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.

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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In this study, we have demonstrated that inoculation of bean seeds with non-pathogenic binucleate Rhizoctonia (np-BNR) at sowing protected bean seedlings from infection of R. solani. Using quantitative real-time RT-PCR (QRT-PCR), transcript levels of defense genes encoding 1,3-beta-glucanase (GLUC), phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) in one-week old bean seedlings was monitored during np-BNR and R. solani interaction. The results revealed that protection effect of np-BNR correspond to a systemic suppression of these three defense genes' expression from significant higher level elicited by R. solani to the level of non-infected plants. This indicates that bio-protection by np-BNR isolates is not correlated to activation of these three defense genes' expression. Similar suppression was achieved for pre-colonization of bean seedlings with arbuscular mycorrhizal (AM) Glomus introradices on GLUC gene expression, although the AM fungus did not significantly reduce rot symptoms. Possible mechanisms implicated in down-regulation during plant-pathogen and np-BNR or AM interaction are discussed.

Rhizoctonia solani (AG-3), the causal agent of Rhizoctonia disease of potato, overwinters as sclerotia on potato tubers. To develop a biocontrol strategy based on the prevention of the sclerotial germination, an isolation of microorganisms colonizing sclerotia of infected potato tubers (cultivars Norland, Atlantic and Souris), was conducted. In vitro screening was used to select effective antagonistic fungi against Rhizoctonia solani. Fifty fungal isolates were selected in order to cover all identified genera and potato variety and examined for their ability to inhibit germination of sclerotia which were incubated with the test fungus for 14 days. Twenty-four (24) fungal isolates were retained based on their ability to reduce sclerotial viability by more than 50% as compared with 100% viability of untreated sclerotia. These 24 isolates were further examined for their ability to protect Table beet seedlings against the pathogen in greenhouse soils. Based on their ability to protect Table beet seedlings from Rhizoctonia infections and to increase the number of secondary roots and root length isolates, F2, F11, F132, F158, and F258 were screened and test their efficacy to increase beet seed germination in field soils. (Abstract shortened by UMI.)

Tobacco phylloplanins (T-phylloplanin) are a group of closely-related glycoproteins that are formed and disposed at the interface between the plant aerial surface (the phylloplane) and the atmosphere. They are synthesized in short procumbent trichomes and are secreted to aerial surfaces where they are thought to serve the plant as a first line of defense against fungal pathogens. Here it is shown using in vitro and in planta assays that tobacco and sunflower phylloplanins have broad-spectrum antifungal activities against spores - and also hyphae for two species - of several true fungi. Field tests show that T-phylloplanin reduces diseases caused by three important fungal pathogens of turf grasses. Tobacco phylloplanins are distinct proteins but they have properties in common with small, membrane-pore-forming, antimicrobial peptides formed by other organisms. To directly determine if T-phylloplanin has pore-forming activity we monitored conductivity change and specific ion leakage from spores and hyphae in suspension. Results indicate that phylloplanin causes fungal membrane disruption that leads to ion depletion and cell death. Having observed broad efficacy of T-phylloplanin against spores and/or hyphae of several true fungi, but no activity towards hyphae of the oomycetes, Pythium and Peronospora parasitica, we tested for possible effects on zoospores of the latter two pathogens. T-phylloplanin was shown to be effective against their zoospores, extending the efficacy of T-phylloplanin to include water molds. In the course of these experiments we also tested the effects of the diterpene cis-abienol that is secreted from tall trichomes of tobaccos and found this compound impacted zoospores and could prevent black shank disease caused by P. parasitica when applied to soil-grown tobaccos as a root drench. Thus, results of these studies with phylloplanins and cis-abienol, two different tobacco surface accumulated compounds are consistent with their serving the plant as first line of defense systems against a wide array of invading fungal pathogens. Phylloplanins and cis-abienol may be useful for controlling fungal diseases in tobacco float beds. The efficacy shown here for T-phylloplanin control of fungal pathogens of turf grasses in the field suggests that this natural product may find use in IPM of turf and other crops.

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.