As rizobacterias promotoras do crescimento de plantas (RBCP) colonizam as raízes de plantas e induzem um aumento no crescimento vegetal por diversos mecanismos. A rizobacteria Bacillus subtilis é capaz de atuar como agente de controle de doenças de várias plantas cultivadas, como também promotor de crescimento vegetal. Diante disso, este trabalho teve como objetivos, nos quatro capítulos apresentados, de avaliar o crescimento micelial de patógenos, com a capacidade dos isolados de B. subtilis em inibir esses patógenos; avaliar a capacidade dos isolados de B. subtilis, inoculados em solo adubado com fosfato natural e sem adubação, em disponibilizar P e no crescimento da soja e feijão caupi em condições de casa de vegetação; avaliar a eficiência da inoculação de B. subtilis como promotor de crescimento vegetal na cultura do milho, em casa de vegetação; e avaliar a eficiência da inoculação de B. subtilis no desempenho agronômico da soja em condições de campo em duas localidades. Foram testados sete isolados de B. subtilis contra os patógenos Fusarium subglutinans, Curvularia lunata e Bipolaris spp., avaliando a capacidade de controle biológico in vitro. Na avaliação da capacidade de inibição do crescimento dos patógenos utilizando quatro métodos os isolados de B. subilis UFTBs 03, UFTBs 05, UFTBs 06, UFTBs 07 foram eficazes. Os isolados UFTBs 01, UFTBs 03, UFTBs 04, UFTBs 05, UFTBs 06 e UFTBs 07 foram capazes de inibir o crescimento micelial dos patógenos testados por metabólitos termoestáveis, sendo a antibiose seu principal mecanismo de ação. Quanto à eficiência da inoculação de B. subtilis em soja e feijão caupi com adubação de fosfato natural e sem adubação, em casa de vegetação, utilizando sete isolados e um MIX, observou-se que a maioria dos tratamentos onde recebeu a inoculação de B. subtilis proporcionou o crescimento da cultura da soja e do feijão caupi, também a maioria do isolados testados proporcionaram um maior teor de P disponível no solo e na parte aérea das plantas, tanto em solo suplementado com fosfato natural como também em solo sem adubação, em ambas as culturas. Em casa de vegetação testando inoculante de B. subitilis, composto por três cepas (UFTBs 01, UFTBs 02, UFTBs 03), em milho, mostrou que sementes de milho inoculadas com B. subtilis resultaram em plantas com maior acúmulo de biomassa, em estádio inicial de crescimento. No experimento de campo, onde foi testado inoculante de B. subtilis, composto por três cepas (UFTBs 01, UFTBs 02, UFTBs 03), na cultura da soja em duas localidades na safra 2013/1014, a inoculação com B. subtilis proporcionou aumento da biomassa e produtividade da soja nas duas regiões onde foram avaliadas. Os resultados do presente trabalho comprovam a eficiência de B. subtilis nativos, isolados de solos do Tocantins, no controle biológico de fitopatogênos, bem como a capacidade como promotores de crescimento de feijão caupi, milho e soja, e aumento de produtividade da cultura da soja. / The rhizobacteria promote plant growth (RBCP) colonize roots of plants and induce an increase in plant crecimento by different mechanisms. The rizobacteria Bacillus subtilis is able to act as a control agent of several cultivated plant diseases, as well as plant growth promoter. Thus, this study aimed to the four chapters presented, to evaluate the mycelial growth of pathogens such as the ability of isolates of B. subtilis to inhibit these pathogens; evaluate the effect of isolates of B. subtilis inoculated in soil fertilized with rock phosphate and without fertilization, as its ability to provide P, the growth of soybean and cowpea at home conditions of vegetation; evaluate the efficiency of B. subtilis inoculation as plant growth promoter in corn in a greenhouse; and evaluate the efficiency of inoculation of B. subtilis the agronomic performance of soybeans under field conditions in two locations. They tested seven isolates of B. subtilis pathogens Fusarium subglutinans, Curvularia lunata and Bipolaris spp., assessing the biological control capacity in vitro. In the evaluation of growth inhibition ability of the pathogens using four methods isolates of B. subilis UFTBs 03, UFTBs 05, UFTBs 06, UFTBs 07 were effective. Isolated UFTBs 01, UFTBs 03, UFTBs 04, UFTBs 05, UFTBs 06 and 07 UFTBs were able to inhibit the mycelial growth of the pathogens tested by thermostable metabolites, antibiose being its main mechanism of action. As the efficiency of inoculation of B. subtilis in soybean and cowpea with natural phosphate fertilizer and no fertilization in a greenhouse, using seven isolates and MIX, it was observed that most of the treatments which received inoculation of B. subtilis provided the growth of soybean and cowpea, also most of the isolates tested provided a higher P content available in soil and shoots of plants, both in soil supplemented with rock phosphate as well as in soil fertilization in both cultures. In greenhouse testing inoculant B. subitilis, composed of three strains (UFTBs 01, UFTBs 02, UFTBs 03) in corn, showed that maize seed inoculated with B. subtilis resulted in plants with higher biomass accumulation in stadium initial growth. In the field trial, where he was tested inoculant B. subtilis, composed of three strains (UFTBs 01, UFTBs 02, UFTBs 03) in soybean at two sites in the harvest 2013/1014, inoculation with B. subtilis gave rise biomass and soybean yield in the two regions where they were evaluated. The results of this study demonstrated the efficacy of B. subtilis native isolated from the Tocantins soil, the biological control of plant pathogens, as well as the capacity and bean growth promoters cowpea, corn and soybeans, and increased the soybean yield.

Rizobactérias são agentes muito importantes para a promoção do crescimento de plantas em razão da produção de metabólitos. Dentre estas rizobactérias, as Streptomyces apresentam grande potencial em produzir diversos compostos bioativos. Desse modo, o presente trabalho teve como objetivos, nos três capítulos apresentados, caracterizar morfologicamente isolados de Streptomyces spp., avaliar a solubilização de fosfato e a produção de ácido indol acético (AIA), a compatibilidade entre Streptomyces spp. e Bradyrhizobium japonicum e a atividade antagônica aos fungos patogênicos Curvularia lunata e Colletotrichum sp. Além disso, objetivou selecionar isolados de Streptomyces spp., para serem utilizadas como inoculantes tanto para a cultura da soja como para a cultura do feijão-caupi na região e avaliar o efeito das doses sobre as culturas. Os resultados obtidos indicaram que os isolados de Streptomyces apresentaram características fenotípicas variadas, sendo que o isolado UFT-St07 apresentou índice de solubilização de fosfato. Em relação à produção de ácido indol acético, os melhores resultados foram obtidos na presença do indutor L-triptofano, e os melhores isolados observados foram UFT-St04 e UFT-St08. Quanto à compatibilidade entre Streptomyces spp. e o inoculante B. japonicum, observou-se que os maiores índices de inibição foram observados com os isolados UFT-St01 e UFT-St09. Os isolados UFT-St05 e UFTSt07 apresentaram efeito positivo no biocontrole de Curvularia lunata., e os isolados UFT-St04 e UFT-St07 no biocontrole de Colletotrichum sp. Quanto à utilização de Streptomyces na cultura da soja melhores resultados foram observados com o isolado UFT-St07. No experimento em campo as diferentes dosagens de inoculante mostraram-se eficientes na manutenção do estande final de plantas, sendo que a melhor dose do MIX de Streptomyces (UFT-St03, UFT-St06 e UFT-St08) foi de 300 mL para cada 50 kg de semente. Quanto à cultura de feijão, a estirpe UFT-St03 foi a que apresentou melhores resultados. Além disso, as melhores doses de inoculante foram de 300 e 400 mL/50 kg sementes para todos os parâmetros avaliados. Dessa forma, foi possível observar que as Streptomyces tem potencial no biocontrole de fungos fitopatogênicos e podem ser utilizadas como biofertilizante por apresentarem potencial no crescimento e incorporação de biomassa, além de favorecer a produtividade. / Rhizobacteria are very important agents for the promotion of plant growth due to the production of metabolites. Among these rhizobacteria, Streptomyces have great potential in producing several bioactive compounds. The objective of this work was to characterize morphologically isolated Streptomyces spp., to evaluate phosphate solubilization and the production of indole acetic acid (IAA), the compatibility between Streptomyces spp. and Bradyrhizobium japonicum and the antagonistic activity to the pathogenic fungi Curvularia lunata and Colletotrichum sp. In addition, the objective was to select isolates of Streptomyces spp. to be used as inoculants for both soybean and cowpea culture in the region and to evaluate the effect of the doses on the crops. The results showed that the isolates of Streptomyces presented varied phenotypic characteristics, and the isolate UFT-St07 presented index of phosphate solubilization. Regarding the production of indole acetic acid, the best results were obtained in the presence of the L-tryptophan inducer, and the best isolates observed were UFT-St04 and UFT-St08. Regarding the compatibility between Streptomyces spp. and inoculant B. japonicum, it was observed that the highest inhibition indices were observed with the isolates UFT-St01 and UFT-St09. The UFT-St05 and UFTSt07 isolates showed a positive effect on the biocontrol of Curvularia lunata, and the isolates UFT-St04 and UFT-St07 in the biotype of Colletotrichum sp. Regarding the use of Streptomyces in the soybean crop, better results were observed with the isolate UFT-St07. In the field experiment the different dosages of inoculant were efficient in maintaining the final plant stand, and the best dose of Streptomyces MIX (UFT-St03, UFT-St06 and UFT-St08) was 300 mL for every 50 kg of seed. Regarding the bean culture, strain UFT-St03 was the one that presented the best results. In addition, the best inoculant doses were 300 and 400 mL / 50 kg seeds for all parameters evaluated. Thus, it was possible to observe that Streptomyces has potential in the biocontrol of phytopathogenic fungi and can be used as biofertilizer because they have potential in the growth and incorporation of biomass, besides favoring productivity.

O estado de Tocantins tem despontado no cenário nacional como um grande produtor de soja. Entretanto, várias são os fatores que contribuem para a redução da produtividade da soja e dentre os principais estão as perdas por doenças e diminuição do estande de plantio. A utilização do controle biológico constitui uma estratégia de grande interesse e importância para viabilizar a redução ou substituição do uso de defensivos. Fungos como o Trichoderma e o Purpureocillium são importantes antagonistas no solo contra doenças radiculares e nematoides fitopatogênicos. Diversos produtos à base de Trichoderma e Purpureocillium são comercializados em todo mundo. Desse modo, objetivou se com o presente trabalhar avaliar os efeitos da inoculação de Trichoderma e Purpureocillium na cultura da soja em diferentes regiões (Gurupi, Porto Nacional, Alvorada e Crixas) em Tocantins. Os experimentos foram conduzidos em condições de campo nas diferentes cidades produtoras de soja no Tocantins, utilizando os produtos TrichoPlus e TrichoMix formulados a base de Trichoderma (Trichoderma asperellum UFT 201) e Purpureocillium lilacinum e com diferentes doses, visando o biocontrole para manutenção de estande e consequentemente aumento de produtividade. A inoculação de Trichoderma e Purpureocillium presentes nos produtos TrichoPlus e TrichoMix influenciaram positivamente a manutenção de estande, a produtividade da soja e auxiliou na promoção de crescimento em todos os locais avaliados. Em Gurupi, no experimento I e II, tanto a aplicação isolada de Trichoderma (TrichoPlus) como a aplicação conjunta de Trichoderma e Purpureocillium (TrichoMix) promoveram incrementos na manutenção de estandes e maiores valores de produtividade em relação aos demais tratamentos. Em Porto Nacional, a inoculação dos produtos TrichoPlus e TrichoMix influenciaram positivamente a manutenção de estande e a produtividade das cultivares de soja de ciclos precoce, intermediária e tardio. Em Alvorada, a inoculação de Trichoderma (TrichoPlus) em soja de primeiro e segundo ano aumentaram o índice de sobrevivência de plantas, embora não tenha tido efeito significativo na produtividade. Em Crixas, a inoculação de Trichoderma (TrichoPlus) promoveu incrementos na manutenção de estandes e maiores médias de produtividade. O uso de microrganismos como agentes de biocontrole de doenças de plantas, apesar de muito estudado ultimamente, ainda precisa ser melhor compreendido, para alcançarmos sua eficiência ideal. / The state of Tocantins has been standing out in Brazil as a big soybean producer. However, there are many factors that contribute for the reduction of soybean productivity; the main ones are: losses due to diseases and decrease of planting booth. The utilization of biological control constitutes an interesting and important strategy to enable the reduction or substitution of the use of pesticides. Fungi such as Trichoderma and Purpureocillium are important antagonists, in soil, against root diseases and phytopathogenic nematodes. Several products based on Trichoderma and Purpureocillium are worldwide commercialized. Thus, this study aimed to evaluate the effects of the inoculation of Trichoderma and Purpureocillium on soybean crop at different regions (Gurupi, Porto Nacional, Alvorada and Crixás) in Tocantins. The experiments were performed under field conditions at different cities, which produce soybean in Tocantins, using the products TrichoPlus and TrichoMix formulated based on Trichoderma (Trichoderma asperellum UFT 201) and Purpureocillium lilacinum at different dosages, aiming biocontrol for booth maintenance, and thus, also aiming increase in productivity. The inoculation of Trichoderma and Purpureocillium present in the products TrichoPlus and TrichoMix influenced positively the booth maintenance, soybean productivity and helped the growth promotion at all places assessed. In Gurupi, in experiments I and II, not only the isolated application of Trichoderma (TrichoPlus) but also the joint application of Trichoderma and Purpureocillium (TrichoMix) promoted increases in booth maintenance and higher productivity values in relation to other treatments. In Porto Nacional, the inoculation of products TrichoPlus and TrichoMix influenced positively the booth maintenance and productivity of precocious, intermediate and late soybean cultivars. In Alvorada, the inoculation of Trichoderma (Trichoplus) in soybean of first and second year increased the survival index of plants, but did not affect significantly the productivity. In Crixás, the inoculation of Trichoderma (Trichoplus) promoted increases in booth maintenance and also higher productivity values. The use of microorganisms as biocontrol agents of plant diseases, despite being more studied lately, still need to be better comprehended, in order to achieve its optimal efficiency.

O guaraná, Paullinia cupana var. sorbilis, espécie nativa do Brasil é uma cultura de relevância para o país, principalmente nos estados da Bahia e Amazonas. O fruto contém substâncias estimulantes, como a cafeína, que conferem ao guaraná um grande potencial exploratório, visto que esta é uma das substâncias estimulantes mais consumidas no mundo. Apesar de sua importância, a cultura do guaraná é pouco estudada, portanto pouco se sabe sobre sua genética e as interações microbianas existentes, tanto em relação aos microrganismos endofíticos e epifíticos, quanto em relação aos patógenos. De tal forma que a cultura do guaraná na região Amazônica vem sendo afetada por condições fitossanitárias desfavoráveis, como a presença do fungo do gênero Colletotrichum, causador da antracnose, doença considerada uma ameaça à produção comercial do guaraná. Assim, visando compreender a dinâmica envolvida na interação planta - microrganismos e o possível controle da antracnose, o presente trabalho acessou a comunidade bacteriana associada às folhas com e sem sintomas de antracnose, de forma independente e dependente de cultivo; bem como, investigou o potencial biotecnológico e de biocontrole dos isolados bacterianos. A comunidade bacteriana acessada de forma dependente e independente de cultivo apresentaram similaridades, como maior valor de riqueza e menor diversidade bacteriana em folhas assintomáticas, quando comparadas com folhas sintomáticas, e com relação ao filo Proteobacteria, mais abundantemente acessado nas duas comunidades. Comparações realizadas com isolados bacterianos acessados epi e endofiticamente de folhas com e sem sintoma da antracnose apontaram que o aparecimento da doença antracnose na folha pareceu ser o fator que mais influenciou na estrutura da comunidade bacteriana. Com relação às diferenças entre tecidos sintomáticos e assintomáticos, foi possível identificar alguns gêneros abundantes mais frequentemente acessados em plantas sintomáticas, sendo que os gêneros Pseudomonas, Stenotrophomonas e Pantoea foram acessados em grande frequência tanto de forma dependente como independente de cultivo. Porém, de forma independente de cultivo foram acessados outros táxons abundantes que diferiram significativamente entre as plantas, sendo que folhas sintomáticas apresentaram Acinetobacter, Acidobacter_GP1 e Sphingobacteria, e em folhas assintomáticas foram acessados os táxons Methylobacterium, Beijerinckia, Bacilli e um grupo de Rhizobiales não classificados. Além disto, os microrganismos endofíticos e epifíticos cultivados foram testados com o fitopatógeno Colletotrichum sp. em ensaios de antagonismos, sendo que isolados do gênero Bacillus, Stenotrophomonas, Pantoea, Erwinia, Entereobacter, Pseudomonas, entre outros, apresentaram inibição do crescimento do fungo fitopatogênico. As bactérias cultivadas ainda foram testadas quanto ao potencial biotecnológico de produção de enzimas hidrolíticas e sideróforo. Muitos isolados apresentaram produção de protease e sideróforo. Foi possível também correlacionar a produção das enzimas amilase, lipase e poligalacturanase com os isolados provenientes de tecidos sintomáticos. / Guarana, Paullinia cupana var. sorbilis, is a native culture of Brazil that has relevance to the country, mainly in the states of Bahia and Amazonas. The fruit contains stimulants substances, such as caffeine, that gives a high exploration potential to the culture, since this is one of the most consumed stimulant substance in the world. Despite its importance, the culture of guarana hasnt gotten much of attention, and little is known about its genetics and microbial interactions with both epiphytic and endophytic microorganisms, and in relation to pathogens. So, the guarana culture in the Amazon region has been affected by bad phytosanitary conditions, such as the presence of the fungi Colletotrichum, which causes anthracnose disease thats considered a threat to guarana commercial production. Thus, to understand the dynamics involved in the interaction plant-microorganism and the possible control of anthracnose, this study accessed the bacterial community associated to leaves with and without anthracnose symptoms, combining culture-dependent and -independent methodologies and also investigated the biotechnology potential and biocontrol of culture-dependent bacteria. The bacterial community accessed by culture-dependent and -independent manner presented similarities, both presented higher bacterial richness but lower bacterial diversity in asymptomatic leaves when compared with symptomatic leaves, and both communities presented the Proteobacteria phylum as the most abundant one. Comparisons between the endophytic and epiphytic bacterial isolates associated with leaves with and without anthracnose symptoms showed that the onset of anthracnose disease on leaf seemed to be the most important factor that modified the bacterial community structure. Regarding the differences between symptomatic and asymptomatic tissue it was possible to identify some genera most frequently accessed in symptomatic plants such as Pseudomonas, Stenotrophomonas and Pantoea accessed in both culture-dependent and independent methodologies. However, the cultureindependent approach of bacterial accessed others abundants taxa that differed significantly between plants. Symptomatic leaves showed Acinetobacter, Acidobacter_GP1 and Sphingobacteria and asymptomatic leaves presented taxa Methylobacterium, Beijerinckia, group Bacilli and a group of unclassified Rhizobiales. In addition, endophytic and epiphytic isolates microorganisms were tested with the pathogen Colletotrichum sp. in antagonism assays, and isolates from the genus Bacillus, Stenotrophomonas, Pantoea, Erwinia, Entereobacter, Pseudomonas, and others, showed inhibition of growth of the fungus. The bacterial isolates were also tested for production of hydrolytic enzymes and siderophore. Many isolates showed protease and siderophore production. It was possible to correlate the production of amylase, lipase and poligalacturanase with isolates from symptomatic tissue.

Biochar is the solid, carbon-rich by-product obtained from pyrolysis. It offers the prospect of long-term carbon sequestration and soil conditioning with agronomic benefits, often referred to as the ‘biochar effect‘. These multiple direct or indirect changes in the soil plant interface have also been associated with the control of plant diseases by influencing the host’s systemic induced resistance. The biological impact of biochar on the phytopathology of a major cereal grain has not yet been investigated. The most damaging foliar disease of barley in the UK is Rhynchosporium leaf blotch caused by the hemibiotrophic fungal pathogen Rhynchosporium commune. The aim of this project was to evaluate biochar performance and effectiveness as a disease control agent in the barley – R. commune – pathosystem, and attempted to identify underlying mechanisms by which biochar may function in the interaction between barley and the causal pathogen. Therefore, a unique set of nine slow pyrolysis biochars were established along a 350 to 800°C pyrolysis temperature gradient, with eight of these made from pelleted softwoods and a single one made from Miscanthus straw. A comprehensive biochar quality assessment was undertaken and established that the biochars differed in their chemical composition, which largely depended on production parameters, predominantly temperature (P < 0.05). The analysis proposed that biochar 9, made from Miscanthus at 800°C, showed added value as a soil conditioner over softwood biochars, due to higher pH, mineral ash and macronutrient recoveries, which pointed towards a possible liming potential. Regardless of the feedstock, biochars pyrolysed above 600°C indicated potential use for carbon sequestration purposes, due to higher carbon stability. Short-term controlled bioassays showed significant restricted growth of R. commune mycelium on defined medium to direct (1.0% w/w) and indirect volatile exposure from certain biochars (P < 0.001). The findings suggested a synergistic effect of the softwood biochars acidic nature and presence of fungicidal compounds, with observed inhibition of 100% attributed to re-condensation of tarry vapours onto biochar surfaces during pyrolysis. Qualitative biochar volatile organic compound analysis was conducted and identified biocide active phenolic and organic acid compounds, similar to those commonly found in smoke, bio-oils or wood vinegars. These findings proposed possible application for mitigation of inoculum pressure in field-grown barley, but the toxic nature of volatiles raised concerns over risks to human and environmental health, as also evidenced by detrimental barley growth effects. Subsequent controlled in vivo and in planta experiments revealed significant (P < 0.05) symptomatic barley leaf blotch reduction effects of up to 100%, following 5% (w/w) application of biochars 4, 5, 8 and 9. Barley plants transcriptional changes in ISR-dependent LOX2 and SAR-dependent PR1-b expression in planta verified systemic induced resistance as mechanisms behind the significant disease suppression of barley plants grown in soil amended with biochar 5 and 8. Disease reduction and biochar mediated induced resistance was attributed to either low concentrations of phytotoxic compounds, a direct toxicity effect from fungicidal compounds or indirect promotion of beneficial microbes. The results provided evidence, that in the case of the studied pathosystem, there is potential for biochar with specific characteristics to be considered as a soil amendment, offering not only carbon sequestration, but also possible improved disease resistance.

Multi-services cover crops (MSCC) grown during fallow period between two cash crops provide various ecosystem services. Among species used as MSCC, crucifers can efficiently prevent nitrate and sulphate leaching by catching residual soil mineral nitrogen (N) and sulphur (S) afterthe preceding cash crop (N and S catch crop services). Crucifers also have a unique capacity to suppress pathogens due to the biocidal hydrolysis products of endogenous secondary metabolites called glucosinolates (GSL). The aim of our study was to assess the provision of various ecosystem services linked to N, S cycles and biocontrol potential for a wide range of bispecific crucifer-legume mixtures in comparison to sole cover crops of legume and crucifer. We carried out experiments in 2 contrasted sites (Toulouse and Orléans regions, France) during 2 years in order to assess these services and the compatibility of various bi-specific crucifer-legume mixtures. We tested a great diversity of species, such as i) crucifers : rape, white mustard, Indian mustard, Ethiopian mustard, turnip, turnip rape, radish and rocket, and ii) legumes: Egyptian clover, crimson clover, common vetch, purple vetch, hairy vetch, pea, soya bean, faba bean, and white lupin. Our study demonstrated that crucifer-legume mixtures can provide and mutualize various ecosystem services by reaching from 2 thirds (GSL production, S and N green manure) to the same level ofservice (N and S catch crop) than the best sole family of species. GSL profile and concentration did not change in mixtures meaning that crucifer-pests interactions were identical. Through a literature review we also illustrated that biocontrol services of crucifers could be largely maintained in crucifer-legume mixtures for a wide range of pathogens and weeds while reducing potential disservices on beneficials and increasing N related service

<p><i>Paenibacillus polymyxa</i> belongs to the group of plant growth promoting rhizobacteria (PGPR). Activities associated with <i>P. polymyxa</i>-treatment of plants in earlier experiments include, e.g., nitrogen fixation, soil phosphorus solubilization, production of antibiotics, auxin, chitinase, and hydrolytic enzymes, as well as promotion of increased soil porosity. My thesis work showed that, in stationary phase, <i>P. polymyxa</i> released the plant hormone cytokinin isopentenyladenine, in concentrations of about 1.5 nM.</p><p>In a gnotobiotic system with <i>Arabidopsis thaliana</i> as a model plant, it was shown that <i>P. polymyxa</i>-inoculation protects plants; challenge by either the pathogen <i>Erwinia carotovora</i> (biotic stress) or induction of drought (abiotic stress) showed that pre-inoculated plants were significantly more resistant than control plants. By RNA-differential display on RNA from <i>P. polymyxa</i>-treated or control plants, changes in gene expression were tested. One mRNA, encoding ERD15 (drought stress-responsive gene) showed a strong inoculation-dependent increase in abundance. In addition, several biotic stress-related genes were also activated by <i>P. polymyxa</i>. </p><p>Antagonism towards the fungal pathogens <i>Phytophthora palmivora</i> and <i>Pythium aphanidermatum</i> was studied. <i>P. polymyxa</i> counteracted the colonization of zoospores of both oomycetes on <i>A. thaliana</i> roots, and survival rates of plants treated with <i>P. polymyxa</i> were much higher when challenged by <i>P. aphanidermatum</i>. </p><p>Using a green fluorescent protein-tagged isolate of <i>P. polymyxa</i>, colonization of <i>A. thaliana</i> roots was investigated. Two main conclusions can be drawn. Firstly, the bacterium enters the root tissue (but not leaves) and is abundantly present in intercellular spaces. Secondly, the root becomes severely damaged, indicating that – under some conditions – <i>P. polymyxa</i> is a "deleterious bacterium", and in others it promotes growth. Based on work presented in my thesis, I argue that a balance between the activities of a PGPR, the genetic background and physiological state of a plant, and the environmental conditions employed in test systems, ultimately determines the resulting effect. </p>

Paenibacillus polymyxa belongs to the group of plant growth promoting rhizobacteria (PGPR). Activities associated with P. polymyxa-treatment of plants in earlier experiments include, e.g., nitrogen fixation, soil phosphorus solubilization, production of antibiotics, auxin, chitinase, and hydrolytic enzymes, as well as promotion of increased soil porosity. My thesis work showed that, in stationary phase, P. polymyxa released the plant hormone cytokinin isopentenyladenine, in concentrations of about 1.5 nM. In a gnotobiotic system with Arabidopsis thaliana as a model plant, it was shown that P. polymyxa-inoculation protects plants; challenge by either the pathogen Erwinia carotovora (biotic stress) or induction of drought (abiotic stress) showed that pre-inoculated plants were significantly more resistant than control plants. By RNA-differential display on RNA from P. polymyxa-treated or control plants, changes in gene expression were tested. One mRNA, encoding ERD15 (drought stress-responsive gene) showed a strong inoculation-dependent increase in abundance. In addition, several biotic stress-related genes were also activated by P. polymyxa. Antagonism towards the fungal pathogens Phytophthora palmivora and Pythium aphanidermatum was studied. P. polymyxa counteracted the colonization of zoospores of both oomycetes on A. thaliana roots, and survival rates of plants treated with P. polymyxa were much higher when challenged by P. aphanidermatum. Using a green fluorescent protein-tagged isolate of P. polymyxa, colonization of A. thaliana roots was investigated. Two main conclusions can be drawn. Firstly, the bacterium enters the root tissue (but not leaves) and is abundantly present in intercellular spaces. Secondly, the root becomes severely damaged, indicating that – under some conditions – P. polymyxa is a "deleterious bacterium", and in others it promotes growth. Based on work presented in my thesis, I argue that a balance between the activities of a PGPR, the genetic background and physiological state of a plant, and the environmental conditions employed in test systems, ultimately determines the resulting effect.

S'avaluaren 58 soques de Pseudomonas fluorescens i Pantoea agglomerans per la seva eficàcia en el biocontrol de la malaltia causada per l'oomicet Phytophthora cactorum en maduixera i pel nematode formador de gal·les Meloidogyne javanica en el portaempelt GF-677.Es desenvolupà un mètode ex vivo d'inoculació de fulla amb l'objectiu de seleccionar soques bacterianes com a agents de control biològic de P. cactorum en maduixera. Tres soques de P. fluorescens es seleccionaren com a soques eficaces en el biocontrol del patogen en fulles i en la reducció de la malaltia en plantes de maduixera. La combinació de soques semblà millorar la consistència del biocontrol en comparació amb les soques aplicades individualment.Tres soques de P. fluorescens es seleccionaren per la seva eficàcia en la reducció de la infecció de M. javanica en portaempelts GF-677. La combinació d'aquestes soques no incrementà l'eficàcia del biocontrol, però semblà reduir la seva variabilitat. / 58 Pseudomonas fluorescens and Pantoea agglomerans strains were evaluated for their biocontrol efficacy against the oomycete Phytophthora cactorum in strawberry and the root-knot nematode Meloidogyne javanica in GF-677 rootstocks.An ex vivo detached leaf inoculation method was developed to select bacterial strains as biological control agents of P. cactorum in strawberry. Three P. fluorescens strains were selected as effective in biocontrol of the pathogens on leaves and in disease reduction in strawberry plants. Combination of strains improved biocontrol consistency compared to strains applied individually. Three P. fluorescens strains were selected for their efficacy in M. javanica infection reduction in GF-677 rootstocks. Combination of these strains did not increase biocontrol efficacy, but reduced its variability.

Le aflatossine sono tra i composti naturali conosciuti più cancerogeni. Queste molecole, tossiche sia per gli animali sia per l’uomo, sono prodotte su importanti colture, quali mais, arachidi e cotone da differenti specie fungine di Aspergillus in particolare quelli afferenti alla sezione Flavi. In Italia il principale fungo responsabile della contaminazione da aflatossine su mais è A. flavus e l’area più esposta alla contaminazione è il nord della penisola dove si localizza circa il 90% della coltivazione del mais. Generalmente, le condizioni climatiche in questa area non sono favorevoli alla contaminazione da aflatossine; comunque stress idrico e alte temperature possono verificarsi durante il ciclo di crescita del mais favorendo la produzione di AFB1 da parte del fungo e determinando un accumulo superiore ai limiti di legge, come accadde nel 2003. Infatti, a partire dal 2003 più attenzione è stata dedicata alla caratterizzazione della popolazione italiana di A. flavus associate alla coltivazione del mais e allo sviluppo di una valida tecnica, come il controllo biologico degli isolati tossigeni mediante l’utilizzo di isolati non tossigeni, per ridurre la contaminazione da aflatossine. / Aflatoxins are the most carcinogenic natural compound known in nature. These molecules, toxic for animal and humans, are produced on important economic commodities worldwide by the secondary metabolism of several fungal species of Aspergilli of the section Flavi. In Italy the principal responsible of aflatoxins contamination on maize is A. flavus and the more exposed area to contamination is the northern of the peninsula where almost 90% of the cultivation is located. Generally, climatic conditions in this area are not favourable for aflatoxins contamination; however, reduced rainfall and increased temperature during maize developing season can occur along with associated levels of AFB1 exceeding the legal limits, as happened in 2003. Since this year, more attention has been dedicated to characterize Italian A. flavus populations associated with maize cultivation and to develop a useful tool to reduce aflatoxins contamination. To accomplish this goal, vegetative compatibility analysis, identification of atoxigenic isolates, evaluation of the ability of atoxigenic isolates to reduce in vitro aflatoxins produced by toxigenic isolates in vitro, selection of atoxigenic isolates potentially useful as biocontrol agents, individuate deletions in the aflatoxin biosynthesis gene cluster of selected atoxigenic isolates and biocontrol field trial with the selected potential biocontrol agents were achieved.