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.

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

Submitted by (lucia.rodrigues@ufrpe.br) on 2017-03-20T14:48:52Z No. of bitstreams: 1 Litervaldo Pereira Machado.pdf: 826962 bytes, checksum: 4c267bd8c50631dcb8bdf8b7b2c1cc47 (MD5) / Made available in DSpace on 2017-03-20T14:48:52Z (GMT). No. of bitstreams: 1 Litervaldo Pereira Machado.pdf: 826962 bytes, checksum: 4c267bd8c50631dcb8bdf8b7b2c1cc47 (MD5) Previous issue date: 2012-02-29 / Rhizoctonia canker, caused by Rhizoctonia solani, is an important cowpea disease in Northeastern region of Brazil. This thesis aimed: a) to evaluate the potential of crop rotation and green manures in inducing suppressiveness to Rhizoctonia canker in cowpea; b) to identify the biotic factors related to suppression; and c) to analysis the stability of the disease suppression by selected crop rotation in relation to different isolates and inoculum density of the pathogen, and soils from different locations. The experiments were conducted in microplots in the field. In relation to crop rotations, Initially, 14 treatments were compared in four growing seasons, including different combinations of cowpea (CA) in rotation with cotton (AL), sunflower (AL), castor bean (MA), corn (MI) and sorghum (SO), and in combination with fallow (PO) and cowpea monoculture. The rotations CA-MI-SO-CA, CA-GI-SO-CA and CA-MI-PO-CA provided reductions of 77.6%, 74.0% and 73.9% in the disease severity, respectively. When the stability of disease control by CA-MI-SO-CA rotation was evaluated in relation to different pathogen isolates, inoculum densities and soils, in all situations the disease severity was significantly (P0,0001) lower under crop rotation as compared to cowpea monoculture, indicating the potential of the crop rotation for controlling the Rhizoctonia canker. In relation to green manures, 13 treatments were compared in five growing seasons, considering different combinations of cowpea and green manures (sunn hemp, breviflora crotalaria, showy crotalaria, jack bean, velvet bean, dwarf mucuna, lablab bean, dwarf pigeon pea, forage pigeon pea, corn, millet and sorghum). For the two evaluations after green manures cultivation, the incorporation of sorghum into the soil led to smallest levels of severity of cowpea Rhizoctonia canker, reducing by 81.3% and 83.3% the disease severity. There was no significant correlation from levels of disease severity with microbiological variables. / A rizoctoniose, causada por Rhizoctonia solani, é uma importante doença do feijão-caupi na região Nordeste do Brasil. Essa tese teve como objetivos: a) avaliar o potencial da utilização de rotações de culturas e adubos verdes na indução da supressividade à rizoctoniose do feijão-caupi; b) identificar os possíveis fatores bióticos dos solos responsáveis pela supressividade; e c) analisar a estabilidade do controle pela rotação de cultura selecionada em relação a diferentes isolados e densidades de inóculo do patógeno, bem como solos de diferentes localidades. Os experimentos foram realizados em microparcelas no campo. Em relação à rotação de culturas, inicialmente foram comparados 14 tratamentos em quatro ciclos de cultivo, incluindo diferentes combinações de feijão-caupi (CA) em rotação com as culturas de algodão (AL), girassol (GI), mamona (MA), milho (MI) e sorgo (SO), bem como em combinação com pousio (PO) e feijão-caupi em monocultura. As rotações CA-MI-SO-CA, CA-GI-SO-CA e CA-MI-PO-CA propiciaram reduções na severidade da doença de 77,6%, 74,0% e 73,9%, respectivamente. Quando avaliada a estabilidade do controle da doença pela rotação CA-MI-SO-CA a diferentes isolados, densidades de inóculo e solos, em todas as situações a severidade foi significativamente inferior (P0,0001) sob a rotação de culturas comparada à monocultura, indicando o potencial de utilização da rotação no controle da rizoctoniose. Em relação aos adubos verdes, foram comparados 13 tratamentos, considerando diferentes combinações de feijão-caupi e adubos verdes (crotalária breviflora, crotalária juncea, crotalária spectabilis, feijão-de-porco, guandu anão, guandu forrageiro, labe-labe, mucuna anã, mucuna preta, milho e sorgo), em cinco ciclos de cultivo. Nas duas avaliações realizadas após o cultivo de adubos verdes, a incorporação de sorgo ao solo propiciou os maiores níveis de controle da doença, reduzindo em 81,3% e 83,3% a severidade. Não houve correlação significativa dos níveis de severidade da rizoctoniose com as variáveis microbiológicas avaliadas nos solos.

Submitted by (lucia.rodrigues@ufrpe.br) on 2017-03-21T14:50:39Z No. of bitstreams: 1 Marcelo Garcia de Oliveira.pdf: 229150 bytes, checksum: cb960836d78efca26b86c65b585f44af (MD5) / Made available in DSpace on 2017-03-21T14:50:39Z (GMT). No. of bitstreams: 1 Marcelo Garcia de Oliveira.pdf: 229150 bytes, checksum: cb960836d78efca26b86c65b585f44af (MD5) Previous issue date: 2011-02-25 / The Rhizoctonia canker, caused by Rhizoctonia solani, is an important disease of cowpea in northeastern Brazil. This work aimed to select cowpea rhizobacteria as biocontrol agents of Rhizoctonia canker and to assess the stability of the control by promising isolates for different isolates and inoculum densities of the pathogen, and soil types. Samples of cowpea plants with no symptoms of root diseases were collected in 22 fields and 87 bacterial isolates were obtained from their rhizoplane, with 59 strains of Bacillus spp. and 28 strains of fluorescent Pseudomonas spp. These strains were evaluated for their efficacy in reducing the severity of Rhizoctonia canker of cowpea under greenhouse conditions. In a preliminary screening cowpea seeds (cv. IPA-206) were immersed in bacterial suspension(approximately 108 cells/mL) prepared in 0.1 M MgSO4 solution and sown in trays containing unsterilized soil (Camaragibe) previously infested (isolated CMM-2656) with 150 mg of substrate (rice) colonized/kg soil. The assessment of disease severity was determined after 15 days, using a scale from 0 to 4, where 0 = no symptoms and 4 = non-germinated seeds and/or non-emerged plantlets. Only five bacterial strains (B-05, B-13, B-63, B-65 and B-71), all from the genus Bacillus, reduced levels of disease severity above 45% and were evaluated in relation to five isolates (CMM-2651, CMM-2654, CMM-2666, CMM-2675 and CMM-2682) and three inoculum densities (200, 250 and 300 mg/kg soil) of R. solani, and five soil types (Aldeia, Goiana, Itapirema, Pombos and Vitória). Only the bacterial strain B-71 showed similar levels of Rhizoctonia canker control induced by different isolates of the pathogen, with an average of 24.5% in the reduction of severity levels. The strain B-65 had the highest levels of disease control at the three inoculum densities of R. solani, with an average of 22.2%. It was evident the influence of soil on the effectiveness of the strains. The great variability of results in the control of Rhizoctonia canker due to different isolates and inoculum densities of R. solani as well as the unstable response in different soil types may be factors limiting the use of Bacillus spp. in the treatment of cowpea seeds in field conditions. / A rizoctoniose, causada pelo fungo Rhizoctonia solani, é uma importante doença do caupi no Nordeste brasileiro. Esta dissertação teve como objetivos efetuar a prospecção de rizobactérias de caupi como agentes de biocontrole da rizoctoniose e avaliar a estabilidade do controle por isolados promissores em relação a diferentes isolados e densidades de inóculo do patógeno, e tipos de solos. Foram efetuadas coletas de plantas de caupi sem sintomas de doenças radiculares em 22 áreas de plantio. Destas plantas, foram obtidos 87 isolados bacterianos do rizoplano, sendo 59 isolados de Bacillus spp. e 28 isolados de Pseudomonas spp. do grupo fluorescente. Esses isolados foram avaliados quanto à eficácia na redução da severidade da rizoctoniose do caupi em casa de vegetação. Na seleção preliminar, sementes de caupi (cv. IPA-206) foram imersas nas suspensões bacterianas (aproximadamente 108 células/mL) preparadas em solução de MgSO4 0,1M e semeadas em bandejas contendo solo não esterilizado (Camaragibe) previamente infestado com o patógeno (isolado CMM-2656), na densidade de 150 mg de substrato (arroz) colonizado/kg de solo. A avaliação da severidade da doença foi efetuada após 15 dias, utilizando-se escala de notas de 0 a 4, onde 0 = sem sintomas e 4 = sementes não germinadas e/ou plântulas não emergidas. Somente cinco isolados bacterianos (B-05, B-13, B-63, B-65 e B-71), todos do gênero Bacillus, propiciaram níveis de redução da severidade da doença superiores a 45% e foram avaliados em relação a cinco isolados (CMM-2651, CMM-2654, CMM-2666, CMM-2675 e CMM-2682) e três densidades de inóculo (200, 250 e 300 mg/kg de solo) de R. solani, bem como cinco tipos de solos (Aldeia, Goiana, Itapirema, Pombos e Vitória). Somente o isolado bacteriano B-71 apresentou níveis similares de controle da rizoctoniose induzidos pelos diferentes isolados do patógeno, com redução média de 24,5% nos níveis de severidade. O isolado bacteriano B-65 apresentou os maiores níveis de controle da doença nas três densidades de inóculo de R. solani, com média de 22,2%. Ficou evidente a influência do solo na eficácia dos isolados bacterianos. A grande variabilidade dos resultados no controle da rizoctoniose em função dos diferentes isolados e densidades de inóculo de R. solani, assim como da resposta instável em diferentes tipos de solos, podem ser fatores limitantes à utilização dos isolados de Bacillus spp. no tratamento de sementes de caupi em condições de campo.

Fungi in the genus Trichoderma have been characterized as biocontrol agents of plant pathogens since the 1930s. The use of biologicals for disease management has increased in recent years, typically marketed as a safer alternative to chemical applications. However, biologicals often lack consistent control across varying environmental conditions. To overcome the loss in efficacy due to environmental conditions, biologicals can be combined with common fungicide seed-treatments to provide improved control. Additionally, the presence of a biological organism could slow the development of a pathogen population. Greenhouse trials were conducted to determine the baseline root colonization of three Trichoderma spp. used in conjunction with five commonly used seed treatments. In field trials, a stand-alone treatment of the Trichoderma isolates was assessed for management of Rhizoctonia root rot (caused by Rhizoctonia solani) and frogeye leaf spot (caused by Cercospora sojina). The greenhouse trial provided evidence that isolates of T. virens and T. hamatum can colonize the roots of plants in which seeds were treated with metalaxyl + prothioconazole + penflufen or metalaxyl + prothioconazole + penflufen + fluopyram. Surprisingly, in the Rhizoctonia root rot trials, the soybean seedlings treated with Trichoderma spp. had significantly reduced stand compared to the R. solani inoculated control. For the frogeye leaf spot trial, an application of T. virens conidial suspensions as a foliar treatment significantly (P ≤ 0.10) reduced frogeye leaf spot severity of soybean compared to a non-treated control. Future research is warranted to better understand the potential efficacy in additional environments and the mechanism(s) of action used by the Trichoderma isolates evaluated in these experiments.

Typescript. / Includes bibliographical references. / 193 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Pathology, 1965

Three pages of addenda pasted inside back cover. Bibliography: leaves 166-189. Rhizoctonia solani is a complex species comprising morphologically basidiomycetous imperfect fungi. This study aimed to determine genetic diversity within R. solani AG-3 causing rhizoctonia disease of potato in South Australia. For this purpose, pectic zymogram, PCR, DNA fingerprinting and RFLP techniques were used in conjunction with traditional plant pathology procedures.

Il est encore difficile de prédire et de contrôler le développement des maladies telluriques qui sont à l'origine de nombreux dégâts dans les systèmes de culture. Ce travail interdisciplinaire en épidémiologie a pour objectif de comprendre et de modéliser le développement spatio-temporel des épidémies telluriques afin d'identifier des leviers de gestion pour ces maladies. En se basant sur le pathosystème betterave sucrière - Rhizoctonia solani, la thèse se focalise sur trois problèmes. Dans un premier temps, en alliant mesures expérimentales de la dispersion du pathogène et simulations d'un modèle stochastique spatialement explicite, nous montrons que la croissance de l'hôte peut induire un changement dans le comportement du système qui, dans certains cas, devient invasif alors qu'il était initialement non-invasif. Dans un second temps, sur la base de mesures expérimentales nous proposons un modèle âge-dépendant de la distribution de la période d'incubation qui est utilisé pour relier les infections cachées et les observations de maladie. Le comportement cryptique des épidémies est ensuite étudié par simulation d'un modèle spatial hiérarchique qui intègre la période d'incubation. Dans un troisième temps, un modèle spatialement implicite est utilisé pour estimer les taux d'infection à partir de données temporelles de maladie et pour analyser les effets de la biofumigation sur les épidémies. Ces paramètres sont ensuite utilisés pour prédire le développement stochastique des épidémies à partir d'un modèle spatial individu-centré. Les résultats confirment que la biofumigation ne permet qu'un contrôle partiel des épidémies mais suggèrent que ce contrôle biologique diminue l'incertitude autour du développement cryptique de la maladie. Pour finir, les résultats de ces travaux sont discutés et les perspectives qu'ils suscitent sont présentées.

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