Doctor of Philosophy / Department of Plant Pathology / Megan Kennelly / Large patch, caused by the fungus Rhizoctonia solani anastomosis group (AG) 2-2 LP, is the most common and severe disease of zoysiagrass (Zoysia spp). Despite the importance of this disease, few studies have examined pathogen biology, cultivar susceptibility, cultural controls, and chemical controls. The objectives of this dissertation were: (1) Characterize large patch isolates based on anastomosis pairing, in-vitro mycelial growth rates, nuclear counts, virulence, PCR, and amplified fragment length polymorphism (AFLP); (2) Determine the effects of cultivation (aerification, verticutting, and sand topdressing) on disease severity; (3) Evaluate different fall and spring applications of the fungicides flutolanil, azoxystrobin, and triticonazole; (4) Evaluate the susceptibility of fifteen new zoysiagrass germplasm lines from parental crosses including Z. japonica, Z. matrella, and Z. pacifica. All the R. solani isolates from large patch-infected zoysiagrass from Kansas belonged to AG 2-2 LP. Variations were observed among the isolates in their average number of nuclei per cell, mycelial growth rates and virulence. There was also variation in the amplified fragment length polymorphism (AFLP) DNA fingerprints, suggesting possible underlying genetic differences of biological significance among members of AG 2-2 LP. Cultivation did not affect soil moisture or temperature. Cultivation also did not reduce patch sizes, nor influence turf recovery rate from large patch. From 2009 to 2011, spring and fall N fertility was consistently associated with lower percentages of diseased turf in both cultivated and non-cultivated plots at Manhattan and Haysville. In general, two fall applications of fungicide did not reduce disease compared to one fall application. Fungicides applied in the fall when thatch temperatures ranged from 17.8oC to 23.2oC reduced disease compared to untreated controls. Early spring applications reduced disease compared to later spring applications. In germplasm screening studies, all progeny had similar disease levels compared to Meyer in the growth chamber, but only 6 consistently had disease levels as low as Meyer in the field. Growth chamber results did not correlate to field results.

Made available in DSpace on 2017-07-25T19:30:48Z (GMT). No. of bitstreams: 1 GISLAINE GABARDO.pdf: 1835122 bytes, checksum: 11f8d6244d587bd02e0025385165e5a5 (MD5) Previous issue date: 2015-02-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The use of plant defense mechanisms inducers may increase the disease control spectrum in soybean. The objective of this study was to abiotic and biotic resistance inducers in experiments in detached leaves and field conditions in soybean. The experiments with detached leaves were conducted in the laboratory, since the field experiment was conducted at the Fazenda Escola Capão da Onça in the harvest 2013/2014. The experimental design for the experiment of detached leaves was completely randomized in a factorial arrangement (7 x 2), with five replications. The field experiment was adopted the design of a randomized block design with four replications. Treatments for the experiments were: 1 - control; 2 - acibenzolar-S-methyl (Bion 500 WG; 3 - calcium (Max Fruit; 4 - micronutrients: copper, manganese and zinc (Wert Plus; 5 - micronutrients: manganese, zinc and molybdenum (V6; 6 - NK fertilizer (Hight Roots; 7 - Ascophyllum nodosum (Acadian and 8 - azoxystrobin + cyproconazole (Priori XTRA with addition of Nimbus adjuvant. Were evaluated by the detached leaf method inducers against Phakopsora pachyrhizi, Sclerotinia sclerotiorum and Rhizoctonia solani. No difference in treatments for P. pachyrhizi. For Rhizoctonia solani and S. sclerotiorum was no difference highlighting treatment with A. nodusum and micronutrients: copper, manganese and zinc and manganese, zinc and molybdenum, respectively. In the experiment, were made 4 applications of resistance inducers (phenological stages V3, V6, R1 and R5.1) and two of the fungicide (phenological stages R1 and R5.1). The characteristics evaluated were: severity of downy mildew (Peronospora manshurica), powdery mildew (Microsphaera diffusa), rust (P. pachyrhizi), final disease cycle (DFC), defoliation, yield components, yield and germination and health of harvested seeds. With the data of severity calculated the area under the disease progress curve (AUDPC). Substitutes controlled the mildew, but had no effect on powdery mildew, rust, DFC and defoliation. The fungicide treatment was the one who controlled the rust, powdery mildew, DFC and defoliation. Cultivate the yield components those affected by the treatments were the number of pods per plant and thousand kernel weight. Treatment with fungicide had the highest productivity. Defoliation was strongly correlated with the PMG, emphasizing the importance of maintaining the leaf area to ensure grain filling. Foliar treatments and the best treatments NK fertilizer and fungicide affected the germination and seed health. / O uso de indutores de mecanismos de defesas das plantas pode aumentar o espectro de controle das doenças na cultura da soja. O objetivo deste trabalho foi estudar indutores de resistência abióticos e biótico em experimentos em folhas destacadas e em condições de campo na cultura da soja, com a cultivar BMX Potencia RR. Os experimentos com folhas destacadas foram conduzidos em laboratório, já o experimento em campo foi conduzido na Fazenda Escola Capão da Onça na safra 2013/2014. O delineamento experimental para o experimento das folhas destacadas foi o inteiramente casualizado em esquema fatorial 7 (tratamentos) x 2 (aplicação ou não do produto em metade da mesma folha), com cinco repetições. No experimento em campo foi adotado o delineamento de blocos ao acaso com quatro repetições. Os tratamentos para os experimentos foram: 1 - testemunha; 2 - acibenzolar-S-metílico (Bion 500 WG); 3 - cálcio (Max Fruit); 4 - micronutrientes: cobre, manganês e zinco (Wert Plus); 5 - micronutrientes: manganês, zinco e molibdênio (V6); 6 - adubo NK (Hight Roots); 7 - Ascophyllum nodosum (Acadian) e 8 - azoxistrobina + ciproconazol (Priori XTRA®) com adição do adjuvante Nimbus. Foram avaliados, pelo método da folha destacada os indutores contra Phakopsora pachyrhizi, Sclerotinia sclerotiorum e Rhizoctonia solani. Não houve diferença dos tratamentos para P. pachyrhizi. Para S. sclerotiorum e R. solani houve diferença destacando-se o tratamento com A. nodusum e micronutrientes: cobre, manganês e zinco e manganês, zinco e molibdênio, respectivamente. No experimento no campo foram realizadas 4 aplicações dos indutores de resistência (estádios fenológicos V3, V6, R1 e R5.1) e duas do fungicida (estádios fenológicos R1 e R5.1). As variáveis avaliadas foram: severidade de míldio (Peronospora manshurica), oídio (Microsphaera diffusa), ferrugem asiática (P. pachyrhizi), doenças de final de ciclo (DFC), desfolha, componentes de rendimento, produtividade e germinação e sanidade das sementes colhidas. Com os dados de severidade calculou-se a área abaixo da curva do progresso das doenças (AACPD). Os produtos alternativos controlaram o míldio, mas não apresentaram efeito sobre o oídio, ferrugem asiática, DFC e desfolha. O tratamento com fungicida foi o único que controlou a ferrugem asiática, oídio, DFC e diminuiu a desfolha. Os componentes de rendimento da cultivar que foram afetados pelos tratamentos foram o número de vagens por planta e peso de mil grãos. O tratamento com o fungicida proporcionou a maior produtividade. A desfolha foi fortemente correlacionada com o PMG, ressaltando a importância da manutenção da área foliar para assegurar o enchimento de grãos. A germinação e sanidade de sementes foram afetadas pelos tratamentos foliares sendo os melhores tratamentos com adubo NK e com o fungicida.

Made available in DSpace on 2017-07-25T19:30:56Z (GMT). No. of bitstreams: 1 Nathaly Les.pdf: 1337962 bytes, checksum: 9d17bfec361a7df2173d76e06ebeb918 (MD5) Previous issue date: 2016-02-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Among the diseases found in soybeans and beans, those of particular note are fungi found in the soil, of which the most important are Fusarium solani and Rhizoctonia solani. Controlling these diseases is difficult; the use of fungicides applied to the aerial parts is ineffective and treating seeds with fungicides is the most widely used method. However, in order to reduce the environmental impact alternative disease control measures have been sought such as the use of biological products. Consequently, the objective of this study was to evaluate the effectiveness of different biological products in the control of soil fungi (F. solani and R. solani) in relation to plant vigor, germination and growth promotion in bean and soybean crops. The experiments were conducted in duplicate in the Applied Plant Pathology Group laboratories and in the greenhouse of the State University of Ponta Grossa (UEPG) in 2015. The experimental design was entirely randomized blocks with 10 treatments and 4 replicates. The treatments were as follows: 1 - control without inoculation;control with inoculation; 3 - Trichoderma asperellum (Quality); 4 - Trichoderma harzianum (Trichodermil); 5 - Trichoderma harzianum (Ecotrich); 6 - Coniothyrium minitans (Coniothyrium); 7 - Bacillus subtilis (Serenade); 8 - Bacillus pumilus (Sonata); 9 – thiophanate-methyl + fluazinam (Certeza); 10 - fludioxonil + metalaxyl-M (Maxim XL). The blotter test and tests of plant vigor and germination were performed in the laboratory. The following were evaluated in the greenhouse:the initial and final emergence of seedlings; pre and post-emergence damping-off; the lengths of roots and aerial parts; fresh and dry weight; and the incidence and severity of both fungi. It was concluded that the best treatment for all the evaluated parameters was fludioxonil + metalaxyl-M. Apart from this treatment, for some parameters as root length and shoot and reduction in the incidence and severity of diseases the treatments with thiophanate-methyl + fluazinam, and the biological products based on Bacillus were also found to be efficient. The treatments based on T. harzianum and C. minitans were inefficient in the tested conditions. / Dentre as doenças que incidem na cultura da soja e do feijão, se destacam as causadas por fungos do solo, sendo os principais deles Fusarium solani e Rhizoctonia solani. O controle dessas doenças é difícil, o uso de fungicidas aplicados na parte aérea é ineficaz, sendo o tratamento de sementes com fungicidas o método mais utilizado. Entretanto, com o intuito de diminuir o impacto ambiental, busca-se medidas alternativas de controle de doenças, como por exemplo, o uso de produtos biológicos. Com base nisso, o objetivo desse trabalho foi avaliar a eficácia de diferentes produtos biológicos no controle dos fungos de solo (F. solani e R.solani), no vigor, germinação e na promoção de crescimento nas culturas do feijão e da soja. Os experimentos foram conduzidos em duplicatas nos laboratórios do grupo de fitopatologia aplicada e na casa de vegetação da Universidade Estadual de Ponta Grossa (UEPG), no ano de 2015. O delineamento experimental utilizado foi o de blocos inteiramente aleatorizados, com 10 tratamentos e 4 repetições. Os tratamentos foram: 1- testemunha sem inoculação; 2- testemunha com inoculação; 3 – Trichoderma asperellum (Quality); 4 – Trichoderma harzianum (Trichodermil); 5 – Trichoderma harzianum (Ecotrich) ; 6 – Coniothyrium minitans (Coniothyrium); 7 – Bacillus subtilis (Serenade ); 8 – Bacillus pumilus (Sonata); 9 – tiofanato metílico + fluazinam (Certeza); 10 – fludioxonil + metalaxil-M (Maxim XL). No laboratório foram realizados o Blotter test e os testes de vigor de plântulas e germinação. Na casa de vegetação foram avaliadas a emergência inicial e final das plântulas, tombamento em pré e pós-emergência, comprimento da raiz e da parte aérea, massa fresca e seca e a incidência e severidade dos fungos. Concluiu-se que o melhor tratamento para todos os parâmetros avaliados foi o fludioxonil + metalaxil-M, e para alguns parâmetros como comprimento da raiz e parte aérea e redução na incidência e severidade das doenças, além desse, os tratamentos com tiofanato metílico + fluazinam e os produtos biológicos a base de Bacillus também se mostraram eficientes. Os tratamentos a base de T. harzianum e C. minitans foram ineficientes nas condições em que foram testados.

Submitted by Angela Maria de Oliveira (amolivei@uepg.br) on 2017-11-20T16:15:42Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Hamilton Edemundo Tullio.pdf: 1895693 bytes, checksum: 920f37d0cb15b99d397a4e3b5c49b55d (MD5) / Made available in DSpace on 2017-11-20T16:15:42Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Hamilton Edemundo Tullio.pdf: 1895693 bytes, checksum: 920f37d0cb15b99d397a4e3b5c49b55d (MD5) Previous issue date: 2017-09-06 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A preocupação da sociedade com o excessivo uso de agrotóxicos utilizados na agricultura, para o controle de doenças, gera uma grande demanda de pesquisas com métodos de controle ambientalmente menos agressivos. Dentre eles, destaca-se o controle biológico. O uso de relações antagônicas, exercidas por microrganismos, tais como: antibiose, competição, parasitismo, predação e a indução de resistência em plantas, oferece uma vasta gama de oportunidades para a utilização de microrganismos que, ainda, são pouco conhecidos como os microrganismos endofíticos. O objetivo do trabalho foi realizar um levantamento do potencial de controle biológico de bactérias endofitícas isoladas do cacau, para os patógenos de solo Fusarium solani, Rhizoctonia solani e Sclerotinia sclerotiorum e sua ação na promoção do crescimento radicular de plantas de soja. Foram avaliadas 22 bactérias endofíticas em relação a seu potencial antagônico in vitro, pelo método de cultivo pareado com os fitopatógenos, utilizando como parâmetros: a formação de halo de inibição exercido pelas bactérias, o tamanho da colônia do patógeno e a porcentagem de inibição do crescimento micelial do patógeno. Os parâmetros utilizados para avaliar o potencial de controle das bactérias endofíticas sobre fungos de solo e a promoção do crescimento radicular in vivo foram: a porcentagem de emêrgencia de plantas, a altura de plantas, a porcentagem de plantas anormais, a severidade de doença, o volume de raízes, as massas fresca e seca de raízes e das partes áerea e total das plantas. Foram encontrados 9 isolados (TCB 02, TCB 7, TCB 08, TCB 10, TCB 11, TCB 17, TCB 18, TCB 19 e TBC 20), que apresentaram mais de 75% de inibição para pelo menos um dos patógenos testados nos experimentos in vitro, demonstrando alto potencial antagônico. O isolado bacteriano TCB 10, identificado como Paenibacillus e o isolado bacteriano TCB 08, identificado como Staphylococcus apresentaram potencial antagônico para os três fitopatógenos. Os isolados TCB 17, TCB 18 e TCB 19 apresentaram potencial antagônico para S. sclerotiorum. Para os testes com o tratamento de sementes o isolado bacteriano TCB 10 apresentou redução da severidade de R. solani. Não se pôde concluir que as bactérias endofíticas realmente exerceram promoção do crescimento radicular nas plantas. / The society concern with the excessive use of agrochemicals in agriculture to control diseases generates great demand for research with environmentally less aggressive control methods, among them biological control. Utilizing antagonistic relations exerted by microorganisms such as antibiosis, competition, parasitism, predation and resistance induction in plants, offering a wide range of opportunities for the use of microorganisms that are still little known as endophytic microorganisms. The objective of this work was to investigate the biological control potential of endophytic bacteria isolated from cocoa against soil pathogens Fusarium solani, Rhizoctonia solani and Sclerotinia sclerotiorum and their action in promoting the root growth of soybean plants. Twenty-two endophytic bacteria were evaluated in vitro for their antagonistic potential by the culture method paired against phytopathogens, using as parameters: the formation of inhibition halo exerted by bacteria, the size of the pathogen colony and the percentage of inhibition of mycelial growth of the pathogen. The parameters used to evaluate the the control potential of endophytic bactéria on soil fungi and the promotion of root growth in vivo were: the percentage of plant emergence, plant height, percentage of abnormal plants, disease severity, root volume, the fresh mass and dry mass of roots, and the aerial and total part of the plants. There were 9 isolates (TCB 02, TCB 7, TCB 08, TCB 10, TCB 11, TCB 11, TCB 17, TCB 18, TCB 19 and TBC 20) that showed more than 75% inhibition for at least one of the pathogens tested in the experiments in vitro, demonstrating high antagonistic potential. The bacterial isolate TCB 10, identified as Paenibacillus and the bacterial isolate TCB 08, identified as Staphylococcus presented an antagonistic potential for the three phytopathogens. The isolates TCB 17, TCB 18 and TCB 19 presented antagonistic potential for S. sclerotiorum. For the tests with the seed treatment the bacterial isolate TCB 10 presented reduction of the severity of R. solani. It was not possible to conclude that the endophytic bacteria promoted the growth of roots in plants.

La qualité de présentation d'une pomme de terre de consommation, Solanum tuberosum L., commercialisée en produit frais est devenue une exigence et un enjeu économique significatif dans les relations commerciales. Compte tenu du mode de reproduction par voie végétative de cette espèce, ces exigences sont également imposées au tubercule de semence. Organe de réserve et de propagation, le tubercule est produit sous terre, ce qui l'expose aux microorganismes telluriques et le rend potentiellement porteur d'altérations superficielles dont l'origine n'est pas encore clairement identifiée pour certaines d'entre elles. L'objectif de ce travail est de recenser et de caractériser ces altérations superficielles du tubercule et d'en déterminer les causes. Après l'établissement d'une nomenclature et d'une classification consensuelles des défauts observables sur tubercule, deux hypothèses ont été formulées et testées: (1) les défauts sont d'origine pathogène et/ou (2) ils résultent d'une réponse de la plante à des stress environnementaux. L'évaluation de la première hypothèse a mené à l'identification d'une grande diversité de microorganismes vivant à la surface des tubercules altérés. Leur pouvoir pathogène a été testé par une série de tests biologiques. Ceux-ci ont permis de reproduire les défauts sur des tubercules néoformés et de vérifier les postulats de Koch pour le champignon Rhizoctonia solani responsable de la formation de sclérotes. Pour bon nombre d'autres défauts visuels, aucune relation claire entre un microorganisme et une altération n'a pu être établie. Une étude de la structure des communautés microbiennes de la géocaulosphère de tubercules, altérés ou non, a démontré que les communautés fongiques et bactériennes se comportaient selon des dynamiques différentes au cours de la culture et en fonction de l'état sanitaire du tubercule de semence mais aucune relation de causalité n'a pu être mise en évidence. Il a par contre été noté une augmentation de la population de R. solani autour des tubercules altérés. La diversité des isolats d’origine française et européenne associés aux altérations des tubercules a donc été caractérisée. Elle révèle l'existence de relations phylogénétiques indépendantes de l'origine géographique et du cultivar hôte et suggère l'existence de d'événements génétiques fréquents et d'un brassage génétique entre les populations de R. solani. Le test de la seconde hypothèse a consisté à rechercher une implication potentielle de différents facteurs abiotiques dans la formation des altérations superficielles. L'analyse d'une enquête menée auprès d'agriculteurs a mis en évidence l'implication du pH, de certaines pratiques culturales, de la sensibilité de cultivars et de conditions météorologiques particulières dans l'occurrence de certains défauts. Ce travail a permis de clarifier la nomenclature des altérations, de confirmer l'implication de R. solani dans l'apparition de certaines d'entre elles et d'envisager de nouvelles hypothèses quant à la formation de défauts suite à une réponse de la plante à un stress environnemental. Ainsi, une voie a été ouverte vers la résolution de la problématique posée par toute une filière professionnelle, responsable de la mise en marché d'un produit frais de grande consommation, et répondant aux exigences du marché en matière de présentation, qualité culinaire et, mode de production respectueux de l'environnement. / The visual quality of fresh potatoes, Solanum tuberosum, became a dominant criterion and a significative economical issue in potato market. According the vegetative reproduction of this species, requirements for visual quality are also needed for potato seed tubers. As an organ for reserve and propagation, the tuber grows underground and is in contact with soil-borne microorganisms, making it potentially exposed to blemishes, for the majority of which the origin is still unclear.The objective of this work is to make an inventory of those tuber blemishes, to characterize them and determine their causes. After the establishment of consensual nomenclature and classification of the blemishes, two hypotheses were formulated: (1) blemishes are due to pathogenic attacks and/or (2) they result from a response of the plants to environmental stresses. The assessment of the first hypothesis allowed identifying a wide diversity of microorganisms living on the blemished tuber surface. Their pathogenicity was tested by several biological assays that allowed producing blemishes on progeny tubers and fulfilling the Koch's postulates for the fungus Rhizoctonia solani causing sclerotia. For many other blemishes no clear relationship was established between a microorganism and a blemish. A study of the microbial structure of the geocaulosphere of tubers blemished or not, showed that bacterial and fungal communities adopted different dynamics during the growing season and according to the sanitary status of the seed tuber, but no causality link could have been drawn. On the other hand, an increase of R. solani population around blemished tubers was observed. The diversity of strains of R. solani originating from France and from Europe and associated to the blemished tubers was characterized. The phylogenetic relationships between the strains were independent of the geographical origin and of the host cultivar, thus the existence of frequent genetic events and genetic mixing between the populations of R. solani was suggested. Concerning the potential implication of different abiotic factors, a survey conducted with farmers showed the implication of soil pH, some cultural practices, including the choice of the susceptible cultivars and meteorological conditions on the occurrence of some blemishes. This work made clear the blemish nomenclature, confirmed the implication of R. solani in the occurrence of some blemishes and suggested new hypotheses concerning the occurrence of blemishes as a plant response to a stressful environment. Thus, a path was opened toward the resolution of the issue asked by all the potato community, responsible for the marketing of a mass consumption fresh product and answering to market requirements related to visual and culinary qualities and to environmental friendly modes of production.

Die Kartoffel, eines der wichtigsten Nahrungsmittel weltweit, wird unter anderem von dem Erreger Rhizoctonia solani Kühn befallen. Durch dieses Pathogen hervorgerufene Qualitäts- und Ertragsverminderungen können zu erheblichen ökonomischen Verlusten führen. Da derzeitig verfügbare Bekämpfungsmaßnahmen nur eine eingeschränkte Effektivität aufzeigen, sind alternative Bekämpfungsstrategien dringend notwendig. Der Einsatz resistenter Sorten stellt eine effektive, umweltfreundliche Alternative dar, jedoch ist derzeit nur wenig über die der Resistenz der Kartoffel gegenüber R. solani zugrundeliegenden Mechanismen bekannt. Ziel dieser Arbeit war es, Merkmale aufzufinden, die mit einer erhöhten Feldresistenz der Kartoffel gegenüber R. solani korrelieren und zukünftig als Marker in der Züchtung zur Einschätzung des Resistenzgrads von Sorten genutzt werden können. Auf der Grundlage von Feldversuchen wurden zwei Kartoffelgenotypen mit einem unterschiedlichen Grad der Feldresistenz gegenüber R. solani für vergleichende molekularbiologische und biochemische Analysen ausgewählt. Die Analyse des Expressionsniveaus ausgewählter Abwehrgene zeigte, dass die Kartoffelsorte mit geringerer Anfälligkeit ein konstitutiv höheres Expressionsniveau aufweist als die Sorte mit einer höheren Anfälligkeit. Im Gegensatz zur stärker anfälligen Sorte wurde in Wurzeln und Stängeln der weniger anfälligen Sorte kein erhöhtes Expressionsniveau der Abwehrgene infolge der Infektion mit R. solani festgestellt. Zudem wies die weniger anfällige Sorte höhere Gehalte an α-Chaconin and α-Solanin sowie Nicotiflorin auf. Anhand von in vitro Untersuchungen wurde ein wachstumshemmender Effekt dieser Komponenten auf R. solani festgestellt. Weiterhin wurde ein geringerer Gehalt an R. solani-DNA in den Wurzeln der weniger anfälligen Sorte determiniert. Demnach scheint eine geringere Anfälligkeit der Kartoffel gegenüber diesem Erreger mit einer höheren, präformierten pflanzlichen Immunabwehr korreliert zu sein. / Potato, the fourth most important food crop worldwide, is also target of many pests and microbial pathogens including the fungus Rhizoctonia solani Kühn. The infection of potato with this pathogen leads to considerable economic losses. The soil-borne nature, the formation of melanised sclerotia, and the limited efficacy of fungicides impair the control of this pathogen and strengthen the necessity for alternative control measures. A very effective alternative is the use of resistant cultivars. Quantitative differences in the degree of resistance of potato to R. solani have been repeatedly observed in the field. However, until now there is no information available regarding the underlying mechanisms contributing to the resistance level. This thesis aimed at revealing mechanisms in potato which contribute to the manifestation of a certain degree of field resistance to R. solani. Based on the screening of various potato genotypes in field trials, two potato cultivars distinctly differing in the level of resistance to R. solani were selected for further molecular and biochemical analyses. The cultivar with a higher degree of resistance showed higher constitutive expression of defence-related genes. In contrast to the less resistant cultivar, no distinct increase of the defence-gene expression level was detectable upon pathogen infection in this cultivar. Moreover, contents of the glycoalkaloids α-chaconine and α-solanine and of the flavonol nicotiflorin were higher compared to the less resistant cultivar. Using in vitro culture tests, a growth-reducing effect of these compounds on R. solani was confirmed. Concluding, a higher resistance of potato cultivars to R. solani seems to be related to a higher expression level of defence-related genes and to a higher content of plant secondary metabolites. This enhanced constitutive defence level resulted in a lower pathogen colonisation of the plant, thus contributing to a reduced disease severity in the field.

Expanding global populations, unequal food distribution and disease pressure suggest food poverty is increasing. Consequently, much attention is focussed on alternative natural methods in which to increase agricultural yield. Previously, it was observed that Trichoderma hamatum strain GD12 and its respective N-acetyl-β-D-Glucosamine mutant ∆Thnag:hph promoted plant biomass and fitness that, as a result, may provide a credible natural alternative to synthetic fertilisers. However, on a molecular level, the manner in which this is achieved has not been fully elucidated. In this thesis, I report the biofertiliser effect of GD12 and mutant ∆Thnag::hph once applied to autoclaved peat microcosms as sole applications. Furthermore, I demonstrate the biocontrol ability of GD12 when co-inoculated with Sclerotinia sclerotiorum or Rhizoctonia solani and reveal, that once mycelium co-inoculation has occurred, GD12 increase plant biomass and provide protection; whilst ∆Thnag::hph does not. Consequently, I challenged the biocontrol effects of Trichoderma metabolite extract where I validate that both Trichoderma wild type GD12 and mutant ∆Thnag::hph are incapable of suppressing pathogen growth. Subsequently, I characterised the up-regulated signatures associated with GD12 and ∆Thnag::hph using LC-MS techniques where unique compounds were discovered from each strain of Trichoderma. In conclusion, I provide evidence that N-acetyl-β-D-Glucosamine mutation bring about metabolomic changes that affect the fungal secretome which, in turn, alters plant phenotype, fitness and germination. Furthermore, I have shown that these effects are species specific and depend upon pathogen, plant and fungal properties. However, further investigations are needed to fully elucidate the compound(s) responsible for biocontrol and biofertilisation; especially plant-specific effects that take place as a consequence of fungal activity.

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.

Compost can suppress soilborne plant pathogens that cause significant damage on globally important food crops. However, reports of plant pathogen suppression are inconsistent likely because there are no established standards for feedstock material, application rate, and maturity age upon application. Excellent results can be achieved in greenhouse trials, but field applications are much less reliable. Disease suppression occurs through the activity of biocontrol organisms (direct antagonism), and general microbial competition. Biocontrol species are hypothesized to colonize the pile during the curing phase, but single species may not be as important as microbial consortia. Substrate composition during maturation may give rise to a suppressive microbial community. More research is needed to understand the relationships between feedstock, maturity, and production process on compost microbial ecology. The thesis had two main objectives: 1) identify biological indicators in compost that could (a) characterize maturity, process, and feedstock, and (b) predict disease suppression against R. solani, and 2) identify bacterial and fungal community composition and/or structure that is associated with suppression of soilborne disease. Rhizoctonia solani is a facultative saprophytic fungus and soilborne plant pathogen that attacks many globally important food crops and turfgrass. Prior research suggests that managing carbon quality and compost maturity will alter relative competition between biological control microbes and the R. solani pathogen. The pathogen is responsible for economic losses to organic vegetable production in Vermont and there are no available methods to manage the disease that meet organic certification. R. solani on radish was chosen as a model system given its global importance, competitiveness affected by carbon quality, and lack of disease management options for organic production. Compost samples were most abundant in the bacterial phyla Proteobacteria and Bacteroidetes, and known biocontrol species were not detected in abundance. Compost samples did not differ significantly in fungal community composition, suggesting a dominance effect from the native soil fungal community. Overall, anaerobic digestate and vermicompost were most suppressive against R. solani. Thermophilic composts were not very suppressive overall, though a specially made hardwood bark compost was comparable to the suppressiveness of vermicompost application. Ecoenzyme analysis was able to integrate information on environmental substrate composition, microbial nutrient acquisition, and microbial community metabolism, offering the best view of current ecological conditions in compost. Ecoenzyme analysis showed that the most suppressive composts, anaerobic digestate and vermicompost, were most nutrient limited. All compost samples were severely nitrogen (N) limited, and anaerobic digestate and vermicompost were severely limited in both N and phosphorus (P). The additional P limitation may support non-pathogenic species to outcompete R. solani. The key to disease suppression may lie in matching up the ecology of the plant pathogen with the ecology of biocontrol, which may be engineered in compost.

Orientador: Paulo Cezar Ceresini / Banca: Helvécio Della Coletta Filho / Banca: Celso Dornelas Fernandes / Banca: Antonio de Goes / Banca: Dilermando Perecin / Resumo: No início dos anos 90, o fungo Rhizoctonia solani emergiu como um patógeno importante associado à morte de pastagens do gênero braquiária na Colômbia. Inicialmente, esse estudo indicou que R. solani AG-1 IA predomina como patógeno associado à queima da folha da braquiária nos Llanos Colombianos. Para o estudo da estrutura genético-populacional do patógeno, um total de 198 isolados de R. solani AG-1 IA foram coletados de campos de B. brizantha cv. Toledo, de Brachiaria híbrido Mulato e do arroz. Os isolados foram genotipados usando dez loci microssatélites. Um sistema reprodutivo misto (reprodução sexuada e clones adaptados) caracterizou as populações de R. solani AG-1 IA que infectam a braquiária. A alta fração clonal e os desvios do equilíbrio de Hardy-Weinberg encontrados foram consistentes com o efeito Wahlund associado à mistura de populações. Padrões históricos de migração entre populações hospedeiro-distintas indicaram a origem provável das populações que infectam braquiária a partir de populações que infectavam arroz. Para determinar o efeito do estresse térmico na evolutibilidade para crescimento micelial, populações de R. solani AG-1 IA infectando braquiária ou arroz e R. oryzae-sativae do arroz, foram submetidas à temperatura ótima e de estresse (25 e 35°C). A herdabilidade para crescimento micelial sob condições de estresse foi considerada alta na população de R. oryzae-sativae do arroz, indicando que os patógenos têm potencial de adaptação à temperatura de 35°C / Abstract: In the early '90s, the fungus Rhizoctonia solani has emerged as an important pathogen associated with the death of Brachiaria pastures in the Colombian Llanos. Initially, this study indicated that R. solani AG-1 IA was the predominant pathogen associated with the leaf blight in the Colombian Llanos. To study the population genetic structure of the pathogen, a total of 198 isolates of R. solani AG-1 IA were collected from fields of B. brizantha cv. Toledo, Brachiaria Mulato hybrid and from rice. These isolates were genotyped using ten microsatellite loci. A mixed mating system (sexual reproduction and dispersal of adapted clones) characterized the populations of R. solani AG-1 IA infecting Brachiaria. The high clonal fraction and deviations from Hardy-Weinberg equilibrium found in three out of four populations were consistent with Wahlund effect associated with the mixing of populations. Historical patterns of migration between different host-populations indicated that the likely source of the current populations infecting Brachiaria in the Colombian Llanos was from populations that originally infected rice. To determine the effect of heat stress on the evolvability for mycelial growth, two host distinct populations of Rhizoctonia solani AG-1 IA infecting either brachiaria or rice and a rice-infecting population of R. oryzae-sativae, were submitted to optimal and stress temperatures (25°C and 35°C). The heritability values for mycelial growth under heat stress was considered high for rice-infecting population of R. oryzae-sativae, indicating that these pathogen's population have a high potential to adapt to 35°C temperature / Doutor