Although the pesticide DDT has been banned from use in Canada for more than three decades, DDT still persists in Canadian farmlands at detectable levels. Much effort, such as incineration, thermal desorption, and bioremediation, has been used to remediate DDT contaminated soils, but so far it is either too expensive or impractically slow. In this study, a three-year period of field trials was performed to investigate phytoremediation of DDT contaminated soil. In the field trials, millet, fall rye, sugar beet, potato, and pumpkin, treated with plant growth-promoting rhizobacteria (PGPR) were planted on two sites. As well, untreated plants were planted as a control. Plant growth, and 4,4’-DDT plus 4,4’-DDE concentrations in plant tissues and soil were monitored regularly. Comparing the plant growth between PGPR treated and untreated, PGPR significantly promoted the plant growth. On site 1, the root length and root weight of fall rye treated with PGPR were 16% and 44% greater, respectively, compared to the untreated plants. The root and shoot dry weights of millet treated with PGPR were 38% and 47% greater than those untreated plants. Root dry weight of sugar beet treated with PGPR was increased by 74% compared to untreated sugar beet. A significant effect of growth promotion was also observed in pumpkin and potato treated with PGPR. Following plant growth, DDT detection in plants was performed. 4,4’-DDT and 4,4’-DDE were found in plant tissues of fall rye, millet, sugar beet, and pumpkin. The concentrations of 4,4’-DDT and 4,4’-DDE in fall rye roots were 0.61 and 0.59 μg/g, respectively. In pumpkin tissues at harvest, 4,4’-DDT and 4,4’-DDE concentrations were 0.67 and 1.64 μg/g in roots, 1.06 and 2.05 μg/g in the lower stems, and 0.2 and 0.32 μg/g in the upper stems. The data indicated that it is feasible to phytoremediate DDT from contaminated soil. In addition, 4,4’-DDT concentrations in soils with different plant species were determined. In millet plot on site 1, 4,4’-DDT concentration in rhizosphere soil dropped by 41% in 2006 compared to 4,4’-DDT concentration at t0. In sugar beet plot on site 1, 28% of 4,4’-DDT dropped in rhizosphere soil in 2007. In pumpkin plot on site 1, 4,4’-DDT in rhizosphere soil was decreased by 22% in 2007. The results show that 4,4’-DDT concentration in rhizosphere soil was significantly lower than the initial level of DDT. Based on the data of 4,4’-DDT in soils and plant tissues, a mass balance was constructed and calculated. The preliminary mass balance shows that the total amount that DDT decreased in rhizopshere soil approximately equals to the total amount of DDT accumulated in plant tissues. This indicates that phytoextraction is the mechanism of DDT phytoremediation. In addition, PGPR promoted plant growth and then enhanced the phytoremediation efficiency of DDT. Therefore, the research indicates that PGPR assisted phytoremediation has a great potential for remediation of DDT and other chlorinated aromatics from impacted soil.

Soil salinity affects an estimated one billion hectares worldwide. Excess salinity inhibits plant growth, limiting crop production. This is caused by osmotic stress in saline soil, nutrient imbalance and specific ion toxicity. There have been many methods of remediation investigated, including excavation, soil washing and phytoremediation. Phytoremediation involves the growth of plants on impacted soils to degrade or sequester contaminants. The remediation of salts relies on the uptake of ions into plant biomass where the salt is sequestered and the biomass can then be harvested. This method removes the salt from the site and leaves the top soil in place, which aids in revegetation after site remediation is completed. Plant-growth promoting rhizobacteria (PGPR) improves plant growth by lowering the levels of stress ethylene within the plant, thereby increasing the biomass available to sequester ions. The objectives of this research were to investigate the efficiency of phytoremediation of salt impacted soils in field remediation sites. Previously isolated strains of PGPR (UW3, Pseudomonas putida; UW4, Pseudomonas putida; and CMH3, Pseudomonas corrugata) were used in field trials involving the planting of oats (Avena sativa), annual ryegrass (Lolium multiflorum), tall wheatgrass (Agropyron elongatum) and tall fescue (Festuca arundinacea C.V. Inferno). The salt tolerance of various switchgrass (Panicum virgatum L.) cultivars (Cave-In-Rock, Southlow, Forestburg, and common) was compared to tall wheatgrass and Inferno tall fescue to investigate the potential of switchgrass for phytoremediation. Improvement of seed germination under salt stress by H2O2 pre-treatment was investigated both as an individual treatment and in combination with CMH3 treatment. The ion uptake into plant biomass was iii compared to the change in salinity, to determine how much of the decrease in site salinity is accounted for by uptake of salt by plants. H2O2 pretreatment resulted in a 50% increase in root and shoot emergence of tall wheatgrass under 75 mM NaCl stress compared to control treatments, which matched the germination improvement observed with PGPR treatment. The combination of H2O2 and CMH3 showed a similar improvement to root emergence under stress, but had no observable effect on shoot emergence when compared to the no-H2O2-no-PGPR control. Switchgrass cultivars showed a lower germination rate than tall wheatgrass at salt levels from 0 mM to 150 mM NaCl. The measured uptake of Na+, K+, Ca2+, Mg2+ and Cl- into plant biomass during a phytoremediation field trial was able to account for approximately 70% of the observed change in salinity in 2008. In 2009 the uptake of Na+ and Cl- into Kochia scoparia, a weed species that invaded the field site after a hard frost, was able to account for 36% of the observed change in salinity.

Soil salinity affects an estimated one billion hectares worldwide. Excess salinity inhibits plant growth, limiting crop production. This is caused by osmotic stress in saline soil, nutrient imbalance and specific ion toxicity. There have been many methods of remediation investigated, including excavation, soil washing and phytoremediation. Phytoremediation involves the growth of plants on impacted soils to degrade or sequester contaminants. The remediation of salts relies on the uptake of ions into plant biomass where the salt is sequestered and the biomass can then be harvested. This method removes the salt from the site and leaves the top soil in place, which aids in revegetation after site remediation is completed. Plant-growth promoting rhizobacteria (PGPR) improves plant growth by lowering the levels of stress ethylene within the plant, thereby increasing the biomass available to sequester ions. The objectives of this research were to investigate the efficiency of phytoremediation of salt impacted soils in field remediation sites. Previously isolated strains of PGPR (UW3, Pseudomonas putida; UW4, Pseudomonas putida; and CMH3, Pseudomonas corrugata) were used in field trials involving the planting of oats (Avena sativa), annual ryegrass (Lolium multiflorum), tall wheatgrass (Agropyron elongatum) and tall fescue (Festuca arundinacea C.V. Inferno). The salt tolerance of various switchgrass (Panicum virgatum L.) cultivars (Cave-In-Rock, Southlow, Forestburg, and common) was compared to tall wheatgrass and Inferno tall fescue to investigate the potential of switchgrass for phytoremediation. Improvement of seed germination under salt stress by H2O2 pre-treatment was investigated both as an individual treatment and in combination with CMH3 treatment. The ion uptake into plant biomass was iii compared to the change in salinity, to determine how much of the decrease in site salinity is accounted for by uptake of salt by plants. H2O2 pretreatment resulted in a 50% increase in root and shoot emergence of tall wheatgrass under 75 mM NaCl stress compared to control treatments, which matched the germination improvement observed with PGPR treatment. The combination of H2O2 and CMH3 showed a similar improvement to root emergence under stress, but had no observable effect on shoot emergence when compared to the no-H2O2-no-PGPR control. Switchgrass cultivars showed a lower germination rate than tall wheatgrass at salt levels from 0 mM to 150 mM NaCl. The measured uptake of Na+, K+, Ca2+, Mg2+ and Cl- into plant biomass during a phytoremediation field trial was able to account for approximately 70% of the observed change in salinity in 2008. In 2009 the uptake of Na+ and Cl- into Kochia scoparia, a weed species that invaded the field site after a hard frost, was able to account for 36% of the observed change in salinity.

Soybean has a strong demand for nitrogen that can be acquired from atmosphere for vegetative growth and seed production through the symbiosis with the soil bacterium Bradyrhizobium japonicum (B. japonicum). However, the native soil bradyrhizobia may be ineffective in nitrogen fixation and the greatest limiting factor in increasing symbiotic nitrogen fixation is the inability to influence the infection of soybean roots by a desired strain of B. japonicum due to competition from the native bradyrhizobia. Previous studies have demonstrated the efficacy of a co-inoculum seed treatment on the symbiotic competency of the soybean cultivar LS90-1920 in greenhouse and field trials. The co-inoculation by the soil bacterium Streptomyces kanamyceticus (S. kanamyceticus) strain ATCC 12853 and strains of B. japonicum more efficient in nitrogen fixation and resistant to the antibiotics kanamycin and neomycin may have an advantage over the native bradyrhizobia regarding soybean root infection (Gregor et al., 2003). However, inconsistent inoculation responses in field trials and low efficacy in nodule competency by selected Bradyrhizobium japonicum (B. japonicum) co-inocula were observed under greenhouse conditions. These results were attributed to insufficient population size or growth of viable co-inocula associated with the seed treatments. This recent study showed that the nodulation response of LS90-1920 to B. japonicum strains KNI-1 and KNI-3 is independent of the inoculum dose and age of the broth culture. Iron supplement to the inoculum nutrient solution significantly increased the total biomass of nodules formed by strain KNI-1 but not by strain KNI-3 on a per plant basis and had no effect on the nodule number regardless of B. japonicum strain. In the glass bead viability study, the effect of inoculum nutrient solution concentration on the viability of bacterial co-inocula is species-specific and influenced by seed coating material. The growth of Pseudomonas putida strains displayed a dependency on the concentration of the inoculum nutrient solution with graphite or vermicompost as the seed coating material treatment or with activated charcoal treatment associated with 0.1% or 1.0 % inoculum nutrient solution. The seed coating material treatments of vermicompost and graphite promote stronger growth of S. kanamyceticus strain ATCC 12853 than the activated charcoal treatment. After a six-day incubation at 28oC, a 1.0 % inoculum nutrient solution maintained the highest viable populations of co-inocula with activated charcoal and a 0.1% inoculum nutrient solution was most effective in the maintenance of the co-inocula population when graphite or vermicompost was employed as the seed coating material. By applying the appropriate level of inoculum nutrient solution, the viability of a selected B. japonicum KNI strain and co-inocula remained stable for six days in activated charcoal and graphite treatment regardless of the number of applied co-inocula. However, the vermicompost treatment did not maintain the viable populations of the B. japonicum KNI strains and P. putida strain G11-32 but support the vigorous growth of S. kanamyceticus strain ATCC 12853 and P. putida strain 17-29. Greenhouse studies employing sterilized vermiculite as a soybean growth medium showed no significant differences in nodule competency by the inoculum/seed coating treatments associated with B. japonicum strain KNI-1. However, the co-inoculum treatments significantly increased either the total nitrogenase activity (B. japonicum strain KNI-3 with S. kanamyceticus strain ATCC 12853) or the nodule number (B. japonicum strain KNI-3 with S. kanamyceticus strain ATCC 12853 and P. putida strain 17-29) versus the singular inoculum treatment of strain KNI-3. Soil-pot studies under the same greenhouse conditions showed no significant differences in the nodule competency between the inoculum treatment of B. japonicum strain KNI-3, the co-inoculum treatment of strain KNI-3 and S. kanamyceticus, and the non-inoculated control regardless of seed coating material. However, co-inoculation of emergence-promoting rhizobacteria (Pseudomonas putida strain 17-29 and G11-32) with strain KNI-3 and S. kanamyceticus strain ATCC 12853 may improve the total nitrogenase activity and specific nitrogenase activity, depending on the seed coating material and soil type. The treatment with activated charcoal employed as a seed coating material and the co-inocula of strain KNI-3, S. kanamyceticus strain ATCC 12853 and P. putida strains 17-29 or G11-32 showed significantly higher total nitrogenase activity (Stoy silt loam) and specific nitrogenase activity (Drummer silty clay loam) versus the non-inoculated control. For the Bethalto silty clay loam, the same co-inoculum treatment associated with graphite and vermicompost as the seed coating material significantly increased the total nitrogenase activity. The seed coating treatment by activated charcoal enhanced nodulation competency for both the 2010 and 2011 field trials resulting in higher grain yield, seed nitrogen content, and seed protein content versus the seed coating treatment by graphite. No significant differences by the inoculum treatments were determined.

Biofertilizer (or microbial soil inoculants) may be used to reduce current fertilizer inputs (organic or conventional methods), while maintaining or improving crop plant growth and yield. Pseudomonas putida is a plant-growth promoting rhizobacterium (PGPR) that solubilizes inorganic phosphorous or mineralizes organic phosphates, produces siderophores (enhancing Fe availability for plants, reducing Fe access to pathogenic fungi), and is known to improve plant growth by assisting with nutrient availability, synthesis of plant hormones (indole acetic acid regulation production and/or degradation, or ethylene regulation through aminocyclopropane carboxylate deaminase activity), and acts as a biological control of several plant pathogens and pests (Rhizoctonia solani, Bemisia tabaci). Recommendations for inoculum population density, application timing, and species of PGPR, vary mainly based on geographic and weather conditions, and their relationship to each horticultural crop, which needs to be better understood. Two studies were conducted in 2014 and 2015 at the Southern Illinois Horticulture Research Center to determine the optimum application timing and dosage of Pseudomonas putida strains 17-29 and G11-32 to improve plant growth and yield on two important horticultural crops: field grown ‘Revolution’ bell peppers and greenhouse grown ‘Rocky Top’ determinate tomatoes. Field pepper results indicated that the inoculum population density increased early-season vigor, plant height and stem caliper (P < 0.05), as well as late-season plant vigor, height (cm), leaf chlorophyll index (SPAD), and stem caliper (mm) (P < 0.05) for inoculum population density. Although early harvests (first two harvests) fruit yield increased with rhizobacteria inoculum population density (P < 0.05) for total fruit weight (2014, 2015) and number (2014), late-season fruit yields (last three harvests) were not affected. Combined fruit yield total weight (all five harvests) also increased (P < 0.05) by inoculum population density in the order: 10^0 < 10^3 < 10^5 < 10^7 < 10^9. It appears that higher early-season and combined harvest yields were higher resulting from increasing inoculum population densities were greater due to increased early season growth from the bacterial treatments during plug growth phase. Tomato results indicated that inoculum population density increased early growth and late growth vigor, height (cm), leaf chlorophyll index (SPAD), leaf number, flower number, fresh leaf weight (g), fresh stem weight, and dry leaf weight (P < 0.05). Tomato growth was effected by inoculum population density treatment however, yields differences were not observed.

Iron is abundant in most agricultural systems, however it is also one of the three most limiting nutrients for crop growth. This can be attributed to iron’s low solubility in aerobic and alkaline conditions, rendering it non-bioavailable for plant uptake. With around 1/3 of the world arable land presenting conditions that limit iron solubility, deciphering the plant machinery behind iron uptake and identifying microbial benefits to iron deficiency are of major interest. In this work, 33 endophytic bacterial isolates previously isolated from three regions in Jordan were tested for iron stress alleviation of Arabidopsis plants with the goal of identifying novel interaction mechanisms. On media with a low concentration of bioavailable iron, 11 isolates were found to be beneficial, while 15 isolates behaved in a pathogenic manner, reducing plant growth in both control as well as limited iron conditions. Beneficial isolates were then tested in plant assays with non-bioavailable iron, we concluded that our strains are also beneficial in these conditions. To further characterize the interaction between the beneficial strains and Arabidopsis plants, gene expression was assessed for plants colonized with select strains. The highest expression of iron-deficiency response genes was at day 6. The increase in expression was also met with an increase in colonization of plants at day 6. Mutant studies revealed that the beneficial effect by the bacterial isolates is dependent on the coumarin pathway, with mutants in FERULOYL-COA 6-HYDROXYLASE 1, f6’h1, showing a drastic decrease in fresh weight compared to wild type counterparts. We also discovered the phytohormone abscisic acid as an important contributor to iron stress alleviation by the beneficial isolates. Colonization assays as well as additional mutant studies will be necessary to further assess the effect of f6’h1 mutants on plant-microbe interaction as well as ABA’s role in plants under iron deficient conditions.

Submitted by Angela Maria de Oliveira (amolivei@uepg.br) on 2018-07-24T16:47:17Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Silvia Ap F Albuquerque.pdf: 2057064 bytes, checksum: ca90a9ed638cc415e9baf99ff0b848ab (MD5) / Made available in DSpace on 2018-07-24T16:47:17Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Silvia Ap F Albuquerque.pdf: 2057064 bytes, checksum: ca90a9ed638cc415e9baf99ff0b848ab (MD5) Previous issue date: 2016-02-25 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Rizobactérias promotoras do crescimento vegetal (PGPR) estimulam o desenvolvimento das plantas hospedeiras, e a planta, por sua vez, em conjunto com as condições de cultivo, têm um significativo efeito sobre a estrutura da comunidade bacteriana da rizosfera. Nesse estudo, foi analisada a diversidade de rizobactérias isoladas de milho inoculado com diferentes biofertilizantes e cultivado na presença de diferentes doses de nitrogênio. Além disso, foi avaliado o perfil dos isolados por espectrometria de massa e o potencial de tais isolados na produção de sideróforos, protease, compostos indólicos, cianeto e celulase e na solubilização de fosfato; atividades relacionadas à promoção do crescimento vegetal. Os setenta e sete isolados bacterianos obtidos a partir do uso de cinco diferentes meios de cultivo (JMV, JNFb, NFb, LGI e LGI-P) livres de amônia, foram identificados pelo sequênciamento parcial do gene 16S rRNA. O biofertilizante e as dosagens de nitrogênio não interferiram significativamente na composição da comunidade de bactérias diazotróficas isoladas da rizosfera de milho. O meio JNFb permitiu o isolamento de um número maior de indivíduos, e esses apresentaram maior riqueza e diversidade. Dentre os isolados, houve a predominância das classes β e γProteobacteria, sendo Burkholderia o gênero mais abundante. A análise por espectrometria de massa mostrou potencial para separar gêneros bem representados em nível de estirpe. Mais da metade dos isolados produziram sideróforos (58%) e protease (50,7%); solubilização de fosfatos (36,2%) e aproximadamente um quarto deles (23,1%) foram capaz de produzir celulase. A produção de cianeto de hidrogênio se mostrou bastante rara, sendo detectada em apenas 4,3% dos isolados, todos pertencentes ao gênero Pseudomonas sp. Todas as bactérias analisadas apresentaram ao menos uma atividade e 55% apresentam três ou mais. Análises de componentes principais indicaram que (1) os gêneros Burkholderia sp. e Luteibacter sp., tem correlação significativa (p <0,05 ou p<0,001) com a produção de protease, sideróforos e solubilização de fosfato, (2) Bacillus sp. e Luteibacter sp., com produção de compostos indólicos e celulase e (3) Pseudomonas sp., com produção de protease, cianeto e sideróforos, compostos indólicos e celulase. Diante da demanda de biofertilizantes de gramíneas capazes de substituir parcialmente ou integralmente o uso de fertilizantes químicos, os isolados que apresentaram diversas atividades promotoras do crescimento vegetal se mostram promissores para aplicação como biofertilizante. / Plant growth promoting rhizobacteria (PGPR) stimulate the development of their host plant, and the plant, in turn, together with the culture conditions has a significant effect on rhizospheric bacterial community structure. In this study, the diversity of cultivable bacteria associated with the rizosphere of maize inoculated with different biofertilizers and growth in different nitrogen doses was analyzed. It was also evaluated the mass spectrometry profile of the isolates and their potential to produce siderophores, protease, indole compounds, cyanide and cellulose, and to solubilize phosphate, all activities related to plant growth promotion. The seventy seven bacterial isolates obtained by the use of five different nitrogen-free media (JMV, JNFb, NFb, LGI e LGI-P) were identified by partial sequencing of the 16S rRNA gene. The biofertilizers and the nitrogen doses did not interfere in the composition of the isolated diazotrophs from maize rhizosphere. JNFb medium permitted the isolation of a greater number of individuals, and they presented the highest richness and diversity. Among the isolates, there was a predominance of β e γ-Proteobacteria classes, being Burkholderia the most abundant genus. Mass spectrometry analysis showed potential to separate well represented genus into strain, evidencing new species of the Burkholderia genus. More than half of the isolates produced siderophores (58%) and protease (50.7%); solubilize phosphate (36.2%) and approximately a quarter of them (23.1%) were able to produce cellulase. The hydrogen cyanide production showed to be rare, being detected in only 4.3% of isolates, all belonging to the genus Pseudomonas sp.. All analyzed bacteria showed at least one activity and 55% showed three or more. Principal component analysis indicated that (1) Burkholderia sp. e Luteibacter sp. genus have significant correlation (p <0,05 or p<0,001) with protease and siderophores production and phosphate solubilization, (2) Bacillus sp. and Luteibacter sp. have significant correlation with indole compounds and cellulase production and (3) Pseudomonas sp. has significant correlation with protease, cyanide, siderophores, indole compounds and cellulase production. Based on the demand for grass biofertilizers able to partially or completely replace chemical fertilizers, the isolates which have several activities that promote plant growth are promising to be used as biofertilizer. Some genus clearly they share at least three equal activities featuring redundant function among them.

Depuis 1960, la grande majorité des variétés de blé sont des variétés naines, présentant de nombreuses différences par rapport aux variétés plus anciennes. Elles sont capables de mieux utiliser les apports d’engrais synthétiques et présentent des rendements supérieurs. Cependant, peu d’intérêt a été porté au système racinaire et aux impacts sur les interactions avec les bactéries du sol. Pourtant, la main de l’Homme pourrait avoir rendu caduque les effets bénéfiques apportés par les PGPR (Plant Growth-Promoting Rhizobacteria) aux plantes, et les traits génétiques permettant les interactions entre plante et PGPR pourraient ne pas avoir été sélectionnés chez les génotypes de variétés modernes. L’hypothèse dans cette thèse est que les PGPR intéragiraient mieux avec des variétés anciennes qu’avec des variétés modernes. Nous avions à disposition 199 accessions de blé tendre représentatif des variétés de blés sélectionnées depuis le milieu du 19ème siècle. Par une approche de criblage, nous avons évalué in vitro la capacité de deux PGPR, Pseudomonas kilonensis F113 et Azospirillum brasilense Sp245, à coloniser les racines de ces génotypes de blé, et a y exprimer des gènes impliqués dans des fonctions bénéfiques pour la croissance de la plante. Par la suite nous avons testé si les résultats obtenus in vitro se traduisaient en une amélioration de la croissance du blé par une approche d’inoculation réalisée en sol. Enfin, une étude aux champs a été menée pour analyser l’impact des génotypes de blé sur les bactéries indigènes du sol. Ces travaux ont montré (1) une meilleure aptitude de F113 et Sp245 à interagir avec les génotypes anciens in vitro, (2) de meilleurs effets phytostimulateurs suite à l’inoculation de PGPR chez les génotypes de blés ayant présenté de bons résultats lors du criblage et (3) un impact du génotype de blé sur les bactéries indigènes associées à ses racines, notamment entre génotypes anciens et génotypes modernes / Since 1960, the great majority of wheat modern varieties are dwarf varieties (because of Rht genes), showing multiple differences compared to ancient varieties. Thus, they are more able to use synthetic fertilizers used in huge quantities since the mid-20th and show higher yield. However, few studies have been made regarding the impact of modern breeding on root systems and on interactions of crops with soil bacteria. Yet, these evolutions in agricultural practises could have reduced the beneficial effects brought by PGPR (Plant Growth-Promoting Rhizobacteria), and the genetic traits involved in these interactions between plant and PGPR may have not been selected in modern genotypes. Our work hypothesis in this thesis is that PGPR are more able to interact with ancient genotypes than modern ones. To test this hypothesis, we had 199 bread wheat accessions representative of the wheat varieties selected since the mid-19th. Using an in vitro screening approach, we assessed the abilities of two PGPR model strains, Pseudomonas kilonensis F113 and Azospirillum brasilense Sp245, to colonize the roots of these genotypes and to express genes involved in plant-beneficial functions. Then, we assessed whether the results obtained in vitro had a biological significance by measuring the amelioration of growth performance of wheat genotypes using a soil pot inoculation experiment under greenhouse. Finally, an in-field study was performed to analyse the impact of wheat genotypes on the indigenous bacterial communities. This work showed (1) a better ability of F113 and Sp245 to interact with ancient wheat genotypes than modern ones, (2) better growth performance improvements in wheat genotypes that showed good results during screening experiments and (3) an impact of wheat genotypes on indigenous bacterial communities, notably between ancient and modern genotypes

Com a crescente preocupação por práticas agrícolas mais sustentáveis, o uso de rizobactérias promotoras de crescimento de plantas (PGPR) tem recebido cada vez mais atenção por sua capacidade em melhorar a performance das plantas assim como aumentar sua resistência contra insetos e patógenos. Neste trabalho foi demonstrado que a inoculação de plantas de trigo com a rizobacteria Azospirillum brasilense reduziu alguns sintomas característicos de plantas infectadas pelo vírus do nanismo amarelo da cevada (BYDV), bem como a população do afídeo vetor, Rhopalosiphum padi, nessas plantas. A redução de alguns sintomas relacionados a doença foi associada à resistência sistêmica induzida, desencadeada pelo aumento nos níveis de ácido jasmônico, fitohormônio amplamente conhecido na indução de resistência por bactérias benéficas contra patógenos. Entretanto, não foi possível elucidar as vias de defesa que auxiliaram na diminuição da população do vetor. Adicionalmente, verificou- se que a inoculação bacteriana alterou os padrões de preferência hospedeira por ápteros não- virulíferos e virulíferos e alados de R. padi. Os dados apresentados nessa tese sugerem o grande potencial que a inoculação com A. brasilense pode ter no manejo do BYDV, influenciando não apenas o vírus, mas todo seu patossistema, uma vez que o crescimento populacional e o comportamento de seu vetor, R. padi, foram afetados pela interação BYDV-trigo-PGPR. / With the increasing concern for agricultural practices more sustainable, the use of plant growth promoting rhizobacteria (PGPR) has been received increasing attention for its ability to improve plant performance and increase plant resistance against insects and pathogens. In this work, it was demonstrated that the inoculation of wheat plants with the rhizobacteria Azospirillum brasilense, reduced some characteristic symptoms of plants infected by the barley yellow dwarf virus (BYDV), as well as the performance of its aphid vector, Rhopalosiphum padi. The reduction in disease severity was related to induced systemic resistance, triggered by the increase in the levels of jasmonic acid, phytohormone widely known to induce resistance by beneficial bacteria against pathogens. However, it was not possible to elucidate the pathways of defense involved in decrease the vector population. In addition, bacterial inoculation was found to affect the host preference of R. padi aptera non-viruliferous and viruliferous and alates. The data presented here suggest the great potential that the inoculation with A. brasilense can be in the management of BYDV, influencing not only the virus but all its pathosystem, considering that the population growth and the behaviour of its vector, R. padi, were affected by BYDV-wheat-PGPR interaction.