Thesis (MScAgric (Plant Pathology))--University of Stellenbosch, 2005. / The genus Rhizoctonia includes important soilborne plant pathogens that can cause severe economic losses on a wide range of crops including cereal, canola, pasture and grain legume crops. Limited information is available on specific anastomosis groups (AGs), nuclear status, pathogenicity and cross-pathogenicity of Rhizoctonia isolates associated with each of these crops in the Western Cape province. Therefore, these aspects were investigated in this study, since information in this regard is crucial for the development of Rhizoctonia disease management practices.

Thesis (MSc)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Five new species of ophiostomatoid fungi, colon ising the infructescences of serotinous Protea species, have recently been discovered in South Africa. Prior to this, ophostomatoid fungi were thought to be restricted to the Northern Hemisphere. The discovery of these five species thus extensively expanded the known geographical range of these fungi, now also to include the Southern Hemisphere. Since this discovery, few studies have focused on the interesting ecology of this group, which is uniquely adapted for spore dispersal by arthropods. Studies focussed on ophiostomatoid fungi provide an unique opportunity to study inter-organism interactions between fungi, their host plants and the arthropods responsible for their spore dispersal. Very few similar studies have been undertaken, particularly in the Fynbos Biome, to which most of our economically important Protea species are confined. The current study provides insight into some ecological aspects of these complex interactions. The seasonal distribution of the ophiostomatoid fungi associated with the infructescences of members of the Proteaceae was investigated. Definite seasonal patterns were observed, with peak fungal colonisation occurring during the wetter winter months. While determining the host specificity of these fungi, a new Protea host for Ophiostoma splendens was identified, and a new species of Rhyncomeliola was discovered. All ophiostomatoid species native to Fynbos in the Stellenbosch region are exclusively associated with the infructescences of species in the plant genus Protea. By employing a multiplex Polymerase Chain Reaction (PCR), a set of group specific primers was developed for the identification of South African Ophiostoma and Gondwanamyces fungal DNA. This newly developed method was used to scan arthropods collected from the infructescences of P. repens for the presence of 0. splendens and G. proteae spores. By using these group-specific primers, three insects possibly responsible for long range dispersal of fungal spores were identified. Three further insect species, possibly contributing to the short-range dispersal of ophiostomatoid spores, were also implicated through this method. All arthropods associated with the fruiting structures of selected members of the Proteaceae were also investigated. A total of 62 pseudospecies (ca. 7500 individuals), belonging to 45 different arthropod families, were collected. Proteaceae species with larger fruiting structures housed more arthropod species and higher numbers of individuals than Proteaceae taxa with smaller fruiting structures. Some plant species housed similar arthropod communities, while others housed unique suites of arthropods. Seasonal patterns in arthropod numbers were observed, and it was found that, in most instances, arthropod numbers peaked during the autumn and winter months. Twenty-five fungal taxa were isolated from various Proteaceae arthropods, many of which are genera known to include Proteaceae pathogenic species. Ophiostomatoid fungi have a saprophytic relationship with their Protea hosts, and may deter some of these potentially harmful fungi from colon ising the infrutescences. Some fungi showed a high degree of specificity towards potential vectors, while others were found on a diverse range of arthropods. This study highlights the existence of complex inter-organismal interactions within the Fynbos Biome, a study area where the interactions between plants, fungi and insects have been grossly neglected. The few studies that have been conducted in this field have mostly focussed on a limited number of organisms, and no wide-scale attempts, such as presented here, have been published. It is important to obtain a holistic view in any ecological study that focuses on interactions between different suites of organisms. Ultimately this will aid in the development of better conservation strategies. This study thus provides a muchneeded start in studies on multi-organismal interactions in the Fynbos Biome. / AFRIKAANSE OPSOMMING: Vyf nuwe ophiostoma-agtige fungus spesies is onlangs in die vrug-liggame van Suid Afrikaanse Protea plante ontdek. Voor hierdie ontdekking, was die algemene opvatting dat ophiostoma-agtige fungi beperk is tot die Noordelike Halfrond. Die ontdekking van hierdie vyf spesies het dus die bekende geografiese verspreiding van hierdie tipe fungi vergroot om nou ook die Suidelike Halfrond in te sluit. Sederdien het min studies gefokus op die interesante ekologie van hierdie groep, wat aangepas is vir spoorverspreiding deur geleedpotiges. Studies wat fokus op die ophiostoma-agtige fungi voorsien 'n unieke geleentheid om die inter-organismiese-interaksies tussen fungi, hul gasheer plante en die geleedpotiges wat hul spore versprei, te bestudeer. Baie min soortgelyke studies is al voorheen in die Fynbos Bioom, waar die meeste van ons ekonomies-belangrike Protea spesies voorkom, onderneem. Die huidige studie verleen meer inligting oor sommige ekologiese aspekte van hierdie komplekse interaksies. Seisoenale verspreidingspatrone van ophiostoma-agtige fungi geassosieer met die vrug-liggame van lede van die Proteaceae, is ondersoek. Daar is defnitiewe seisoenale patrone in die aanwesigheid van fungi gevind, met 'n piek in fungi kolonisasie-getalle gedurende die vogtiger wintermaande. 'n Nuwe Protea gasheer vir Ophiostoma splendens en 'n nuwe fungus spesie (Rhyncomeliola sp.), is ontdek. Alle Fynbos ophiostoma-agtige spesies in die Stellenbosch area, is beperk tot Protea spesies. 'n Multipleks Polimerase Ketting Reaksie is ontwikkel om die spesifieke DNS van ophiostoma-agtige fungi te herken. Hierdie metode is gebruik om te toets vir die aanwesigheid van spore van hierdie fungi op die liggame van geleedpotiges (geassosieerd met P. repens). Hierdeur is drie insekte wat waarskynlik verantwoordelik is vir die langafstand verspreiding van spore geidentifiseer. Drie verdere insekte wat moontlik verantwoordelik is vir die kortafstand verspreiding van ophiostoma-agtige fungi is ook aangewys. Alle geleedpotiges geassosieer met die vrugstrukture van geselekteerde lede van die Proteaceae is ondersoek. 'n Totaal van 62 pseudo-spesies (omtrent 7500 individue), wat tot 45 families behoort, is versamel. Proteaceae spesies met groter vrugstrukture het meer geleedpotige spesies en individue gehuisves as taksa met kleiner vrugstrukture. Sommige plant spesies het soortgelyke geleedpotige gemeenskappe gehuisves, terwyl unieke groepe geleedpotiges in ander plante voorgekom het. Alhoewel die geleedpotiges seisonale variasies in getalle geopenbaar het, het die meeste groepe 'n piek in getalle getoon gedurende die herfs- en wintermaande. Vyf-en-twintig fungi taksa is geïsoleer vanaf verskeie Proteaceae geleedpotiges. Sommige van hierdie is genera wat Proteaceae patogeniese spesies insluit. Sommige fungi het 'n hoë graad van spesifisiteit teenoor potensiële vektore getoon, terwyl ander weer algemeen op verskeie geleedpotige spesies gevind is. Hierdie studie dui op die bestaan van komplekse inter-organismiese-interaksies in die Fynbos Bioom, in 'n area waar die studie van interaksies tussen plante, fungi en insekte nog baie min aandag geniet het. Die beperkte aantal studies wat tot dusver in hierdie veld onderneem is, fokus gewoonlik slegs op 'n paar organismes. Geen grootskaalse studies, soos die een hier voorgelê, is al gepubliseer nie. In enige ekologiese studie wat fokus op interaksies tussen verskeie organismes, is dit belangrik om 'n holistiese siening te probeer verkry. Uiteindelik sal dit bydra tot die ontwikkeling van beter bewarings-strategië. Hierdie studie verleen dus 'n noodsaaklike begin tot studies op multiorganismiese- interaksies.

A Araucaria angustifolia é uma espécie vegetal de vital importância para a manutenção da Floresta Ombrófila Mista (Floresta de Araucária), ecossistema no qual ocorre naturalmente. A araucária apresenta elevado valor sócio-econômico e ambiental e, devido à intensa exploração predatória a que foi submetida, hoje se encontra criticamente ameaçada de extinção. A destruição dessa preciosa espécie vegetal ocasionaria graves consequências ao ecossistema, que poderiam envolver a redução da diversidade de inúmeros animais, plantas e micro-organismos, os quais estão intimamente associados e apresentam grande dependência de A. angustifolia. Pesquisas envolvendo particularmente a caracterização de rizobactérias promotoras do crescimento de plantas (RPCP), nunca foram realizadas em A. angustifolia. Assim, o objetivo do presente estudo foi realizar o isolamento, a seleção e a caracterização de rizobactérias com potencial de promoção do crescimento e biocontrole de fungos fitopatogênicos em A. angustifolia. Os isolados obtidos foram selecionados quanto à capacidade para a promoção do crescimento por meio da produção de ácido indolacético (AIA), solubilização de fosfato inorgânico, produção de fosfatases, fixação assimbiótica de N2, este último através da análise de acúmulo total de nitrogênio em meio de cultura e análise de redução do acetileno (ARA). Também foram selecionadas rizobactérias através da avaliação de mecanismos indiretos de ação, como produção de sideróforos e antagonismo a Fusarium oxysporum, Cylindrocladium candelabrum e C. pteridis, fitopatógenos de espécies arbóreas. Os isolados mais promissores foram caracterizados através da análise do perfil de ácidos graxos da membrana celular (FAME), BOX-PCR e sequenciamento parcial do gene 16S rRNA. Foram isoladas 97 rizobactérias, sendo submetidas aos testes fenotípicos. Todos os isolados apresentaram ao menos uma característica positiva para os mecanismos de promoção do crescimento avaliados, excetuando-se a produção de quitinases. Dentre os isolados obtidos, 18 produziram AIA, 27 foram capazes de solubilizar fosfato inorgânico, 37 foram positivos para sideróforos e 83 foram hábeis produtores de fosfatases. Com relação à fixação assimbiótica de N2, 20 isolados foram positivos para a formação de película em meio de cultura livre de nitrogênio, no entanto, nenhum diferiu significativamente do controle, sem nitrogênio, quando analisado o acúmulo deste elemento em meio de cultura. Por outro lado, 3 isolados foram capazes de reduzir acetileno a etileno. Quarenta e cinco isolados formadores de endósporos apresentaram antagonismo a F. oxysporum. Os isolados B4, B15, B27, B35, B36, B42 e RISP2, caracterizados como Bacillus spp., destacaram-se como bons antagonistas aos fitopatógenos avaliados. Também foi verificada a presença de estirpes com múltiplos mecanismos de ação. A análise genotípica dos isolados mais promissores através da técnica de BOX-PCR apresentou a formação de dois grandes grupos, expressando nitidamente o agrupamento dos isolados formadores de endósporo. A técnica FAME e o sequenciamento do gene 16s rRNA concordaram em caracterizar os melhores isolados como pertencentes às famílias Bacillaceae (9 isolados), Enterobacteriaceae (11) e Pseudomonadaceae (1). Até onde sabemos, este é o primeiro estudo a relacionar a espécie Ewingella americana a diversos mecanismos de promoção do crescimento. Osresultados obtidos demonstram grande potencial de aplicabilidade dessas rizobactérias como biofertilizantes e no controle biológico de fitopatógenos em A. angustifolia. / Araucaria angustifolia is a plant species of vital importance for the maintenance of the Mixed Ombrophylous Forest (Araucaria Forest) ecosystem in which it occurs naturally. Araucaria has a high socio-economic and environmental value, and due to its intense predatory exploitation, it is critically endangered. The destruction of this precious plant species would cause serious consequences to the ecosystem, which could involve a reduction of the diversity of many animals, plants and microorganisms, which are closely associated and reveal a great dependence on A. angustifolia. Studies involving plant growth promoting rhizobacteria (PGPR) and their characterization have never before been performed in A. angustifolia. The objective of this study was to isolate, select and characterize rhizobacteria with potential for growth promotion and biocontrol of plant pathogenic fungi in A. angustifolia. The isolates were selected by means of their potential to produce indole acetic acid (IAA), to solubilize inorganic phosphate, to produce phosphatase, and for asymbiotic N2 fixation. The latter was estimated by analyzing the accumulation of nitrogen in the culture medium and by the acetylene reduction assay (ARA). Rhizobacteria were also selected through the evaluation of indirect action mechanisms such as siderophore production and antagonism to Fusarium oxysporum, Cylindrocladium candelabrum and C. pteridis, all pathogens of trees. The most promising isolates were characterized by analyzing the fatty acid methyl ester (FAME), by BOX-PCR and partial sequencing of the 16S rRNA gene. Ninety seven rhizobacteria were isolated and subjected to the phenotypic tests. All isolates presented at least one positive feature, characterizing them as potential PGPR, except for the production of chitinases. Among these isolates, 18 produced IAA, 27 were able to solubilize inorganic phosphate, 37 were positive for siderophores and 83 were phosphatases producers. Regarding the asymbiotic N2 fixation, 20 isolates were effective in the pellicle formation in nitrogen free culture medium, however, none differed significantly from the control, when analyzed for the accumulation of N in the culture medium. Furthermore, three isolates were able to reduce acetylene to ethylene. Forty five isolates were endospore formers and antagonistic to F. oxysporum. The isolates B4, B15, B27, B35, B36, B42 and RISP2, characterized as Bacillus spp. stood out as good antagonists of the evaluated plant pathogens. We also observed the presence of strains with multiple mechanisms of action. Genotypic analysis of the most promising isolates by the BOX-PCR technique showed the formation of two major groups, expressing clearly the grouping of isolates forming endospores. Both techniques, FAME and PCR, resulted in the same grouping of the most effective isolates as belonging to Bacillaceae (9 isolates), Enterobacteriaceae (11) and Pseudomonadaceae (1). As far as we know, this is the first study to include the bacterium Ewingella americana among the PGPR. The results demonstrate a potential application of these rhizobacteria as biofertilizers and for biological control of plant pathogens in A. angustifolia.

Atualmente, a videira Niagara Rosada é a variedade de uva de mesa mais cultivada no Estado de São Paulo, Brasil. Contudo, sua produtividade e custo de produção têm sido afetados pela ocorrência de doenças fúngicas, principalmente o míldio, causado pelo fungo Plasmopara viticola. Para o controle dessa doença, têm sido feitas pulverizações com fungicidas, as quais muitas vezes em excesso. Dentre as variáveis meteorológicas que influenciam a ocorrência de doenças fúngicas nas plantas, a duração do período de molhamento (DPM) é uma das mais importantes. A presença de molhamento sobre a superfície das plantas provê a água requerida pelos patógenos para o processo de germinação e infecção do tecido foliar. Visando a subsidiar sistemas agrometeorológicos de alerta fitossanitário, cuja finalidade é possibilitar a racionalização do uso de fungicidas, os objetivos do presente estudo foram: determinar a posição da videira com a DPM mais longa e sua relação com a DPM medida na posição padrão, a 30 cm de altura sobre o gramado; avaliar a estimativa da DPM sobre o gramado por diferentes modelos a partir de dados meteorológicos obtidos em uma estação meteorológica padrão e verificar as relações entre a DPM estimada para o gramado e a DPM medida no vinhedo; e correlacionar a epidemiologia do míldio (P. viticola) durante o ciclo da videira Niagara Rosada, sem controle químico, com as variáveis DPM medida no vinhedo (posição da videira com a DPM mais longa), DPM estimada na posição padrão sobre o gramado pelo melhor modelo, assim como com outras variáveis meteorológicas. A DPM foi medida em posição padrão sobre o gramado e em quatro diferentes posições da videira: topo da planta com a face superior do sensor voltada para sudoeste e nordeste (Topo-SW e Topo-NE) e altura dos cachos de uva com a face superior do sensor voltada para sudoeste e nordeste (Dossel-SW e Dossel-NE). A epidemiologia do míldio foi avaliada sem controle químico, utilizando-se escala de notas de 0 a 4, com nove níveis de severidade, para as folhas e cachos da videira. No estudo da variabilidade espacial da DPM, não houve diferença significativa entre a parte mais alta (1,6 m) e a parte mais baixa (1,0 m) da videira, assim como entre as faces sudoeste e nordeste das plantas. Ao se analisar a relação entre a DPM sobre o gramado e a DPM nas diferentes posições da videira obtida por meio de regressão linear simples, observou-se uma boa correlação, com R2 = 0,88. Na avaliação dos modelos de estimativa da DPM, o modelo CART foi o que teve o melhor desempenho sobre o gramado, sendo que esta estimativa também apresentou uma boa correlação com a DPM medida no interior do vinhedo. Isso permitiu concluir que é possível estimar a DPM no vinhedo de Niagara Rosada a partir de medidas ou estimativas da DPM na estação meteorológica padrão. Na modelagem do desenvolvimento do míldio, a DPM esteve presente nas melhores correlações com a severidade do míldio na videira Niagara Rosada, mostrando a grande importância desta variável para a ocorrência de doenças fúngicas nos vinhedos. / Nowadays, the \'Niagara Rosada\' grapevine is the most cultivated table grape variety in the State of São Paulo, Brazil. However, yield and production cost of this grapevine have been affected by fungal diseases, mainly downy mildew, caused by Plasmopara viticola fungus. For controlling this disease, producers have been applied an excessive number of sprays with fungicides. Among the meteorological variables that influence the occurrence of fungal plant diseases, leaf wetness duration (LWD) is one of the most important. The wetness presence on plant surface provides the water required by the phatogens to germinate and to infect leaf tissues. Aiming to subsidize the plant disease warning systems, which has as purpose to rationalize the use of fungicides in the vineyards, the objectives of the present study were: to determine the canopy position of the Niagara Rosada table grape with longer LWD and its correlation with measured standard LWD over turfgrass; to estimate LWD over turfgrass considering different models with data from a standard weather station, and to evaluate the correlation between estimated LWD over turfgrass and LWD measured in the vineyard; and to correlate downy mildew occurrence in the vineyard, without chemical control, with measured LWD at the vineyard (canopy position with longer LWD), with estimated LWD in standard condition over turfgrass for the best model, and with other meteorological variables. LWD was measured in standard condition over turfgrass and in four different canopy positions of the vineyard: at the top of the plants, with sensors facing southwest and northeast (Top-SW and Top-NE), and at the grape bunches height, with sensors facing southwest and northeast (Bottom-SW and Bottom-NE). The downy mildew epidemiology during the grapevine cycle was evaluated without chemical control, using scores ranging from 0 to 4, with nine severity levels, for leaves and bunches of grapevine. When the spatial variability of LWD was studied, no significant difference was observed between the top (1.6 m) and the bottom (1.0 m) of the canopy and also between the southwest and northeast face of the plants. The analysis of the relationship between standard LWD over turfgrass and crop LWD in different positions of the grape canopy showed a define correlation (R2 = 0.88). Among the LWD estimative methods, CART was the one with the best performance to estimate LWD over turfgrass. The results from this model also presented a good correlation with measured LWD inside the vineyard, showing that LWD can be estimated for this crop with data from a nearby standard weather station. For the downy mildew modeling, LWD also present the best correlations with disease severity in the \'Niagara Rosada\' vineyard, showing the great importance of this variable for fungal diseases occurrence in this crop.

Graduation date: 1994

No description available.

No description available.

Six pathogenic fungal species were isolated from naturally-infected Echinochloa species and evaluated as biological control agents for E. crus-galli, E. colona, and E. glabrescens in rice. Bipolaris sacchari, Curvularia geniculata, and Exserohilum monoceras were non-pathogenic to rice and caused high mortality of Echinochloa species. E. monoceras was selected for further study. Under regulated greenhouse conditions, an inoculum dose of 2.5 $ times$ 10$ sp7$ conidia/m$ sp2$ killed E. crus-galli and E. glabrescens seedlings while 5.0 $ times$ 10$ sp7$ conidia/m$ sp2$ caused 100% mortality of E. colona seedlings. The 1.5-leaf stage was the most susceptible growth stage for all three Echinochloa species. E. glabrescens was most susceptible to E. monoceras infection, E. crus-galli had an intermediate susceptibility, and E. colona was least susceptible. The optimum temperature for 100% mortality was between 20 and 30 C for all Echinochloa species, whereas the minimum dew period for 100% mortality was 16 h for E. colona, 12 h for E. crus-galli, and 8 h for E. glabrescens. Under screenhouse conditions and in the absence of an artificial dew period, over 90% of Echinochloa seedlings were killed when inoculum was sprayed in an oil emulsion or when applied as a dry powder to the water surface of a simulated paddy field. Maximum conidia production occurred on V-8 juice agar or centrifuged V-8 juice agar, at 28 C in the dark. No conidia were produced in liquid media. Of various agricultural products tested as solid substrates, the highest sporulation (1.81 $ times$ 10$ sp6$ conidia/g dry weight) occurred on corn leaves. Host range tests on 54 plant species in 43 genera and 19 families showed that Rottboellia cochinchinensis, was also highly susceptible to this fungus. Of the crops tested, only corn seedlings were lightly infected under optimum greenhouse conditions but no disease occurred on corn under field conditions. Bipolaris sacchari, Exserohilum monoceras, and E. oryzae

No description available.

Lupines (Lupinus albus L.) can provide high levels of good quality protein for human and animal nutrition. Unlike soybeans, lupine seeds do not need to be processed before consumption. Being a member of the legume family, lupines improve soil structure and fertility. Lupines also have the advantage of being able to grow in cooler climates and in fields of lower fertility than soybean. Lupine production is relatively new in Eastern Canada and new diseases limit production in this region. In 1990, a Phoma sp. was isolated from diseased lupine in Quebec and Nova Scotia. This research was undertaken to acquire further knowledge about this lupine pathogen. The morphological characteristics of this fungus do not exactly fit the description of any other Phoma sp., but it is very close to P. pinodella. This Phoma sp. on lupines may be a new variety of P. pinodella affecting lupine in particular. In vitro, mycelium grew over a wide range of temperatures (5°--35°C), the optimal temperature being 25°C. Spore germination occurred under different conditions of temperature, from 10°C to 35°C, the optimum being 25°C. Spores germinated at relative humidities from 94% to 100%, (-7.027 to 0 MPa) the optimum being between 98% and 100% (-2.768 to 0 MPa). In controlled environment, disease symptoms appeared over a wide range of leaf wetness durations (8 h--36 h) and temperature regimes (15°C--30°C). The most extensive disease symptoms occurred following 36 hours of leaf wetness duration at 30°C. This Phoma sp. survived over winter in infected stubble of lupines of the previous year crop. The infected crop residue may be another source of inoculum of this seedborne pathogen.