub-sectors evaluated were observed, but creasing severity or creasing incidence was not significantly correlated with the albedo mineral concentrations at harvest. Albedo mineral concentrations earlier in the season may play a role in creasing development, as creasing severity was significantly correlated with copper (Cu), K, and Mn concentrations in the albedo during stage II of fruit development. Creasing incidence and albedo mineral concentrations were not affected by any of the carbohydrate manipulation techniques used in this study. The incidence and severity of creasing was significantly reduced, with a minor negative effect on fruit rind colour development, by the application of GA3, from mid November to mid January. Localised fruit application of CPPU [N-(2-chloro-4-pyridyl)-N-phenylurea], MaxCel (6- Benzyladenine) and CPPU in combination with calcium after physiological fruit drop reduced the incidence and severity of creasing, although creasing incidence was not significantly different from the control. The application of Messenger®, AVG (aminoethoxyvinylglycine) and different root biostimulants did not reduce creasing incidence. The results showed that cytokinins could reduce creasing incidence and justify further studies on application and uptake efficiency. The use of different root biostimulants are not recommended, but it is suggested that treatment effects may be more pronounced over a longer period.
AFRIKAANSE OPSOMMING: Kraakskil is ‘n vooroes abnormalitiet wat die albedo van sitrusvrugte affekteer, deur krake op die oppervlak van vrugte te veroorsaak. Dit is ‘n algemene probleem in Navel en Valencia lemoene en kan boordverliese van tot 50% of soms hoër veroorsaak. Alhoewel die bydraende faktore bekend is, is die fisiologiese basis van kraakskil ontwikkeling onopgelos en die beskikbare beheermaatreëls is nie bevredigend nie. Dus, beter beheermaatreëls en ‘n beter begrip van die fisiologie van kraakskil ontwikkeling is nodig. Die doel van die twee-jaar studie was om te bepaal of die posisie van vrugte in ‘n boom, lig en koolhidraat manipulasie tegnieke en minerale elemente in die albedo, kraakskil ontwikkeling beïnvloed. Die mees effektiewe toedieningstyd van gibberelliensuur (GA3) sonder ‘n negatiewe effek op vrugkleur is bepaal en die effektiwiteit van sitokiniene, ander produkte en verskillende wortel biostimulante om kraakskil voorkoms te verminder, is geëvalueer. Die posisie van vrugte in ‘n boom en lig het kraakskil ontwikkeling en die verspreiding van minerale element in die albedo beïnvloed. Kraakskil voorkoms was hoër aan die suidekant van die boom as aan die noordekant en vrugte in die binnekant van die boom het ‘n groter kraakskil voorkoms as vrugte in die buitekant van die boom gehad. Die skadukant van buitevrugte het meer kraakskil gehad as die sonkant en die toemaak van vrugte met ‘n bruin papiersak het die graad van kraaksil verhoog. Die lig manipulasie tegnieke wat op die blare en vrugte gebruik is, het die stikstof (N), fosfaat (P), kalium (K) en mangaan (Mn) konsentasies in die albedo verhoog en verskille in die albedo minerale elemente tussen sub-sektore is waargeneem, maar betekenisvolle korrelasies is nie tussen die graad en voorkoms van kraakskil en die albedo minerale element konsentrasies by oestyd waargeneem nie. Albedo minerale element konsentrasies vroeër in die seisoen mag ‘n rol speel by kraakskil ontwikkeling, omdat die graad van kraakskil betekenisvol gekorreleer was met albedo koper (Cu), K, en Mn konsentrasies tydens fase II van vrugontwikkeling. Kraakskil voorkoms en albedo minerale element konsentrasies is nie deur enige van die koolhidraat manipulasie tegnieke geaffekteer nie. Die voorkoms en graad van kraakskil is betekenisvol verlaag, met ‘n geringe negatiewe effek op vrugkleur, deur die toediening van GA3 vanaf mid November tot mid Januarie. Gelokaliseerde vrugtoedienings van CPPU [N-(2-chloro-4-piridiel)-N-phenielureum], MaxCel (6- Bensieladenien) en CPPU saam met kalsium na fisiologiese vrugval het die voorkoms en graad van kraakskil verlaag, alhoewel kraakskil voorkoms nie betekenisvol van die kontrole verskil het nie. Die toediening van Messenger®, AVG (amino etoksievinielglisien) en veskillende wortel biostimulante het nie kraakskil voorkoms verlaag nie. Die resultate het getoon dat sitokiniene kraakskil voorkoms kan verlaag en verdere studies op die toediening en opname effektiwiteit word aanbeveel. Die gebruik van verskillende wortel biostimulante word nie aanbeveel nie, maar die effek behoort meer sigbaar te wees na ‘n langer periode van behandeling.

Orientador: Leda Maria Caira Gitahy
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Geociências
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Resumo: O objetivo desta tese é entender o processo de transformação na cadeia produtiva da laranja no estado de São Paulo a partir da análise das mudanças tecnológicas introduzidas no setor produtor de laranja ao longo dos anos 2000. O estudo foca as mudanças tecnológicas relativas ao combate de doenças na lavoura citrícola, buscando analisar as controvérsias e as relações de poder presentes no processo de apropriação dessas tecnologias. As negociações em torno das formas de combate à doença da laranja conhecida como Huanglongbing (HLB ou greening) constituem o estudo de caso central na tese. O trabalho combinou a utilização de duas abordagens teóricas distintas: a cadeia global de mercadorias (global commodity chains) e a teoria ator-rede (actor network theory). A investigação também compreendeu a análise de dados empíricos a partir da realização de pesquisa de campo com diferentes estratos de produtores rurais de laranja e representantes institucionais da cadeia. Foi possível verificar que as políticas fitossanitárias de combate ao greening divulgadas pelos órgãos públicos e entidades representantes do setor não conseguiram conter o avanço da doença. Estes falharam em traduzir os interesses dos atores envolvidos na produção da laranja ao reduzir o controle a uma questão técnica desconsiderando o quadro de crise e de ampliação de assimetrias de poder na cadeia produtiva. Apesar da base técnica de controle de doenças adotada no setor apresentar sinais de esgotamento, medidas alternativas de controle esbarram nas exigências competitivas ditadas pelo modelo agrícola do setor e pela estrutura de governança da cadeia produtiva de laranja. Com o avanço do greening pelo estado de São Paulo desencadeia-se um processo de transformação sócio-técnica na cadeia produtiva da laranja cujas características principais são a crescente tecnificação do processo de produção e a ampliação das barreiras à permanência de produtores no setor
Abstract: The aim of this thesis is to understand the current transformation process in the orange production chain in Sao Paulo state on the basis of an analysis of technological changes in the sector over the years 2000. The study focuses on the technologies designed to combat diseases in citrus crops, trying to analyze the controversies and power relations present in the process of adoption of these technologies. Negotiations over the ways to combat the citrus disease known as Huanglongbing (HLB or greening) are the central case study in the thesis. The study combined the use of two distinct theoretical approaches: global commodity chains and actor network theory. The investigation also included the analysis of empirical data gathered through field research conducted with different strata of orange producers and institutional representatives of the productive chain. It was verified that the phytosanitary policies conducted by public entities and institutional representatives to combat the greening failed to contain the spread of the disease. These policies failed to translate the interests of the actors involved in orange production because they limited the combat of the disease to a technical issue ignoring the context of the crisis and the expansion of power asymmetries in the orange production chain. Despite the technical basis of disease control have shown signs of exhaustion, the adoption of alternative methods of control were restricted by the competitive requirements dictated by the "modern" agriculture pattern and the governance structure of the productive chain. With the spread of citrus greening disease in São Paulo state, there is the onset of a socio-technical transformation in the orange production chain, which main features are the increasing technification of the orange production process and the growing barriers to the stability of the current producers in the sector
Doutorado
Politica Cientifica e Tecnologica
Doutora em Política Científica e Tecnológica

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Tylenchulus semipenetrans é o principal nematoide em citros, causando perdas que variam de 10 a 30%. Está amplamente disseminado nos pomares citrícolas do Brasil. Para determinar o nível populacional desse nematoide, que varia durante o ano, diferentes variáveis são utilizadas. Sendo assim o objetivo deste trabalho foi avaliar a flutuação populacional do nematoide T. semipenetrans em pomar de laranja ‘Pera Rio’ enxertada em limoeiro ‘Cravo’, correlacionar a população do nematoide no final de cada estação com a produção e correlacionar o número de fêmeas na raiz com o número de juvenis encontrados nas amostras de solo e raiz. As amostragens foram realizadas no final de cada estação climática, durante a safra 2011/2012, numa profundidade de 0-30 cm, na projeção da copa de 10 plantas sem sintomas, 10 com sintomas e as adjacentes das sintomáticas, totalizando 60 plantas. Os nematoides presentes no solo foram extraídos pela metodologia de flutuação em centrifuga e das raízes pela técnica do liquidificador e centrifugação. Os frutos de cada planta foram colhidos separadamente e pesados. Para contagem das fêmeas, 1g de raiz de cada amostra foi submetida à coloração para facilitar a contagem. O número de nematoides no solo e na raiz foram plotados em gráficos e correlacionados com dados de temperatura e precipitação pluviométrica pela análise de Pearson; os dados de peso de fruto por planta e número de nematoides em solo...
Tylenchulus semipenetrans is the main nematodes in citrus trees, causing losses ranging from 10 to 30%. It is widespread in the citrus orchards of Brazil. To determine the level of nematode population which varies over the year, different variable are used. Therefore the objective of this study was to evaluate the fluctuation of nematode T. semipenetrans on acreage with orange ‘Pera Rio’ grafted on ‘Rangpur’, correlate the nematode population at the end of each season with the production and correlate the number of females in the root with the number of juveniles found in soil samples and root . Samples were taken at the end of each season climate, during the 2011/2012 season, at a depth of 0-30 cm, the crown projection of 10 plants without symptoms, 10 with symptoms and symptomatic adjacent plant, totaling 60 plants. The nematodes in the soil were extracted by centrifugal flotation method and the technique of the roots of the blender and centrifugation. The fruits of each plant were harvested and weighed separately. To count the number of females in the roots, 1g of each root sample was colored and subsequently dried. The number of nematodes in soil and roots were plotted on graphs and correlated with data on temperature and rainfall by Pearson analysis, the data for fruit weight per plant and the number of nematodes in soil and roots, on each season, were transformed and analyzed by Spearman correlation, considering both the significance level of 5%. The data on soil nematode, root nematode, sum of soil and root nematode and females per gram of root were analyzed by Pearson correlation analysis and subsequent to the correlation matrix. In the region of Botucatu, central western state of São Paulo, the largest population level of the citrus nematode occurred in late winter and lowest in late spring, and the nematodes... (Complete abstract click electronic access below)

Orientador: Silvia Renata Siciliano Wilcken
Banca: Sarita Leonel
Banca: Claudio Marcelo Gonçalves de Oliveira
Resumo: Tylenchulus semipenetrans é o principal nematoide em citros, causando perdas que variam de 10 a 30%. Está amplamente disseminado nos pomares citrícolas do Brasil. Para determinar o nível populacional desse nematoide, que varia durante o ano, diferentes variáveis são utilizadas. Sendo assim o objetivo deste trabalho foi avaliar a flutuação populacional do nematoide T. semipenetrans em pomar de laranja 'Pera Rio' enxertada em limoeiro 'Cravo', correlacionar a população do nematoide no final de cada estação com a produção e correlacionar o número de fêmeas na raiz com o número de juvenis encontrados nas amostras de solo e raiz. As amostragens foram realizadas no final de cada estação climática, durante a safra 2011/2012, numa profundidade de 0-30 cm, na projeção da copa de 10 plantas sem sintomas, 10 com sintomas e as adjacentes das sintomáticas, totalizando 60 plantas. Os nematoides presentes no solo foram extraídos pela metodologia de flutuação em centrifuga e das raízes pela técnica do liquidificador e centrifugação. Os frutos de cada planta foram colhidos separadamente e pesados. Para contagem das fêmeas, 1g de raiz de cada amostra foi submetida à coloração para facilitar a contagem. O número de nematoides no solo e na raiz foram plotados em gráficos e correlacionados com dados de temperatura e precipitação pluviométrica pela análise de Pearson; os dados de peso de fruto por planta e número de nematoides em solo... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Tylenchulus semipenetrans is the main nematodes in citrus trees, causing losses ranging from 10 to 30%. It is widespread in the citrus orchards of Brazil. To determine the level of nematode population which varies over the year, different variable are used. Therefore the objective of this study was to evaluate the fluctuation of nematode T. semipenetrans on acreage with orange 'Pera Rio' grafted on 'Rangpur', correlate the nematode population at the end of each season with the production and correlate the number of females in the root with the number of juveniles found in soil samples and root . Samples were taken at the end of each season climate, during the 2011/2012 season, at a depth of 0-30 cm, the crown projection of 10 plants without symptoms, 10 with symptoms and symptomatic adjacent plant, totaling 60 plants. The nematodes in the soil were extracted by centrifugal flotation method and the technique of the roots of the blender and centrifugation. The fruits of each plant were harvested and weighed separately. To count the number of females in the roots, 1g of each root sample was colored and subsequently dried. The number of nematodes in soil and roots were plotted on graphs and correlated with data on temperature and rainfall by Pearson analysis, the data for fruit weight per plant and the number of nematodes in soil and roots, on each season, were transformed and analyzed by Spearman correlation, considering both the significance level of 5%. The data on soil nematode, root nematode, sum of soil and root nematode and females per gram of root were analyzed by Pearson correlation analysis and subsequent to the correlation matrix. In the region of Botucatu, central western state of São Paulo, the largest population level of the citrus nematode occurred in late winter and lowest in late spring, and the nematodes... (Complete abstract click electronic access below)
Mestre

Stony corals (Order Scleractinia) are susceptible to a variety of diseases, which can occur from abiotic or biotic factors, or a combination of both. Public aquaria provide opportunities to study coral disease. Because coral mucus is the first line of defense against disease, the Biolog EcoplateTM is a useful tool to detect differences in microbial assemblages in the surface mucopolysaccharide (mucus) layer when comparing healthy and diseased corals. Histological examination is essential to document structural changes in coral tissue in response to diseases. This study identifies and characterizes diseases in captive corals through visual recognition, characterization of carbon utilization by microbial assemblages in coral mucus samples, and histological examination. In March 2010, surveys were sent to public aquaria throughout the United States that house corals. If the survey was returned indicating that the aquarium had diseased coral specimens present, sample kits were sent to the aquarium to acquire photographs, mucus samples for microbial carbon utilization analysis, and tissue samples for histological examination. Eighteen aquaria participated in the survey and 25 sets of samples were provided. The gross lesions from diseased samples fit into six categories: discoloration associated with darkening of the tissue or with color loss (bleaching), growth anomalies, and tissue loss associated with pests, with brown jelly, or with no obvious cause. Seven categories of possible contributing factors were reported: addition of inadequately quarantined corals to the tank, damage during transport, change of location, manual stress, and variations in light, salinity, or temperature. Introduction of inadequately quarantined specimens was the most common possible contributing factor to pest introduction. Significant differences in carbon source utilization were found between tank-water samples and mucus from both healthy and diseased areas of sampled corals. Although mucus samples from healthy and diseased samples did not differ in carbon source utilization overall, D-mannitol was used by 52% of microbial assemblages from mucus from diseased areas compared with only 17% of microbial assemblages from healthy mucus samples. Histologically, the most commonly observed features across all samples were healthy zooxanthellae, endolithic organisms, and nematocysts, all of which are normal features that can be influenced by stress factors. Brown granular material and ciliates were found associated with some anomalies, primarily the three categories of tissue loss. The presence of dense aggregates of zooxanthellate-engorged ciliates in corals afflicted with brown jelly was highly similar to histological observations of brown band syndrome, previously described from natural coral reefs.

Los terpenos constituyen el mayor grupo de metabolitos secundarios, siendo componentes de las glándulas de aceites esenciales, de las flores y de las resinas defensivas de plantas aromáticas, a los que proporcionan sus aromas y sabores característicos. Los terpenos volátiles se asocian a la defensa de muchas especies de plantas, animales y microorganismos contra depredadores, patógenos y competidores. Por otra parte, estos compuestos parecen servir como señales para atraer a los polinizadores y agentes dispersores de semillas, así como a depredadores de plagas. El estudio de compuestos orgánicos volátiles emitidos durante el desarrollo del fruto y después del desafío con diferentes agentes bióticos puede ayudar a conocer las interacciones de los frutos carnosos no sólo con vertebrados dispersores y depredadores, sino también con insectos y microorganismos. Los frutos carnosos son particularmente ricos en volátiles. En los frutos cítricos, los monoterpenos son los principales componentes de las glándulas del aceite esencial de la cáscara (flavedo), siendo el D-limoneno el más abundante (hasta 95% en la naranja). Esta característica hace que los cítricos sean un buen sistema modelo para el estudio de la función de los terpenos en los frutos. La biología molecular moderna permite la realización de experimentos para comprobar la función de terpenos por medio del uso de organismos transformados genéticamente en los que se han manipulado los niveles de acumulación de dichos compuestos. En este trabajo, se ha utilizado un plásmido que alberga el cDNA completo del gen de una limoneno sintasa de cítricos (CiTMTSE1) en orientación antisentido (AS) o sentido (S) para modificar la expresión y la acumulación de D-limoneno en plantas de naranjo dulce (Citrus sinensis L. Osb.). La acumulación de D-limoneno en las frutas AS se redujo drásticamente pero la acumulación de otros terpenos también se modificó, afectando a compuestos tales como alcoholes monoterpenos, cuya concentración se incrementó en la cáscara de las frutas. Las plantas transformadas fueron morfológicamente indistinguibles de las plantas control (WT) y de las plantas transformadas con el vector vacío (EV). Los frutos transgénicos fueron desafiados con un insecto plaga y con diferentes patógenos para probar si la alteración de los niveles de acumulación de estos volátiles daba como resultado una mejora en la respuesta del flavedo frente a plagas y patógenos. Los machos de la mosca mediterránea de la fruta (Ceratitis capitata) expuestos a las frutas AS y EV en ensayos en túnel de viento fueron significativamente más atraídos por el aroma de los frutos control EV. En otros experimentos de desafío con el hongo de la podredumbre verde Penicillium digitatum y la bacteria causante de la cancrosis de los cítricos Xanthomonas axonopodis subsp. citri, las frutas transgénicas con un contenido reducido de D-limoneno mostraron elevada resistencia a estos patógenos. El alto contenido en D-limoneno en la cáscara de naranjas maduras puede ser una señal para la atracción de plagas y microorganismos que podrían estar involucrados en la facilitación del acceso a la pulpa de los frugívoros dispersores de semillas. El análisis de la expresión génica global en el flavedo de las frutas transgénicas vinculó la disminución de D-limoneno y la reducción de la expresión de genes del metabolismo de monoterpenos con la activación de la expresión de genes implicados en inmunidad innata, incluyendo factores de transcripción, genes de quinasas implicadas en la entrada de Ca2+ en la célula y genes implicados en la activación de las cascadas de MAPKs, con la consiguiente activación de la ruta de señalización de ácido jasmónico (JA), lo que provocó la activación del metabolismo de JA y un aumentó drástico de la acumulación de JA en la cáscara de la naranja tras el desafío con P. digitatum, lo que explicaría la resistencia al menos a hongos necrotrofos observada en las frutas. Estos resultados indican que la acumulación de D-limoneno en la cáscara de la naranja estaría implicada en la interacción trófica entre las frutas, insectos y microorganismos, lo cual proporciona una visión mucho más amplia de las funciones de los terpenos en la naturaleza. También representa una alternativa muy prometedora para incrementar la resistencia o tolerancia de las plantas frente a patógenos y plagas.
Terpenes, the largest group of secondary metabolites, are well known as constituents of essential oils, floral scents and defensive resins of aromatic plants, to which they impart their characteristic aromas and flavors. Terpene volatiles defend many species of plants, animals and microorganisms against predators, pathogens and competitors. Moreover, those compounds seem to serve as advertisements to attract pollinators and seed-dispersal agents as well as pest predators. The study of VOCs emitted during fruit development and after challenge with different biotic agents may help to determine the interactions of fleshy fruits not only with legitimate vertebrate dispersers and predators, but also with insects and microorganisms. Fleshy fruits are particularly rich in volatiles. In citrus fruits, monoterpenes are the main components of the essential oil glands of the peel, being D-limonene the most abundant one (up to 95% in orange fruits). This characteristic makes citrus a good model system for studying the function of terpenes in plants. Modern molecular biology now enable experiments to test terpenoid function by the use of genetically transformed organisms in which terpene levels have been manipulated. In this work, a plasmid harboring the complete cDNA of a citrus limonene synthase gene (CiTMTSE1) in antisense (AS) or sense (S) orientation was used to modify the expression and accumulation of D-limonene of sweet orange (Citrus sinensis L. Osb) plants. D-limonene accumulation in AS fruits was dramatically reduced but the accumulation of other terpenoids was also modified, such as monoterpene alcohols, whose concentration increased in the peel of fruits. Genetically transformed plants were morphologically indistinguishable from wild-type (WT) and empty vector (EV) control plants. Transgenic fruits were challenged against a pest and different pathogens to test whether volatile profile alteration results in an improvement in the response of the fruit flavedo against them. Males of the Mediterranean fruit fly (Ceratitis capitata) exposed to AS fruits versus EV in wind tunnel assays were significantly more attracted to the odor of EV control fruits. In separate experiments with the green mould rot of citrus fruits and citrus canker caused by Penicillium digitatum and Xanthomonas axonopodis subsp. citri, respectively, transgenic fruits with a reduced content in D-limonene showed resistance to both pathogens. High D-limonene content in mature orange peels may be a signal for attractiveness of pests and microorganisms which might be likely involved in facilitating the access to the pulp of seed dispersal frugivores. A global gene expression analysis of the flavedo of AS transgenic fruits linked the decrease of D-limonene and monoterpene metabolism to the up-regulation of genes involved in the innate immunity response, including transcription factors together with Ca2+ entry into the cell and activation of MAPK cascades, contributing to activation of jasmonic acid (JA) signaling, which triggered the up-regulation of JA metabolism and drastically increased the accumulation of JA in orange peels upon fungal challenge, explaining the resistance to necrotrophic fungi observed in AS fruits. These results indicate that limonene accumulation in the peel of citrus fruit appears to be involved in the successful trophic interaction between fruits, insects, and microorganisms and provide a much more comprehensive view of roles of terpenes in nature. It also represents a very promising alternative for increasing resistance or tolerance of plants to pathogens.
Rodríguez Baixauli, AM. (2013). Genetic engineering of plant volatiles in fleshy fruits: pest repellency and disease resistance through D-limonene downregulation in transgenic orange plants [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/31655
TESIS

Dissertation (PhD (Agric))--University of Stellenbosch, 2002.
ENGLISH ABSTRACT: Fungi belonging to the genus Botryosphaeria are heterotrophic micromycetes that can be pathogens on woody plants. They cause serious, and in some cases devastating losses to crops through leaf necrosis, stem cankers and plant death. The Proteaceae cut-flower industry in South Africa accounts for 70% of the national cut-flower enterprise. Botryosphaeria diseases are a major impediment to production and trade of Proteaceae and there is an urgent need to investigate the etiology, epidemiology and control of these diseases. Losses of one of the most important proteas, P. magnifica, amount to 50% or more, locally. The main aims of this study were therefore to establish the etiology and aspects of epidemiology of Botryosphaeria stem cankers on P. magnifica and other Proteaceae, and to investigate methods of disease control. Although there is a vast body of information pertaining to this fungus, which was reviewed in Chapter 1, there is relatively little information available on Botryosphaeria on Proteaceae. The taxonomy of Botryosphaeria requires thorough review, and molecular techniques need to be employed to resolve species identities. In Chapter 2, it was found that Phyllachora proteae, a leaf pathogen of proteas, produced a Fusicoccum anamorph, which is described as F. proteae. A sphaeropsis-like synanamorph was associated with F. proteae and a new combination for P. proteae is proposed in Botryosphaeria, as B. proteae. The taxonomy of Botryosphaeria is in disarray at both the generic and the specific level. In Chapter 3 the taxonomic history of Botryosphaeria is reviewed, and the genus circumscribed and distinguished from other morphologically similar genera. Although several anamorph genera have been linked to Botryosphaeria, based on morphological observations and phylogenetic analysis of lTS rDNA sequence data, two anamorph genera are now recognised, those with pigmented conidia (Diplodia), and those with hyaline conidia (Fusicoccum). Botryosphaeria proteae should thus be excluded from Botryosphaeria. Several pathogenic Botryosphaeria spp. have an endophytic phase within their hosts. They are therefore imported unwittingly into other countries where they may pose a risk to agriculture and indigenous vegetation. The current global distribution of Botryosphaeria spp. associated with Proteaceae is clarified and a key to these taxa associated with Proteaceae is provided in Chapter 4. Five Botryosphaeria spp. are associated with cut-flower Proteaceae worldwide viz. B. lute a, B. obtusa, B. protearum, B. proteae and B. rib is. B. protearum is described as a new species. A thorough understanding of disease epidemiology is essential to effect a reduction of losses. In Chapter 5, I show that on P. magnifica, lesions caused by Botryosphaeria protearum, which lead to the formation of stem cankers, are initiated in the mid-rib vein or margin of leaves. Koch's postulates were satisfied and it was found that the number of lesions that developed from artificial inoculations correlated with starch levels present in leaves at the time of inoculation. In Chapter 6 it is shown that B. protearum exists as an endophyte in leaves of P. magnifica in naturally occurring as well as cultivated plants. In natural stands of proteas stem cankers are rare, but in cultivated plantations the incidence is high. Nutritional analyses indicate that higher levels of nitrogen occur in leaves of cultivated plants in spring, which could enhance disease development. High levels of sodium in the leaves of wild plants may restrict disease development. The severe economic losses caused by B. protearum make the search for improved methods of disease control essential. Fungicide applications form an important component of an integrated approach to disease management. In Chapter 7, in vitro tests demonstrate that tebuconazole, benomyl, prochloraz me, iprodione and fenarimol reduce the mycelial growth of B. protearum effectively. In the field there was a 25-85% reduction in the occurrence of stem cankers by applying fungicides or sanitation pruning. The best control was achieved by using benomyl, bitertanol, fenarimol, iprodione, prochloraz manganese chloride alternated with mancozeb and tebuconazole prophylactically. If sanitation pruning is combined with regular applications of fungicides, disease can be combated.
AFRIKAANSE OPSOMMING: Mikrofungi wat tot die genus Botryosphaeria behoort, is heterotrofiese organismes, wat patogenies op houtagtige plante kan wees. Hulle veroorsaak ernstige, en in sommige gevalle, verwoestende verliese, deur blaarnekrose, stamkankers en plantafsterwing. Die Proteaceae snyblom-industrie in Suid-Afrika maak 70% van die nasionale snyblomindustrie uit. Botryosphaeria siektes is 'n belangrike struikelblok in die produksie en handeldryf van Proteaceae, en daar is 'n ernstige behoefte om die etiologie, epidemiologie en beheer van siektes te ondersoek. Verliese van een van die belangrikste proteas, P. magnifica, beloop plaaslik 50% of meer. Die hoof doelstellings van hierdie studie was dus om die etiologie en epidemiologie van Botryosphaeria stamkankers op P. magnifica en ander Proteaceae vas te stel en metodes van siektebeheer te ondersoek. Hoewel daar 'n wye hoeveelheid inligting rakende die swam bestaan, wat in Hoofstuk I hersien is, is daar relatief min inligting oor Botryosphaeria op Proteaceae beskikbaar. Die taksonomie van Botryosphaeria benodig deeglike hersiening, en molekulêre tegnieke word benodig om spesie-identiteite op te klaar. In Hoofstuk 2 is gevind dat Phyllachora proteae, 'n blaarpatogeen van proteas, 'n Fusicoccum anamorf produseer, wat as F. proteae beskryf word. 'n Sphaeropsis-agtige synanamorf is met F. proteae geassosieer en 'n nuwe kombinasie vir P. proteae is as B. proteae in Botryosphaeria voorgestel. Die taksonomie van Botryosphaeria is, beide op die genus- as die spesievlak, in wanorde. In Hoofstuk 3 word die taksonomiese geskiedenis van Botryosphaeria hersien, en die genus word omskryf en van ander morfologies soortgelyke genera onderskei. Hoewel verskeie anamorf genera al met Botryosphaeria op grond van morfologiese waarnemings en filogenetiese analise van ITS rDNA volgorde data verbind is, word twee anamorf genera nou herken, dié met gepigmenteerde konidia (Diplodia), en dié met deurskynende konidia (Fusicoccum). Botryosphaeria proteae moet dus van Botryosphaeria uitgesluit word. Verskeie patogeniese Botryosphaeria spp. het 'n endofitiese fase in hul lewenssiklus. Hulle word dus onwetend in ander lande ingevoer waar hulle 'n gevaar vir landbou en inheemse plantegroei kan inhou. Die huidige wêreldverspreiding van Botryosphaeria spp. wat met Proteaceae geassosieer word is opgeklaar, en in Hoofstuk 4 word 'n sleutel tot die taksa wat met Proteaceae geassosieer word verskaf. Vyf Botryosphaeria spp. word met snyblom Proteaceae wêreldwyd geassosieer, naamlik B. lutea, B. protearum, B. proteae, B. ribis en B. obtusa. B. protearum word as 'n nuwe spesie beskryf. 'n Deeglike kennis van siekte-epidemiologie is noodsaaklik ten einde verliese te verminder. In Hoofstuk 5 dui ek aan dat letsels wat lei tot stamkankers, veroorsaak deur Botryosphaeria protearum op P. magnifica, in die hoofnerf of rant van blare ontstaan. Koch se postulate is uitgevoer en daar is vasgestel dat die aantal letsels wat vanuit kunsmatige inokulasies ontwikkel het korreleer met die styselvlakke teenwoordig in die blare ten tye van die inokulasie. In Hoofstuk 6 word getoon dat B. protearum as 'n endofiet in die blare van P. magnifica. In natuurlike standplase van proteas is stamkankers skaars, maar in verboude plantasies is die voorkoms hoog. Voedingsanalises dui aan dat hoër vlakke van stikstof in die blare van verboude plante in die lente voorkom, wat siekte-ontwikkeling moontlik kan bevorder. Hoë vlakke van natrium in die blare van natuurlike plante mag siekteontwikkeling beperk. Die ernstige ekonomiese verliese wat deur B. protearum veroorsaak word, maak die soektog na verbeterde metodes van siektebeheer noodsaaklik. Fungisiedtoedienings maak 'n belangrike deel uit van 'n geïntegreerde benadering tot siektebeheer. In Hoofstuk 7 dui in vitro toetse aan dat tebuconazole, benomyl, prochloraz me, iprodione en fenarimol die miseliumgroei van B. protearum effektief verminder. 'n Vermindering van 25-85% is aangetoon in die voorkoms van stamkankers in die veld, deur die toediening van fungisiedes en sanitasiesnoei. Die beste beheer is verkry deur die voorkomende toediening van benomyl, bitertanol, fenarimol, iprodione en prochloraz manganese chloride, afgewissel met mancozeb en tebuconazole, op plante in die veld. Indien sanitasiesnoei met gereelde toedienings van fungisiedes gekombineer word, kan die siekte bekamp word.

Thesis (MSc)--Stellenbosch University, 2004.
ENGLISH ABSTRACT: This thesis consists of four chapters that present research findings on Colletotrichum diseases associated with Proteaceae worldwide. The first chapter is a review of literature regarding the taxonomy and histology of Colletotrichum species associated with Proteaceae. The literature is not restricted to Proteaceae hosts, as information regarding Colletotrichum on Proteaceae is very limited. In chapter two, Colletotrichum spp. associated with proteaceous hosts growing in various parts of the world were identified based on morphology, sequence data of the internal transcribed spacer region (ITS-I, ITS-2), the 5.8S gene, and partial sequences of the B-tubulin gene. Four species of Colletotrichum were associated with Proteaceae. Colletotrichum gloeosporioides was isolated from Protea cynaroides cultivated in South Africa and Zimbabwe and from a Leucospermum sp. in Portugal, but is known to occur worldwide on numerous hosts. A recently described species, C. boninense, was associated with Zimbabwean and Australian Proteaceae, but also occurred on a Eucalyptus sp. in South Africa. This represents a major geographical and host extension for the species, and a description of the African strains is provided. Colletotrichum crassipes was represented by a single isolate obtained from a Dryandra plant in Madeira. Colletotrichum acutatum was isolated from Protea and Leucadendron in South Africa as well as from other proteaceous hosts occurring elsewhere. Colletotrichum acutatum f. sp. hakea was isolated from Hakea in South Africa. In chapter three, pathogenicity of these Colletotrichum species to certain proteas was established, relative aggressiveness of the different species tested and host response to them were compared as well as the effect that wounding had on host response. From the results obtained it is concluded that C. acutatum and C. gloeosporioides are the primary pathogens associated with Colletotrichum leaf necrosis, and C. acutatum is the main cause of anthracnose and stem necrosis of Proteaceae in South Africa. A histological study was performed in chapter four in response to the findings from the previous chapter. The behaviour of two C. acutatum isolates (one originating from Protea and the other from Hakea, C. acuataum f.sp. hakea) was studied on inoculated Protea leaf surfaces using light and scanning electron microscopy. Colletotrichum acutatum from Protea formed melanised appressoria on the leaf surface, whereas C. acutatum from Hakea formed very low numbers of both melanised and unmelanised appressoria. Most of the appressoria formed by C. acutatum from Protea were formed on the cell junctions and on the periclinal walls of the epidermal cells. From this study it is clear that C. acutatum f. sp. hakea is not a pathogen of Protea. Consequently the current use of this isolate as a biological control agent of Hakea in South Africa poses no threat to indigenous Protea species. Colletotrichum acutatum from Protea (although closely related to C. acutatum f. sp. hakea), is a pathogen of Protea, which was confirmed by histological observations. In conclusion, the present study has shown that several species of Colletotrichum are associated with diseased Proteaceae. These species differed in their pathogenicity and aggressiveness when inoculated onto certain protea cultivars. These differences could be partially explained by examining the behaviour of C. acutatum on the leaf surface. It is clear, however, that the distribution of the different species, their aggressrveness on different Proteaceae and their modes of infection needs to be investigated further. This work provides a basis for future research on the long-term effective management of these pathogens in fynbos production.
AFRIKAANSE OPSOMMING: Hierdie tesis bestaan uit vier hoofstukke wat handeloor navorsing van Colletotrichum siektes van Proteaceae wêreldwyd. Die eerste hoofstuk is 'n oorsig van literatuur rakende die taksonomie en histologie van die Colletotrichum spesies wat met Proteaceae geassosieer word. Die literatuur oorsig is nie beperk tot die Proteaceae nie aangesien baie min inligting rakende Colletotrichum op Proteaceae bestaan. In die tweede hoofstuk word die Colletotrichum spesies wat met proteas in verskeie dele van die wêreld geassosieer word, op grond van morfologie, DNS volgorde data van die interne getranskribeerde spasieerder area ("ITS-I, ITS-2"), die 5.8S geen, en gedeeltelike DNS volgordes van die B-tubulin geen geïdentifiseer. Vier Colletotrichum spesies is met die Proteaceae geassosieer. Colletotrichum gloeosporioides is geïsoleer vanaf Protea cynaroides wat in Suid-Afrika en Zimbabwe gekweek is en vanaf 'n Leucospermum sp. in Portugal, maar is bekend op verskeie gashere wêreldwyd. 'n Spesie wat onlangs beskryf is, C. boninense, is met Zimbabwiese en Australiaanse Proteaceae geassosieer, maar kom ook op 'n Eucalyptus sp. in Suid-Afrika voor. Dit is 'n groot uitbreiding van die geografiese voorkoms en gasheerreeks van hierdie spesie en 'n beskrywing van die Afrikaanse rasse word gegee. Colletotrichum crassipes is verteenwoordig deur 'n enkele isolaat wat vanaf 'n Dryandra plant in Madeira verkry is. Colletotrichum acutatum is vanaf Protea en Leucadendron in Suid-Afrika asook vanaf ander proteas wat elders voorkom, geïsoleer. Colletotrichum acutatum f. sp. hakea is vanaf Hakea in Suid-Afrika geïsoleer. In hoofstuk drie is die patogenisiteit van hierdie Colletotrichum spesies teenoor sekere proteas getoets, die relatiewe aggressiwiteit van die verskillende spesies is vergelyk, asook die gasheer se reaksie teenoor die spesies en die effek wat verwonding op die gasheer gehad het. Daar kan afgelei word vanaf die resultate dat C. acutatum en C. gloeosporioides die primêre patogene is wat met Colletotrichum blaarnekrose geassosieer word, en dat C. acutatum die hoof oorsaak is van antraknose en lootnekrose van Proteaceae in Suid-Afrika. 'n Histologiese studie is in hoofstuk vier uitgevoer in reaksie op die bevindings van die vorige hoofstuk. Die gedrag van twee C. acutatum isolate (een vanaf Protea en die ander vanaf Hakea, C. acutatum f.sp. hakea) op die oppervlaktes van geïnokuleerde Protea blare is bestudeer deur gebruik te maak van lig- en skandeer-elektronmikroskopie. Colletotrichum acutatum vanaf Protea vorm gemelaniseerde appressoria op die blaaroppervlak, terwyl C. acutatum vanaf Hakea klein hoeveelhede van beide gemelaniseerde en ongemelaniseerde appressoria vorm. Meeste van die appressoria wat deur C. acutatum vanaf Protea gevorm word, vorm op die aanhegtingspunte tussen selle en op die periklinale wande van die epidermale selle. Vanuit hierdie studie is dit duidelik dat C. acutatum f. sp. hakea nie 'n patogeen van Protea is nie. Gevolglik hou die huidige gebruik van hierdie isolaat as biologiese beheer agent van Hakea in Suid-Afrika geen gevaar in vir inheemse Protea spesies nie. Colletotrichum acutatum vanaf Protea (alhoewel dit naverwant is aan C. acutatum f. sp. hakea) is 'n patogeen van Protea en hierdie stelling is ook bevestig deur histologiese waarnemmgs. Ter samevatting het hierdie studie getoon dat verskeie Colletotrichum spesies geassosieer word met siektes van Proteaceae. Hierdie spesies het van mekaar verskil rakende patogenisiteit en aggressiwiteit nadat hulle op sekere protea kultivars geïnokuleer is. Hierdie verskille kon gedeeltelik verklaar word deur die gedrag van C. acutatum op die blaaroppervlaktes van verskillende protea kultivars. Dit is duidelik dat die verspreiding van die verskillende spesies, hulle aggressiwiteit op verskillende Proteaceae en hul infeksie metodes verder ondersoek moet word. Hierdie studie verskaf 'n basis vir toekomstige navorsing rakende lang-termyn effektiewe bestuur van hierdie patogene in fynbos aanplantings.

The effects of intraspecific and interspecific competition, host plant, and prior host plant experience on fecundity, rate of oviposition and mortality of adults and larval survival of Delia radicum Bouche (Cabbage Maggot (CM)), D. antiqua Meigen (Onion Maggot (OM)), and D. platura Meigen (Seed Corn Maggot (SCM)), were studied on cabbage, onion and bean plants.
An optimum density for maximum fecundity per female was observed when the four experimental densities were compared. This optimum density was higher on host than on non-host plants. CM females were host specific and did not oviposit on non-host plants. Rates of oviposition and mortality over a 30-day period were calculated for each density. The rate of oviposition was slower at higher densities on host plants for CM, OM and SCM. The rate of mortality increased at the highest density for CM (cabbage), OM (bean) and SCM (cabbage), but remained unaffected for OM on onion and cabbage and for SCM on onion and bean, when densities were compared. For OM, a delay in the rate of oviposition and mortality on cabbage (non-host plant) when compared with onion (host plant), suggests that cabbage was not as readily accepted as an oviposition site. Interspecific competition experiments at six density ratio's of SCM:OM indicated increased fecundity, or an increase in the rate of oviposition for OM, at the lower densities when single and mixed species were compared. For SCM no effects on fecundity were recorded, but the rate of oviposition was slower and rate of mortality faster at the lowest density in the presence of OM. Similar studies with SCM and CM showed no such effects of competition.
Host plant exposure of SCM females during the pre-oviposition period resulted in a delay in initial acceptance of subsequent host plants as oviposition sites. This happened only when females were exposed to a secondary host during the pre-oviposition period. Once oviposition began, host discrimination ceased and a switch in oviposition sites to the preferred host did not alter the rate of oviposition. In CM, the rate of larval development increased at density 6 (optimum density). Above this density a decrease in the rate of development and a significant reduction in pupal weight was observed. Time required for fly emergence was not affected by increasing larval densities.

Thesis (PhD)--University of Stellenbosch, 2000.
ENGLISH ABSTRACT: The population density of the white wax scale, Ceroplastes destructor Newstead, has increased since 1994 in certain areas of Western and parts of Eastern Cape Provinces of South Africa where citrus is grown, particularly on Citrus reticulata (Blanco). A study was conducted to investigate its morphology, biology and ecology as contributions to the development of a sound integrated management programme. Characteristics of the immature stages and adult females were described and illustrated from field-collected and slide-mounted specimens. A key to the different stages and morphometeric characteristics useful for separating them are provided. No significant differences in female fecundity were found between orchards (P > 0.05). However, fecundity varied significantly between female size classes from the same orchard (P < 0.001). Female body-size also differed significantly between orchards (P < 0.05) and was significantly positively correlated with fecundity (P < 0.01). C. destructor has one discrete generation per year in South Africa. Oviposition commenced in November and continued through to the end of December with a few females ovipositing until mid January. Population density of the second instar peaked in February while the third instar extended from March to the end of July, followed by a peak population of adults in August. Seven primary and three secondary parasitoids, as well as four predator species attacking C. destructor were identified. Aprostocetus (= Tetrastichus) ceroplastae (Girault) was the dominant species, accounting for 78.87% of the total primary parasitoids reared. Peak numbers of parasitoids and predators were synchronized with peak emergence of susceptible scale stages, indicating that the host-parasitoid/predator system contained a density-dependent regulatory mechanism. Key mortality factors varied slightly between two of the orchards. Key stage mortality determined from a cohort life table was generally in the third instar (LIlI) and preovipositional female (POF) stage. Significant density-dependent mortality factors were demonstrated for the first instar (LI) and PDF stage. Dispersal of C. destructor is by first instar nymphs and the numbers caught on a series of yellow sticky traps varied significantly between crawler densities at the source, trap distances and trap directions from the source (P < 0.001). The numbers caught were positively correlated to the initial crawler density at the source (P < 0.01), suggesting that dispersal was density dependent. Trap distance and the numbers caught were inversely correlated (P < 0.01). Evaluation of effects of different densities of C. destructor on growth, survivorship and reproduction of scales as well as on leaf bearing ability of trees and area of leaf surface covered with sooty mould fungus was carried out on naturally infested Syzygium (= Eugenia) malaccensis (L.) plants. Scale body size and fecundity were inversely related to scale density (P < 0.01), suggesting density-dependent intraspecific competition. Scale survivorship generally declined with increasing density whereas scale parasitism and predation were positively correlated with density (P < 0.05). At high scale densities production of new leaves was significantly reduced (P < 0.01), reducing the resource base for subsequent generations of scale. Scale density and leaf area covered with sooty mould fungus were significantly positively correlated (P < 0.05). The toxicity of four synthetic insecticides against the three immature stages of C. destructor and of eight insecticides against the parasitoid A. ceroplastae was evaluated. Development of the first and second instars of C. destructor was completely arrested by the chemicals. Female fecundity, fertility and body sizes of survivors of treatments applied at the LIII stage were not significantly affected by any of the chemicals (P > 0.05). All the chemicals exhibited high toxicity to A. ceroplastae and hence are not recommended for integrated management of C. destructor in citrus orchards where A. ceroplastae plays an important role.
AFRIKAANSE OPSOMMING: Die populasiedigtheid van die witwasdopluis, Ceroplastes destructor Newstead, het sedert 1994 toegeneem in sekere gebiede van die Weskaap en Ooskaap provinsies van Suid-Afrika waar sitrus verbou word, veralop Citrus reticulata (Blanco). 'n Studie van hierdie insek se morfologie, biologie en ekologie is onderneem as bydrae tot die ontwikkeling van 'n geïntegreerde bestuursprogram. Die karaktertrekke van die onvolwasse stadia en die volwasse wyfies is beskryf en geïllustreer vanaf eksemplare wat in die veld versamel is en op g1asplaatjies gemonteer is. 'n Sleutel vir die verskillende stadia en morfometriese kenmerke wat nuttig is om hulle te onderskei, word voorsien. Geen beduidende verskille in die vrugbaarheid van wyfies van verskillende boorde is gevind nie (P < 0.05). Vrugbaarheid het egter betekenisvol verskil by die verskillende grootteklasse van wyfies uit dieselfde boord (P < 0.001). Die liggaamsgrootte van wyfies uit verskillende boorde het betekenisvol verskil (P < 0.05) en was betekenisvol positief gekorreleer met vrugbaarheid (P < 0.01). C. destructor het een generasie per jaar in Suid-Afrika. Eierlegging het in November begin en aangehou tot aan die einde van Desember, met enkele wyfies wat nog tot in middel Januarie eiers gelê het. Die populasiedigtheid van die tweede instar het 'n hoogtepunt in Februarie bereik, terwyl die derde instar van Maart tot aan die einde van Julie geduur het, gevolg deur 'n piekbevolking van volwassenes in Augustus. Sewe primêre en drie sekondêre parasitoïde asook vier predator spesies wat C destructor aanval, is geïdentifiseer. Aprostocetus (=Tetrastichus) ceroplastae (Girault) was die dominante spesies wat 78.87% van die totale aantal primêre parasitoïde wat uitgeteel is, uitgemaak het. Die pieke in die getalle van parasitoïde en predatore was gesinchroniseer met pieke in die verskyning van die gevoelige stadia, wat dui op die aanwesigheid van 'n digtheidsafhanklike regulatoriese meganisme. Die sleutel mortaliteitsfaktore het effens gevarieer tussen twee van die boorde. Die sleutelstadium van mortaliteit, soos bepaal m.b.v. 'n kohort lewenstabel, was gewoonlik die derde instar (LIlI) en die preoviposisionele wyfie (POW). Betekenisvolle digtheidsafhanklike mortaliteitsfaktore IS aangetoon vir die eerste instar (LI) en die POW. Die verspreiding van C.destructor vind plaas deur die eerste instar nimfe en die getalle wat op 'n reeks van taai geel valle gevang is, het betekenisvol gewissel volgens kruiperdigthede by die bron, asook die afstand en rigting van die valle vanaf die bron (P < 0.001). Die getalle wat gevang is, was positief gekorreleer met die aanvanklike kruiperdigtheid by die bron (P < 0.01), wat daarop dui dat verspreiding digtheidsafhanklik was. Die afstand van die valle en die aantal wat gevang is, was omgekeerd gekorreleer (P < 0.01). 'n Evaluering van die invloed van verskillende digthede van C. destructor op die groei, oorlewing en reproduksie van dopluise, asook die vermoë van bome om blare te dra en die area van die blaaroppervlak wat met roetskimmel besmet is, is uitgevoer op plante van Syzygium (= Eugenia) malaccensis (L.) met 'n natuurlike besmetting. Die liggaamsgrootte en vrugbaarheid van die dopluise was omgekeerd gekorreleer met hulle digtheid (P < 0.01), wat dui op digtheidsafhanklike intraspesifieke kompetisie. Die oorlewing van die dopluise het oor die algemeen afgeneem met toenemende digtheid, terwyl parasitisme en predasie positief gekorreleer was met digtheid (P < 0.05). By hoë dopluisdigthede het die produksie van nuwe blare betekenisvol afgeneem (P < 0.01), wat die hulpbronbasis vir daaropvolgende generasies van dopluise verswak. Die dopluisdigtheid en blaaroppervlak wat met roetskimmel bedek was, was positief gekorreleer (P < 0.05). Die toksisiteit van vier sintetiese insektemiddels teenoor die drie onvolwasse stadia van C. destructor en van agt insektemiddels teenoor die parasitoïd A. ceroplastae is geëvalueer. Die ontwikkeling van die eerste en tweede instars van C. destructor is heeltemal stopgesit deur die middels. Die fekunditeit, fertiliteit en liggaamsgrootte van wyfies wat toedienings op die LIIl stadium oorleef het, is nie betekenisvol ge-affekteer deur enige van die middels nie (P < 0.05). Al die middels was baie toksies teenoor A. ceroplastae en word dus nie aanbeveel vir die geïntegreerde bestuur van C. destructor waar A. ceroplastae 'n belangrike rol speel nie.

A new disease affecting potatoes was first detected in Mexico in 1993. Affected plants had aerial symptoms similar to those caused by potato purple top and psyllid yellows, but tubers had internal brown discoloration when sliced and dark stripes and streaks when processed to produce potato chips. The disease has been found in many potato production areas in Guatemala, Mexico, Honduras, New Zealand and the United States. The disease, termed Zebra Chip (ZC), has been associated with the presence of heavy infestations of the potato-tomato psyllid (Bactericera cockerelli). In 2009, a research group in New Zealand discovered that a new disease in tomato and pepper plants was caused by Candidatus Liberibacter solanacearum (Lso) and subsequently this same bacterium was associated with ZC in potato samples from Texas. The objectives of this study were: to assess the accumulation of Lso in various potato organs, to determine the effect of plant age on detection of Lso, symptom development and plant death, and (iii) to determine the effect of phosphorous acid on the development of ZC. Results from these studies showed significant differences in Lso populations between above and below ground tissues of the potato plant, with Lso populations in stolons and tubers being three to four times higher than those of leaf tissue and over seventy times greater than in stems. Time for detection of Lso by PCR in potato leaves of different ages at the time of inoculation ranged from 21 to 26 days after inoculation, symptoms development took 23 to 36 days. Plant death, took 24 to 47 days in plants of different age groups at the time of inoculation. In plants 15 weeks old at the time of inoculation, Lso was detected after 14 days in one plant out of 18; in plants 16 weeks old at the time of inoculation, Lso was detected after seven days in two plants out of 18. Phosphorous acid applications had no effect on the populations of Lso in potato tubers, onset of symptoms or plant death. All tubers showed ZC symptoms, making them unacceptable for the market.
North Dakota State University. Department of Plant Pathology

Soybean (Glycine max [L.] Merr.) is one of the most important crops in the world. The average annual yield losses due to soybean diseases and pests are estimated to be around 11% in the United States. Soybean yield losses due to sudden death syndrome (SDS), caused by the fungus Fusarium virguliforme O'Donnell & T. Aoki have been problematic in majority of the soybean producing states. In recent years, reniform nematode (RN, Rotylenchulus reniformis Linford and Oliveira) and frogeye leaf spot (FLS), caused by the fungus Cercospora sojina K. Hara have emerged as a major problem in the southern soybean producing states. Planting resistant cultivars is one of the most cost-efficient methods in managing SDS, RN, and FLS, therefore it would be critical to identify and map the quantitative trait loci (QTL) that underlie their resistances. Two soybean populations were evaluated in this study. The ‘Essex’ × ‘Forrest’ 77 near-isogenic lines were screened in the field to evaluate the disease index of SDS. The Essex × Forrest and ‘Flyer’ × ‘Hartwig’ recombinant inbred lines were screened in the greenhouse to assess the reproduction index of RN and the disease severity of FLS. The BARCSoySNP6k chip was used to genotype the two populations. Four QTL that underlie SDS resistances were mapped in the same region as Rfv06-01, Rfv06-02, Rfv13-01, and Rfv19-01. The Rfv06-02 interval in this study was smaller than the one previously reported. Rrr08-01, Rrr13-01, Rrr15-01, Rrr18-01, and Rrr18-02 were reported to confer resistances to RN. Rrr08-01, Rrr13-01 and Rrr15-01 were novel whereas Rrr18-01, and Rrr18-02 were mapped in previous studies. cqSCN-001 (soybean cyst nematode, Heterodera glycines Ichinohe) was identified in the same region as Rrr18-01, and Rrr18-02 whereas cqSCN-006 was identified in the same region as Rrr15-01. These findings provide further evidence that there are common sources of genetic resistances to RN and SCN. Rcs15-01 and Rcs15-02 were reported to confer resistances to FLS. Rcs15-01 was novel and Rcs15-02 was mapped at the same region as an Rcs mapped in a previous study. This indicated that Rcs15-02 has dual resistances to C. sojina races. Candidate genes were inferred in this study. The QTL mapped in this study could potentially be used in soybean breeding programs that aim to introgress genetic resources that confer resistances to SDS, RN, and FLS.

Bibliography: pages 175-184.
The occurrence of maize dwarf mosaic virus (MDMV) in field grown maize was investigated. For this purpose, maize showing mosiac symptoms was collected from different maize growing areas in South Africa by Prof. M.B. von Wechmar. These samples from Transvaal, Orange Free State and Natal were then investigated for the presence of MDMV and possible strains of this virus. Three virus isolates were purified and partially characterised. These isolates were serologically compared together with a fourth isolate SCMV 4975, obtained from the U.S., to establish strain relationships.

Germinating uredospores of race C17 of Puccinia graminis f.sp. tritici form characteristic infection structures (appressorium, infection peg, vesicle, infection hypha) in response to a 1.5 h heat shock at 29° C administered 2 h after germination at 19° C. The proportion of sporelings forming infection structures was augmented by nutrients, n-nonyl alcohol and, an appropriately timed heat shock. The heat shock temperature required to induce maximum differentiation had a very precise optimum which varied slightly for each spore lot. Variations one degree above or below this optimum reduced the percent differentiation by greater than 40%. The presence of an inhibitor of protein synthesis, puromycin, in the germination medium: (1) prevented uredosporeling differentiation but had no effect on germination, (2) significantly reduced the proportion of germtubes forming appressoria, and (3) in most cases prevented the division of germtube nuclei. It was concluded that essential differentiation-specific proteins are synthesized from the onset of germination, throughout the formation of appressoria and to the completion of differentiation. These results were consistent with the observed effects of heat shock on the rate of protein hydrolysis. During germination there was a net hydrolysis of protein leading to an increase in size of the endogenous pool of free amino acids and to an increased leakage of amino acids to the germination medium. Heat shock effectively reduced the amount of endogenous free amino acids and the extent to which amino acids were lost to the medium. It was concluded that in heat shocked sporelings protein synthesis was increased relative to protein hydrolysis by comparison with the relative rates of these two processes in germinating (non-shocked) uredosporelings. Moreover, there was no net protein synthesis during the formation of infection structures induced by heat shock. The loss of amino acids to the germination medium was selective, particularly in heat shocked sporelings.
Land and Food Systems, Faculty of
Graduate

Field experiments were conducted in two different growing environments to evaluate the spread and movement of Dickeya dadantii. A procedure to inoculate seed potatoes with Dickeya dadantii was developed to use during this study. Spread of Dickeya dadantii from inoculated potato seed to healthy potato seed during the handling, cutting and planting procedures was not detected at either location. Spread of Dickeya dadantii from inoculated seed to surrounding progeny tubers in the field was documented in both locations. In Florida, 33% of progeny tubers tested positive for Dickeya using PCR, and in North Dakota, 13% of the progeny tubers tested positive. Stunting was observed in plants grown from Dickeya dadantii inoculated seed tubers in North Dakota, but not in Florida. These results indicate that Dickeya dadantii may spread during the seed handling and cutting processes and can spread in the field from infected seed tubers to progeny tubers.

Studies presented in this dissertation highlight the importance of fungal pathogens in forestry nurseries in South Africa. Both Acacia meamsii seedlings and Eucalyptus hybrid cuttings are shown to be affected by important nursery pathogens. Chapter one presents an evaluation of the potential importance of pathogens to Eucalyptus hedge plants maintained in hydroponics. Hydroponics is a new technology being used in South African forest nurseries, which allows for the rapid establishment of Eucalyptus hedge plants. However, no information is available on pathogens affecting Eucalyptus in hydroponics. By applying information on pathogens of other hydroponic crops, several potentially important pathogens were identified and these reside in the genera Phytophthora, Pythium and Fusarium. Possible disease symptoms in Eucalyptus caused by these pathogens include wilting, stem cankers and root rots. Implementation of appropriate control measures that include cultural, biological and chemical practices could prevent and/or reduce disease impact in hydroponics. Chapter two presents the results of a survey of the roots of Eucalyptus hedge plants grown in an ebb and flow hydroponic system. An interesting result of the survey was the discovery of Cylindrocladium pauciramosum in the hydroponic system. This is the first report of the pathogen in a hydroponic system. Other important pathogens in the genera Phytophthora and Pythium were also isolated. Two Pythium species, namely P. dissotocum and P. helicoids, found in the roots and nutrient solution are new to Eucalyptus. Several Fusarium species were also isolated of which two, namely F. nygamai and F. lateritium, are also new to Eucalyptus. Chapter three of this dissertation presents the results of a survey of Eucalyptus cuttings conducted at four forestry nurseries in KwaZulu-Natal, South Africa. Several well-known Eucalyptus nursery pathogens were isolated. Cylindrocladium pauciramosum was identified as the dominant pathogen on Eucalyptus cuttings. This was confirmed based on morphological characteristics and DNA sequence comparisons. Pathogenicity tests conducted using a spore suspension of C. pauciramosum indicated that this pathogen is capable of infecting most commercial Eucalyptus clones used in South Africa. Chapter four considers a serious disease of Acacia mearnsii seedlings caused by an unidentified species of Cylindrocladium. Cylindrocladium pauciramosum was isolated from A. mearnsii seedlings showing girdling and stem canker symptoms. The pathogen was identified based on morphological characteristics and DNA sequence comparisons. Pathogenicity tests with Acacia seedlings confirmed the susceptibility of this tree to C. pauciramosum infection. This dissertation clearly indicates that Cylindrocladium pauciramosum is an important nursery pathogen in South African forestry nurseries. This pathogen has already been shown to be limiting during production of planting stock. I hope to have highlighted the importance of C. pauciramosum and other nursery pathogens in forestry nurseries in South Africa. This study will also hopefully provide information to forestry nursery managers and help them improve production.
Dissertation (MSc)--University of Pretoria, 2004.
Microbiology and Plant Pathology
Unrestricted

White mold caused by Sclerotinia sclerotiorum attacks a wide host range of broad-leafed plants which includes potatoes. Current control is limited to the use of chemicals, but biological control has emerged as an eco-friendly alternative. For the study, 19 bacterial strains and 18 fungal strains obtained from soil samples taken from a potato field naturally infested with the pathogen S. sclerotiorum were tested for the effects on S. sclerotiorum mycelium growth and sclerotia viability in vitro. A total of eight bacterial strains and six fungal strains proved to be effective in the inhibition of S. sclerotiorum mycelium growth on PDA plate using a dual culture technique. These antagonistic microbes were six Bacillus subtilis, Bacillus pumilis, Bacillus marisflavi, Fusarium solani, Fusarium equiseti, Fusarium chlamydosporum, Aspergillus niger, Aspergillus insuetus and Penicillium citrinum. There was a significant difference (p<0.05) in the interaction between S. sclerotiorum mycelium growth and the time after inoculation with a S. sclerotiorum mycelium plug for both bacterial and fungal soil isolates. An additional sclerotia viability test was carried out using four of the eight antagonistic bacteria, and six of the antagonistic fungi. The results showed that two Bacillus species, namely B. pumilis and B. marisflavi can effectively reduce sclerotia viability. The other two bacteria (both B. subtilis), recorded low percentage reduction in sclerotia viability. As for the six antagonistic fungi, the viability test proved to be less effective in determining sclerotia viability. However, the result of this study supports the use of bio-control agents, not only because they are environmentally friendly, but because they are also an effective way of controlling the plant pathogen, S. sclerotiorum.

Rattus sordidus (canefield rat) is a major pest in north Queensland sugarcane growing areas, causing losses of between $2 and $4 million each year. A further $0.2 to $0.4 million is expended on annual baiting campaigns. This procedure provides only short-term results, is seldom cost-effective and is hazardous to non-target species and the environment. There was a close relationship between the dynamics of R. sordidus populations and the crop cycle. During the 1987/88 crop cycle, breeding occurred over the January- July period and coincided with the period when summergrasses were abundant in crops and the predominant food source of R. sordidus. The relationship between the onset of breeding, the first appearance of summergrasses and diet of R. sordidus indicates that breeding is dependent on the availability of a non-cane food source. The level of in-crop weed biomass may therefore play an important role in the regulation of population and damage levels throughout a district. Consequently, a number of agricultural practices which affect in-crop weed levels may have a significant effect on R. sordidus populations. The practice of green cane harvest and trash-blanketing has increased in most northern sugarcane growing districts since the early 1980's. This practice differs to the conventional technique in that crops are not burnt prior to harvest and following harvest the trash, comprising the green "tops" and dry leaf material, is left as a "trash-blanket" on the ground and minimum or zero tillage techniques employed. Suppression of weed germination and growth is a major agronomic advantage associated with this technique. In-crop weed control may also be achieved through the application of herbicides. The monetary benefit associated with yield increases as a result of reduced weed competition in young crops has lead to an increase in the number of crops treated with herbicide. This study investigated the effect of green cane harvesting and trashblanketing, the conventional agricultural practice and herbicide applications on the dynamics of R. sordidus populations during the 1987/88 crop cycle.

False codling moth is a known pest of economic importance to many cultivated crops in South Africa and Africa south of the Sahara, and is particularly severe on citrus. If the fruit is infested just before harvest the chances of detecting signs of infestation are very low. As a result, the risk of packaging infested fruit and exporting them as healthy fruit is high. It is therefore a priority to develop a post-harvest technique for detection of False codling moth in citrus fruit at different levels of infestation in order to reduce phytosanitary risk. Compounds released and detected were indicative of infestation and were not insect produced but naturally produced fruit volatiles emitted at higher levels as a result of the insect within the fruit. Five major volatile compounds of interest were released by the infested oranges. These major volatile compounds include D-limonene, 3,7-dimethyl-1,3,6-octatriene, (E)-4,8-dimethyl-1,3,7-nonatriene, caryophyllene and naphthalene. Limonene was one of the most abundant volatile compounds released by the infested citrus fruit. Naphthalene, which is possibly produced due to larval feeding and development within the fruit maintained higher concentrations than controls throughout the infestation within the fruit. Naphthalene would be a good indicator of False codling moth infestation, however, not primarily for early infestation detection. A significantly higher concentration of D-limonene, 3,7-dimethyl-1,3,6-octatriene, (E)-4,8-dimethyl-1,3,7-nonatriene and naphthalene was detected using the SEP over the SPME technique. The application of an SPME procedure and the utilization of this method for detection of volatiles present in the headspace of intact infested fruit are evaluated and the possible volatile compounds diagnostic of Thaumatotibia leucotreta infestation of orange fruit and differences in volatile compound response in different orange varieties is discussed.

Thesis (MscAgric (Horticulture))--University of Stellenbosch, 2005.
The occurrence of both pre- and postharvest leaf blackening in certain Protea species and cultivars is a problem that severely limits their marketability, vase life and transport options. This research focuses on : (I) The distribution of carbohydrates in inflorescence bearing stems of certain Protea cultivars from harvest, following pulsing with a 10 g.L-1 glucose solution until four weeks postharvest. Stems were held under a variety of postharvest conditions, and (II) The suppression of Protea postharvest leaf blackening with specific focus on the cultivar ‘Sylvia’ (P. eximia x P. susannae).

12 pp.
plant disease bulletins; July 2006 original publishing date, rev. 10/08
Cacti, agaves and yuccas are classified as succulents, plants that have highly specialized anatomical features such as thick waxy cuticles, fleshy or minimal leaves, modified leaves (spines), and roots with extra storage capabilities for food and water. These modifications allow them to survive and thrive in harsh desert environments. They survive long periods of drought in areas of sparse rainfall and intense heat. During stressful periods, many succulents cease to grow, drop unnecessary leaves, dehydrate and become dormant until conditions for growth return. Despite their adaptations, succulents suffer from diseases, insect pests and cultural problems. Some of the more common problems that occur in cacti, agave and yuccas in Arizona are discussed in this bulletin.

Thesis (MSc)--Stellenbosch University, 2015.
ENGLISH ABSTRACT: The codling moth, Cydia pomonella (Lepidoptera: Tortricidae), is the key pest of apples and pears worldwide. The withdrawal of certain fundamental chemicals from codling moth management spray programmes, due to concerns about human, environmental and ecosystem health, has resulted in the search for softer, more environmentally friendly, and safer control measures. Entomopathogenic nematodes (EPNs), naturally occur in the soil, and actively search for hosts. The interest in using EPNs from the families Heterorhabditidae and Steinernematidae as a control measure was sparked in 1953, when an EPN was discovered in an insect. The aim is to incorporate EPNs in an integrated pest management (IPM) programme, to ensure minimal residue and eventually residue-free pome fruit production in South Africa. In order to ensure EPN success, both the environmental and technical factors influencing their efficacy, were investigated in this study. The biocontrol potential of three imported EPN isolates, being Steinernema feltiae and two isolates of Heterorhabditis bacteriophora (Hb1, Hb2), as well as a local isolate, Steinernema yirgalemense, were evaluated for the control of the codling moth under local conditions. All concentrations of S. yirgalemense, applied by immersion in a suspension of nematodes, gave > 98% control. The two formulated isolates of H. bacteriophora, Hb1-f and Hb2-f, gave < 30% control. When using the same nematode isolates, produced in vivo, S. yirgalemense still resulted in a higher codling moth control of > 90%, compared to 54% and 31% control of the H. bacteriophora Hb1 and Hb2 isolates, respectively. In follow up field trials, S. feltiae resulted in ≥ 80% control, and was thus more effective than both S. yirgalemense and the H. bacteriophora (Hb1) isolates, with 66% and 24%, and 24% and 9% control, for two separate trials, respectively. To validate the data obtained from the field trials, subsequent laboratory bioassays were conducted evaluating temperature regimes, following the same cycle as under natural conditions, with a constant humidity of 100%. Steinernema feltiae proved to be most effective, causing > 90% mortality, followed by S. yirgalemense, with 78% mortality. The two H. bacteriophora isolates (Hb1, Hb2) under the above-mentioned laboratory conditions, resulted in 73% and 59% control, respectively. Humidity thus seems to be the most important factor affecting EPN efficacy during above-ground applications. Steinernema feltiae proved to be a better candidate than S. yirgalemense for the control of the codling moth. The efficacy of different EPN isolates in controlling diapausing codling moth larvae at different temperatures was also evaluated, under local conditions, using spray application. Steinernema feltiae and two isolates of H. bacteriophora Hb1 and Hb2, including two local isolates, S. yirgalemense and Steinernema jeffreyense, were evaluated. The use of S. jeffreyense resulted in the most effective control, with 67% mortality, followed by H. bacteriophora (Hb1) with 42%, and then by S. yirgalemense with 41%. Laboratory bioassays simulating field conditions revealed that S. feltiae was most virulent to codling moth larvae, with 67% mortality by infection, followed by S. yirgalemense with 58%, the H. bacteriophora strain Hb1 with 48%, and the Hb2 strain with 24%. A comparison of the infection and penetration rate of two isolates of H. bacteriophora (Hb1, Hb2), S. feltiae and S. yirgalemense, which was carried out in multiwell plates at 14°C and 25°C, respectively, confirms the dramatic effect of temperature on EPN efficacy. At 14°C, all treatments with EPN species resulted in slower codling moth mortality than they did at 25°C, as after 48 h, < 15% mortality was recorded for all species, whereas at the warmer temperature, > 98% mortality was recorded for all species. After the exposure of washed, cool-treated larvae to 25°C for 24 h, the application of both S. feltiae and S. yirgalemense resulted in 100% mortality, whereas the application of the two H. bacteriophora isolates, Hb1 and Hb2, resulted in 68% and 54% control, respectively, over the same time period. At 14°C, S. feltiae had the highest average penetration rate of 20 IJs/insect, followed by S. yirgalemense with 14 IJs/insect, whereas S. yirgalemense had the highest penetration rate at 25°C, with 39 IJs/insect, followed by S. feltiae, with 9 IJs/insect. The two H. bacteriophora isolates had higher average penetration rates at the higher temperature. This study has highlighted the biocontrol potential of S. jeffreyense, as well as showing that S. feltiae is a cold-active nematode, whereas the other three EPN isolates prefer warmer temperatures. Stacked wooden fruit bins are regarded as preferred overwintering sites for codling moth diapausing larvae. Control strategies against the codling moth in South Africa have been hampered by the reinfestation of orchards by nearby stacked infested fruit bins or by the movement of bins between orchards. Worldwide, wooden fruit bins are systematically being replaced with plastic bins, which, in South Africa, will only be phased out over a few years. The objective of this study was to evaluate the potential of H. bacteriophora, S. feltiae, and S. yirgalemense, to disinfest miniature wooden fruit bins under controlled conditions in the laboratory. After dipping minibins in a suspension of 25 IJs/ml of all three EPN species, under optimum conditions of temperature and humidity, the highest percentage of control was obtained using S. feltiae (75%) followed by S. yirgalemense (57%), and then by H. bacteriophora (Hb1) (27%). The addition of adjuvants significantly increased (p < 0.001) S. feltiae infectivity to > 95%, whereas it did not result in a significant increase in H. bacteriophora or S. yirgalemense infectivity. The results indicated that H. bacteriophora would not be a suitable candidate to use for the control of the codling moth larvae in wooden fruit bins. The current preferred candidate for control would be S. feltiae, whose efficacy could be increased by means of the addition of an adjuvant. During winter, when the whole codling moth population are larvae and in diapause, no control measures are applied in orchards. This study has shown that EPNs can be sprayed in orchards to lower the codling moth cohort emerging after winter, as well as be included in an IPM programme. EPNs can act as a second line of defence, through supplementary control, and ensure effective control of the codling moth larvae which survived chemical spray applications, to safeguard against resistant codling moth populations in the next season.
AFRIKAANSE OPSOMMING: Kodlingmot, Cydia pomonella (Lepidoptera: Tortricidae), is ‘n belangrike plaag van appels en pere wêreldwyd. Die onttrekking van sekere fundamentele chemikalieë vanuit die kodlingmot beheerprogram weens die kommer oor menslike, omgewings en ekosisteemgesondheid, het gelei tot die soektog na sagter, meer omgewingsvriendelike en veiliger beheermaatreëls. Entomopatogeniese nematodes (EPNs) kom natuurlik in die grond voor en soek aktief na gashere. Die belangstelling in die gebruik van EPNs van die families Heterorhabditidae en Steinernematidae as 'n beheermaatreël is te danke aan die ontdekking van 'n EPN in ‘n insek in 1953. Die doel is om EPNs in 'n geïntegreerde plaagbeheerprogram (GPB) te inkorporeer om sodoende minimale residue te verseker en uiteindelik residu vrye produksie van kernvrugte in Suid-Afrika. Ten einde die sukses van EPNs te verseker, is beide die omgewings- en tegniese faktore wat hul doeltreffendheid beïnvloed in die studie ondersoek. Die biologiese beheer potensiaal van drie ingevoerde EPN isolate, Steinernema feltiae en twee Heterorhabditis bacteriophora (Hb1, Hb2) isolate, sowel as 'n plaaslike isolaat, Steinernema yirgalemense, is vir die beheer van kodlingmot onder plaaslike toestande geëvalueer. Alle konsentrasies van S. yirgalemense, wat deur indompeling in ‘n suspensie van nematodes toegedien is, het > 98% beheer tot gevolg gehad. Die twee geformuleerde isolate van H. bacteriophora, Hb1-f en Hb2-f, het < 30% beheer gegee. Met die gebruik van dieselfde nematode isolate, wat in vivo geproduseer is, het S. yirgalemense nog steeds 'n hoër kodlingmot beheer van > 90% opgelewer, in vergelyking met die 54% en 31% beheer van die H. bacteriophora Hb1 en Hb2 isolate, onderskeidelik. Steinernema feltiae het in opvolg veldproewe ≥ 80% beheer tot gevolg gehad en was dus meer effektief as beide S. yirgalemense en die H. bacteriophora (Hb1) isolate, met 66% en 24% en 24% en 9% beheer onderskeidelik in twee afsonderlike veldproewe. Om die resultate van die veldproewe te bevestig, is daaropvolgende laboratorium biotoetse uitgevoer en temperatuur regimes is geëvalueer deur die selfde siklus as onder natuurlike toestande te volg, met 'n konstante humiditeit van 100%. Die studie het bewys dat S. feltiae die mees doeltreffende isolate was met > 90% mortaliteit, S. yirgalemense het gevolg met 78% mortaliteit. Die twee H. bacteriophora isolate (Hb1, Hb2) het onderskeidelik onder bogenoemde laboratorium toestande 73% en 59% beheer tot gevolg gehad. Humiditeit blyk dus die belangrikste faktor te wees wat EPN se doeltreffendheid tydens bogrondse toediening affekteer. Die studie het bewys dat S. feltiae 'n beter kandidaat as S. yirgalemense vir die beheer van kodlingmot is. Die doeltreffendheid van verskillende EPN isolate vir die beheer van diapause kodlingmot larwes sowel as EPN se aktiwiteit by verskillende temperature is ook onder plaaslike toestande, deur bogrondse bespuitings, geëvalueer. Steinernema feltiae en twee isolate van H. bacteriophora (Hb1, Hb2), S. yirgalemense en ‘n ander plaaslike isolaat, Steinernema jeffreyense, is geëvalueer. Die gebruik van S. jeffreyense, het tot die mees effektiewe beheer gelei, met 67% mortaliteit, gevolg deur H. bacteriophora (Hb1) met 42%, en dan S. yirgalemense met 41%. Laboratorium biotoetse wat veldtoestande simuleer, het bewys dat S. feltiae die mees doeltreffend teen kodlingmot larwes is, met 67% mortaliteit tydens infeksie, gevolg deur S. yirgalemense met 58%, die H. bacteriophora Hb1 isolaat met 48%, en die Hb2 isolaat met 24%. 'n Vergelyking van die infeksie- en penetrasie tempo van twee isolate van H. bacteriophora (Hb1, Hb2), S. feltiae en S. yirgalemense wat in 12-put plate teen 14°C en 25°C uitgevoer is, het die dramatiese effek van temperatuur op EPN doeltreffendheid bevestig. By 14°C het alle EPN spesies behandelings stadiger kodlingmot mortaliteit as by 25°C na 48h tot gevolg gehad. ‘n Mortaliteit van < 15% is vir alle spesies aangeteken terwyl by die warmer temperature is > 98% mortaliteit vir alle spesies aangeteken. Na die blootstelling van afgespoelde, koel behandelde larwes aan 25°C vir 24 uur, het die toediening van beide S. feltiae en S. yirgalemense, 100% mortaliteit van larwes tot gevolg gehad terwyl die toediening van die twee H. bacteriophora isolate, Hb1 en Hb2, onderskeidelik 68% en 54% beheer tot gevolg gehad, oor dieselfde tydperk. By 14°C, het S. feltiae die hoogste gemiddelde penetrasie tempo van 20 ILs/ larwe, gevolg deur S. yirgalemense met 14 ILs/ larwe tot gevolg gehad, terwyl S. yirgalemense die hoogste penetrasie tempo getoon het by 25°C met 39 ILs/ insek, gevolg deur S. feltiae met 9 ILs/ insek. Die twee H. bacteriophora isolate (Hb1 en Hb2) het ook hoër gemiddelde penetrasie tempo by die hoër temperatuur getoon. Hierdie studie het die biobeheer potensiaal van S. jeffreyense beklemtoon, asook weereens bevestig dat S. feltiae ‘n koue-aktiewe nematode is, terwyl die ander drie EPN isolate warmer temperature verkies. Hout vrugtekratstapels, word beskou as ‘n ideale oorwintering skuiling vir kodlingmot diapause larwes. In Suid-Afrika word beheerstrategieë teen kodlingmot in die wiele gery deur die herbesmetting van boorde deur nabygeleë besmette hout vrugtekratte of deur die beweging van kratte tussen boorde. Hout vrugtekratte word wêreldwyd stelselmatig vervang met plastiek kratte. Dit sal egter eers oor ‘n aantal jare in Suid-Afrika uitgefaseer word. Die doel van hierdie studie was om die potensiaal van H. bacteriophora, S. feltiae, en S. yirgalemense te evalueer deur miniatuur hout vrugtekratte onder gekontroleerde toestande in die laboratorium te disinfekteer. Na die onderdompeling van die mini vrugtekratte in 'n nematode suspensie van 25 ILs/ml van al drie EPN spesies, onder optimale toestande van temperatuur en humiditeit, is die hoogste persentasie van beheer met die gebruik van S. feltiae (74,85% ± 3.64%) verkry. Die byvoeging van toevoegings middels het S. feltiae se vermoë om te infekteer betekenisvol (p <0,001) tot > 95% verhoog, maar dit het nie tot 'n betekenisvolle toename in die infektiwiteit van H. bacteriophora of S. yirgalemense gelei nie. Die resultate dui daarop dat H. bacteriophora nie 'n geskikte kandidaat is om te gebruik vir die beheer van kodlingmot larwes in besmette hout kratte nie. Die voorkeurkandidaat tans vir beheer is S. feltiae, waarvan die doeltreffendheid verhoog kan word deur middel van die byvoeging van 'n bymiddel. Gedurende die winter wanneer die hele kodlingmot populasie as larwes in diapause is, word geen beheer in boorde toegepas nie. Hierdie studie het getoon dat EPNs in boorde gespuit kan word om sodoende die opkomende kodlingmot populasie na die winter te verlaag en kan ook ingesluit word in 'n GPB program. Die EPNs kan as 'n tweede verdedigingslinie optree en doeltreffende beheer van kodlingmot larwes verseker wat chemiese bespuitings oorleef het, en sodoende beskerming teen weerstandige kodlingmot populasies in die volgende seisoen bied.

In this study, surveys were conducted in pea and potato fields in North Dakota and Central Minnesota to investigate the incidence and abundance of plant-parasitic nematodes in these fields. Moreover, the effect of the pin nematode, Paratylenchus nanus, on plant growth and yield of six field pea cultivars was determined under greenhouse conditions. Similarly, the influence of lesion nematode, Pratylenchus penetrans, and wilt fungi, Fusarium oxysporum alone and together on growth and yield of potato cultivar ‘Red Norland’, was evaluated in microplots under field conditions. The results indicate Paratylenchus spp. and Pratylenchus spp. are the most frequent nematodes, respectively, in pea and potato fields. Pin nematodes reproduced on field pea cultivars and caused up to 37% reduction in plant height and 40% reduction in yield. Additionally, both P. penetrans and F. oxysporum alone, and together had significant negative effect on growth and yield of potato.

Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most important foliar disease of sugar beet worldwide. Control strategies for CLS rely heavily on fungicides including quinone outside inhibitor (QOI) fungicides. We collected 866 C. beticola isolates from sugar beet growing regions in France and Italy and assessed their sensitivity to the QOI fungicide pyraclostrobin. To gain an understanding of the molecular basis of QOI resistance, we cloned the full-length coding region of Cbcytb. All tested QOI-resistant isolates harbored a point mutation in Cbcytb at nucleotide position 428 that conferred an exchange from glycine to alanine at amino acid position 143 (G143A). A PCR assay was developed to discriminate QOI-sensitive and QOI-resistant isolates based on the G143A mutation. Our results indicate that QOI resistance has developed in some European C. beticola populations in Italy and monitoring the G143A mutation is an essential fungicide resistance management strategy.

Thesis (MScAgric)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: Leaf blackening, a postharvest disorder which is characterized by a dark brown to black discoloration, is found in most commercially important Protea cut flower species and cultivars. As this disorder is known to increase with storage time, it is a major concern to the South African industry as the use of sea freight is increasingly preferred due to lower transport costs and a more favourable carbon footprint. The cause of leaf blackening has been strongly linked to a carbohydrate stress exerted by the large inflorescence, thus requiring the utilization of sugar bound polyphenols in the foliage, which when removed, can oxidize enzymatically or non-enzymatically. A study where harvesting was done throughout the season as well as on selected days at 08:00, 12:00, 15:00 and 17:00, concluded that leaf blackening incidences in Protea cv. Sylvia stems varies significantly throughout the season, between years and even with the harvest time of day. Leaf blackening incidences increased from October onwards and remained high until February, before decreasing to acceptably lower levels towards March to May. Carbohydrate- and phenolic content together with water status of leaves at harvest was not able to accurately predict incidence of the associated leaf blackening. However, irrespective of the season of harvesting, leaf blackening was significantly lower when stems were harvested later in the day than compared to stems harvested in the morning. Low sucrose and high water content at these harvest times was positively correlated to high incidences of leaf blackening. In a next study where uptake dynamics of glucose pulsing was investigated, Protea cv. Sylvia was harvested at different times throughout the day, dehydrated to various levels and pulsed with an increasing range of glucose concentrations. Pulsing solution uptake per stem was found to be highly influenced by these factors, as dehydration of stems and a harvest time later during the day both decreased stem water potential, which then increased pulse-solution uptake within a certain time period. The daily harvest time influenced transpiration, whilst pulse-solution uptake decreased with an increase in glucose pulse concentration. When stems were pulsed pre-storage with an increasing range of glucose concentrations, not only did pulses of between 4.7 – 13.7% glucose significantly delayed the incidence of leaf blackening, but it also maintained a positive water balance longer in stems during vase life. Ethanol or acetaldehyde vapour did not provide a viable alternative for reducing leaf blackening incidence in Protea cv. Sylvia, although a synergistic effect was found when ethanol vapour or pulsing was used in combination with glucose. A commercial verification trial disclosed that Protea magnifica and Protea ‘Pink Ice’ reacted more beneficial to ethanol vapour than was observed in ‘Sylvia’. This study confirms that carbohydrate availability within the Protea cut stem remains a key factor in the control of leaf blackening. Factors which assist in maintaining high internal carbohydrate levels, such as enhanced glucose pulse uptake or effective vase solution utilization will contribute to providing an optimum control of leaf blackening during vase life following long-term cold storage.
AFRIKAANSE OPSOMMING: Loofblaarverbruining is ‘n na-oes defek wat gekarakteriseer word deur ‘n donker bruin na swart verkleuring wat voorkom in meeste kommersieël belangrike Protea snyblom spesies en kultivars. Hierdie defek is bekend daarvoor dat dit toeneem met stoortyd, dus is dit ‘n groot kommer vir die Suid-Afrikaanse industrie, met toenemende gebruik van seevrag as vervoer keuse wat laer vervoer kostes en meer gunstige ‘koolstof voetspoor’ bevoordeel. Die oorsaak van loofblaarverbruining word sterk gekoppel aan ‘n koolhidraat stres wat uitgeoefen word deur die groot bloeiwyse op die loofblare, waar suiker-gebonde polifenoliese verbindings ensiematies of nieensiematies geoksideer word met die verwydering van die suiker verbinding. 'n Studie waar geoes was regdeur die seisoen, sowel as op geselekteerde dae om 08:00, 12:00, 15:00 en 17:00, het bevind dat die voorkoms van loofblaarverbruining in stele van Protea kv. Sylvia aansienlik geskil regdeur die seisoen, tussen jare en selfs met die oes tyd gedurende die dag. Die voorkoms van loofblaarverbruining het toegeneem vanaf Oktober en het hoog gebly tot en met Februarie, voordat dit gedaal het tot aanvaarbare laer vlakke teen Maart, tot en met Mei. Koolhidraat-en fenoliese inhoud sowel as die water status van die blare by oes was onsuksesvol om die voorkoms van die gepaardgaande loofblaarverbruining akkuraat te voorspel. Loofblaarverbruining was egter aansienlik laer as stele geoes later in die dag teenoor stele geoes in die oggend, ongeag die seisoen van oes. Lae sukrose en 'n hoë water inhoud geassosieer met hierdie oes-tye was positief gekorreleerd met ‘n hoë voorkoms van loofblaarverbruining. In 'n volgende studie waar die opname dinamika van glukose pulsing ondersoek was, is Protea kv. Sylvia stele geoes op verskillende tye dwarsdeur die dag, gedehidreer tot verskillende vlakke en met 'n toenemende reeks van glukose konsentrasies gepuls. Pulsoplossing opname per steel is sterk beïnvloed deur hierdie faktore, aangesien dehidrasie van die stele asook stele geoes later gedurende die dag die afname van steel waterpotensiaal veroorsaak het, terwyl die puls-oplossing opname versnel het binne ‘n bepaalde tyd. Die tyd van oes beïnvloed ook transpirasie, terwyl vaas oplossing opname afgeneem met 'n toename in glukose puls konsentrasie. Wanneer ‘Sylvia’ stele gepuls was voor stoor met 'n reeks van toenemende glukose konsentrasies, het nie net die puls van tussen 4.7 – 13.7% glukose aansienlik die voorkoms van loofblaarverbruining vertraag nie, maar dit het ook ‘n positiewe water balans langer in stele gedurende die vaas lewe behou. Nie etanol of asetaldehied dampe is bevind as geskikte alternatief vir glukose pulsing om die voorkoms van loofblaarverbruining in Protea kv. Sylvia te verlaag nie, alhoewel ‘n sinergistiese effek waargeneem was wanneer etanol in kombinasie met glukose gebruik was. ‘n Kommersieële bevestigingstoetsing het bevind dat Protea magnifica en ‘Pink Ice’ meer voordeel uit ‘n ethanoldamp behandeling kon trek teenoor ‘Sylvia’. Hierdie studie het bevestig die belangrikheid van koolhidraat beskikbaarheid in die Protea snyblom, vir beheer van loofblaarverbruining. Faktore wat die handhawing van hoë interne koolhidrate vlakke, soos bevorderde glukose puls opname of effektiewe vaas oplossing benutting sal bydra tot ‘n optimal beheer van loofblaarverbruining tydens vaas lewe na langtermyn koueopberging.
National Research Fund (NRF) for their financial support in 2009; Protea Producers of South Africa (PPSA) and Productschap Tuinbouw (PT) as well as the Frank Batchelor Will Trust Grant for the financial support.

Dissertation (PhD (Agric))--University of Stellenbosch, 2000.
ENGLISH ABSTRACT: A study was made of the basic biology of subterranean Eriosoma lanigerum (Hausmann) populations in apple orchards in the Western Cape Province of South Africa. The absence of cornicles and the presence of a vulva could be used to identify 1st instar nymphs and adults respectively. Body length, body width and length of the hind femur are useful for separating 2nd , 3rd and 4th instars. However, separation of 2nd from 3rd instar nymphs was very unreliable. Maximum population growth rate was at 23°C while at 30 °C population growth was zero. The estimated minimum and maximum threshold temperatures for development were 4.32 and more than 30°C respectively. Numbers of underground E. lanigerum in soil samples taken using mechanical and hand augers were similar. However, numbers of aphids in samples were influenced by the distance from the trunk at which the samples were taken and the presence and the type of root material in the samples. More aphids were recorded close to the trunk, and at a given distance from the trunk more aphids were recorded if there was root material in the sample, especially if the roots were galled. early autumn (February, March) and declined during winter, especially if the winter rainfall was high. These cycles coincided with the nitrogen cycles in the roots. Embryos were also present in all instars throughout the year. There were more embryos in the 4th instar and adult aphids than in the other instars. The highest number of embryos in the 4th instar and adult aphids occurred during spring, which coincided with peak nitrogen levels in the roots of apple trees. Nitrogen levels in root material adjacent to galls and in ungalled roots were higher than in root galls. A number of entomopathogenic fungi, including species of Conidiobolus, Hirsufella and Beauveria were found. Their present contribution to biological control is not known. A straw mulch suppressed subterranean E. lanigerum population levels at least as well as the soil insecticide, imidacloprid, currently in use.
AFRIKAANSE OPSOMMING: 'n Studie van die basiese biologie van ondergrondse bevolkings van , Eriosoma lanigerum (Hausmann) is in appelboorde in die Weskaap Provinsie van Suid-Afrika uitgevoer. Die afwesigheid van kornikels en die aanwesigheid van 'n vulva kon gebruik word om die 1ste instar nimfe en volwassennes onderskeidelik te identifiseer. Liggaamslengte, liggaamsbreedte en die lengte van die agterste femur kon gebruik word om die 2de , 3de en 4de instars van mekaar te onderskei. Onderskeiding tussen 2de en 3de instar nimfe was egter baie onbetroubaar. Maksimum bevolkingsgroei het by 23°C plaasgevind, terwyl dit nul was by 30 °C. Die beraamde minimum en maksimum temperature vir ontwikkeling was by 4.32 en meer as 30°C onderskeidelik. Getalle van ondergrondse E. lanigerum in grondmonsters wat geneem is met gebruik van meganiese en hand bore was eenders. Getalle plantluise in monsters is egter beïnvloed deur die afstand vanaf die stam waarby die monsters geneem is en die teenwoordigheid van wortelmateriaal in die monsters. Meer plantluise is aangeteken as daar wortelmateriaal in die monsters was, en veral as daar galle op die wortels was. Die appelbloedluis was dwarsdeur die jaar ondergronds aktief. Bevolkingsvlakke het gedurende die vroeë somer (November, Desember) en vroeë herfs (Februarie, Maart) toegeneem, en gedurende die winter afgeneem, veral as die winterreënval hoogwas. Embrio's was ook teenwoordig dwarsdeur die jaar. Daar was meer embrio's in die 4de instar en volwasse plantluise as in die ander instars. Die hoogste aantal embrio's in die 4de instar en volwasse plantluise het in die lente voorgekom, wat saamgeval het met piek stikstofvlakke in die wortels van appelbome. Stikstofvlakke in wortelmateriaal aangrensend aan wortels en in wortels sonder galle was hoër as in wortelgalle. Talle entomopatogeniese swamme, insluitend spesies van Conidiobolus, Hirsufella en Beauvaria IS gevind. Hulle huidige bydrae tot biologiese beheer is nie bekend nie. 'n Strooideklaag het ondergrondse bevolkingsvlakke van E. lanigerum tot ten minste dieselfde mate as die grondinsektedoder, imidacloprid, wat tans in gebruik is, onderdruk.

Data for this study were collected by the US Forest Service and the Pennsylvania Bureau of Forestry on nearly 600 plots in central Pennsylvania. Tree and stand characteristics recorded between 1978 and 1985 include estimates of percent defoliation on individual trees. Logistic regression using maximum likelihood estimation was employed to model individual-tree mortality of 15 species in central Pennsylvania that had been defoliated by the gypsy moth. Defoliation was estimated to the nearest ten percent for individual trees. Other variables used for prediction included stand basal area and an individual-tree relative basal area index. Success ranged from no fit for three of the species to an R value (a derivation of Akaike's information criterion) of .613 for white oak. The inclusion of defoliation in the models had a varied effect. For four of the species percent defoliation was not significant. For hickory and white oak respectively, percent defoliation raised the R value by .305 and .290 percentage points. As many as five models for each species were developed: one or two models with no defoliation measure in the model and one each for one, two or three consecutive years of defoliation measures. A beta and gamma function were used to model individual· tree basal area growth for the same 15 species. The models were fit using nonlinear least squares. Variables used include the relative basal area index, stand basal area, site index and a defoliation index that incorporated three years of individual-tree, percent defoliation. The beta and gamma functions fit equally well with values of (1 - relative mean square error) ranging from .1967 to .6290. Results for both models are presented for each species. The defoliation index was a significant variable for five of the fifteen species: white, chestnut, red, and black oak and sassafras.
Master of Science

The effects of gypsy moth defoliation on acorn production (the seed source for oak regeneration), and the forest floor regeneration environment were investigated. Parameters measured included: acorn quantity, weight, development, and viability; litterfall; and forest floor depth and biomass. Nineteen plots in north-central Virginia and western Maryland on which trees suffered heavy, moderate, or no defoliation were monitored over a two-year period.

Master of Science

Deoxynivalenol (DON), a mycotoxin produced in cereal grains infected by Fusarium Head Blight produced by Fusarium graminearium and Deoxynivalenol-3-?-D-glucopyranoside (DON-3G), were studied during processing using LC-MS-MS and GC. DON reduced significantly (P<0.05) 61.8% during milling into flour. Therefore, DON was concentrated mostly in the bran and germ. DON increased 40.8% during the fermentation stage of baking. DON increased in dough more than flour and mixed dough. Milling reduced by 23.7% but fermentation did not. But bread was significantly lower in DON-3G at 0.15 ppm than flour and dough at 0.31 ppm. The baking increased DON and decreased DON-3G showing a difference in stability of the mycotoxins during processing. Enzyme hydrolysis on DON using ?-amylase, cellulase, protease, and xylanase, showed a significant increase with cellulase (20.8%), protease (11.4%), and xylanase (35.6%) compared to wheat composite. DON may be bound to the cell wall or protein component of the kernel.

Bibliography: leaves 81-100. Entry of inoculum into a crop and disease development in the crop cannot be prevented because spores are airborne and there is a lack of highly resistant varieties. This makes complete control of chocolate spot unlikely. It should however, be possible to improve current levels of disease control through the integration of the factors identified in the study.

Polyclonal antisera produced against spores, soluble protein and the whole mycelium fractions of Didymella lycopersici reacted with the homologous and heterologous antigens. The most sensitive antiserum was that raised against the whole mycelium, the soluble protein and the spore, in decreasing order of sensitivity. Using the antiserum raised against the whole mycelium it was possible to detect D. lycopersici on diseased plants and infested seeds. Cross reactivity was observed between the antisera produced to D. lycopersici and D. applanata, D. bryoniae and other tomato fungal pathogens including Fusarium spp. and B. cinerea. ELISA was most sensitive and reliable compared to double immunodiffusion, and latex tests. No reactions were obtained using the latex agglutination procedure and no antiserum detected spores in double diffusion tests. Protein profiles on SDS-PAGE revealed that the total number of protein bands decreased with increased age of cultures of D. lycopersici incubated in liquid media. Western blots probed with the antiserum raised against the whole mycelium showed that protein bands from extracts of both D. lycopersici and D. applanata were antigenic.
Land and Food Systems, Faculty of
Graduate

Blueberry bushes with scorch symptoms were found during a survey of blueberry fields in British Columbia, Washington, and Oregon. Some of these bushes were infected with blueberry scorch virus (BBScV) while others contained a second virus which was sap transmissible to Nicotiana clevelandii, N. benthamiana, and N. tabacum cv. 'Havana 425' . This virus was purified from N. clevelandii and had isometric particles of approximately 30 nm in diameter, a coat protein subunit of 27,500 daltons and a tripartite genome. I was unable to transfer the virus from either infected N. clevelandii or infected blueberry to healthy N. clevelandii with Myzus persicae or Fimbriaphis fimbriata. Serological tests of this blueberry virus with antisera against members of the ilar-, cucumo-, bromo-, or nepovirus groups failed to indicate any relationship. In a subsequent survey using enzyme-linked immunosorbent assay, this isometric virus was found in blueberry plants from northern Washington state to central Oregon but has not yet been found in B.C. Of the established members of the carlavirus group examined, BBScV is most closely related to potato virus S (PVS) and less closely related to carnation latent virus (CLV) and potato virus M (PVM). The difference in host range between BBScV and PVS would indicate that the BBScV is not a strain of PVS but is a separate virus that is related to PVS. Therefore, BBScV should be renamed blueberry scorch carlavirus (BBSCV). BBSCV was also compared to a carlavirus isolated from blueberry in the Sheep Pen Hill blueberry growing area of New Jersey (referred to as SPHV). These viruses were compared serologically and by use of nucleic acid hybridizations. BBSCV and SPHV were found to be closely related and were concluded to be strains of the same virus. SPHV should be named the New Jersey strain of BBSCV.
Land and Food Systems, Faculty of
Graduate

Ramets of 14 clones of western black cottonwood Populus trichocarpa Torr. & Gray collected from the interior and coast of British Columbia were tested in the nursery for their growth performance after infection by the leaf rust Melampsora occidentalis Jacks. Linear relationships were demonstrated between various growth parameters (total dry weight, stem dry weight, root dry weight, volume, diameter and height) and disease severity rated as diseased leaf-weeks divided by total leaf-weeks. Losses due to rust infection included reduced total dry weight and volume growth in the year of heavy disease, the death of severely infected ramets during the following winter and reduced initial volume increment in the following growing season. The percentage reduction in yield (total dry weight) was greater than the cumulative percent leaf area infected, suggesting that the rust infected leaf parts act as sinks for photosynthate. The normal pattern of photosynthate allocation was altered in favour of the top growth of ramets. Ratios of stem/root dry weight increased rapidly as disease level increased. A threshold infection level, below which no loss occurred, was not detected in this pathosystem. Significant variation in rust resistance of black cottonwood clones was detected both within and between the two geographic areas. Clones from the coast or warm, moist areas were, on average, more resistant than clones from the interior or cold, dry climates. The phenomenon of induced resistance was not detected at either the local or the systemic levels in black cottonwood challenged by the rust. Variation in rust tolerance among black cottonwood clones was demonstrated. Rust tolerance was defined as the slope of the relationship between yield of ramets (expressed as a proportion of controls) and disease severity (expressed as the proportion of the total number of leaf-weeks infected). A negative correlation between rust tolerance and rust resistance was found. In the collection of clones tested, the positive effect of disease resistance on the growth of cottonwood clones was partially counterbalanced by the negative effect of reduced tolerance on the growth. The importance of this relationship in both natural and artificial selection of superior trees against disease is indicated.
Forestry, Faculty of
Graduate

Forest insects and diseases active in immature interior spruce stands in the central interior of British Columbia and their possible implications in forest management practices have been surveyed. Collection records, spanning the period 1949 to 1982, from the Forest Insect and Disease Survey of the Canadian Forestry Service were reviewed for the Prince George Timber Supply Area and the pest incidence in immature interior spruce stands summarized. Twenty-two plantations, established between 1963 and 1973, were surveyed to determine the relative incidence of the major insect and pathogen pests of immature spruce in Supply Block 'G' of the Prince George Timber Supply Area. A bud midge, likely Rhabdophaga swainei Felt (Diptera: Cecidomyiidae), and a terminal weevil, Pissodes strobi Peck (Coleoptera: Curculionidae), were found to consistently infest and damage a significant number of immature interior spruce trees. A spruce stand stocking profile was developed as a basis for discussion of management practices in plantations and immature stands. The stocking profile can be used in the determination of not only pest management policy decisions but in stand management decisions affecting stand density and, ultimately, merchantable yield at harvest. The findings confirmed that forest management must be actively practiced throughout the life of a forest stand. To be successful, however, stand management guidelines and merchantable yield projections are required. These guidelines and projections must include the influences of insects and diseases upon the forest crop in their development model. This information is particularly important in the development of complete Timber Supply Area plans and for the flagging of pest hazard periods during the development of spruce forests.
Forestry, Faculty of
Graduate

The effect of interrupted leaf wetness (IWP) and %RH on infection by Cercospora carotae (Pass.) Solh. was studied by inoculating carrot leaves (Daucus carota var sativa DC. L.) and subjecting the plants to different IWP treatment, continuous leaf wetness (CWP) and to different combinations of %RH and temperature with and without an initial wet period of 6 hr. IWP significantly reduced infection as compared to CWP. Infection was optimal under leaf wetness and decreased with decrease in percent RH. The effect of temperature and duration of moist period on sporulation of C. carotae was studied on carrot plants under leaf wetness, 96%RH, and 96%RH with an initial 12 hr of leaf wetness. For all types of moisture conditions, sporulation increased with the increase in temperature up to the optimum (28$ sp circ$C) and then declined. Logistic and polynomial models were used to describe the effect of temperature and time on sporulation under these moisture conditions. The incubation period of Cercospora carotae was studied in the field. First lesions were observed 6 to 8 days after inoculation and new lesions appeared until the 10th to 14th day. The beginning, mean, and end of incubation period was modelled as a function of mean daily temperature and mean daily RH $ ge$ 90%. A model describing lesion appearance as a function of time was developed using a logistic function (R$ sp2$ = 0.84). A prediction model containing series of equations that described mathematically the interaction among predicted inoculum, infection and sporulation equivalents for the environment was developed and validated. In general, the model predicted adequately Cercospora blight progress. A weather-based forecasting system was developed to time the first fungicide spray to manage Cercospora blight of carrot based on the accumulation of critical number of disease severity units.