Il y a désormais un consensus autour de l’idée que nous devons réduire l’usage des pesticides (Plan Ecophyto). Il est donc nécessaire de développer des systèmes de cultures réduisants l’utilisation des pesticides au profit d’un système de production dans lequel on stimule les mécanismes de défense «naturels» des plantes. Dans ce contexte, on voit aujourd’hui se développer de nombreuses solutions d’origines chimique ou biologique à base de stimulateurs de défenses des plantes (SDP) mais dont l’efficacité est souvent jugée aléatoire. Dans ce travail, notre choix a porté sur l’utilisation des rayonnements UV-C pour stimuler les défenses de la laitue et de la tomate contre Botrytis cinerea. L’idée d’exploiter les rayonnements UV-C, comme stimulateurs des défenses des plantes à intérêt alimentaire en culture, n’a jamais été testée. Nos résultats démontrent clairement un effet stimulateur des défenses des plantes par des doses faibles et répétées d’UV-C (inférieur à 1,70 kJ/m2). Cette stimulation est associée au renforcement de la paroi cellulaire, à l’augmentation des composés phénoliques et à l’augmentation de l’activité de certaines enzymes antioxydantes. Lorsque le traitement par les rayonnements UV-C est combiné à l’agent biologique Bacillus subtilis aucun effet synergique ou même additif n’a été observé par rapport à un traitement simple UV-C ou B. subtillis. / There is now a consensus around the idea that we must reduce theuse of pesticides (Plan Ecophyto). It is therefore necessary to develop cropsystems that have less need to be protected by pesticides in favor of aproduction system in which the "natural" defense mechanisms arestimulated. In this context, many solutions of chemical or biological originbased on stimulation of plant defense are now being developed but theireffectiveness is often judged to be random. In this work, we chose to useUV-C radiation to stimulate the defenses of lettuce and tomato againstBotrytis cinerea. The idea of exploiting radiation UV-C, as a stimulant ofplant food-borne defenses in culture, has never been tested. Our resultsclearly demonstrate a stimulatory effect of plant defenses by low andrepeated doses of UV-C (less than 1.70 kJ/m2). This stimulation isassociated with a reinforcement of the cell wall, an increase in the phenoliccompounds and the activity of certain antioxidant enzymes. When treatmentwith UV-C radiation is combined with a biological agent Bacillus subtilis, nosynergistic or even additive effect has been observed compared with asimple UV-C or B. subtillis treatment. / Se ha establecido en el mundo entero la importancia sobre el controlde uno de los principales organismos fitopatológicos como lo es Botrytiscinérea, el cual demanda en la actualidad a los productores aplicarcontroles cónsonos con la protección del medio ambiente. Por consiguiente,se evaluó el uso de diferentes dosis de luz ultravioleta sola o encombinación con un agente de biocontrol (Basillus subtilis), con la finalidadde estimular las defensas naturales de dos especies vegetales (lechuga ytomate). Al respecto, los resultados establecieron que dosis menores de1,70 kJ/m2 de UV-C logran disminuir la sensibilidad de las plantas, sinafectar significativamente el desenvolvimiento del aparato fotosintético deambas especies. Así como, se observó un efecto antagónico del biocontrolsobre la UV-C cuando se combinan.

Plants have evolved multiple surveillance mechanisms to detect the presence of disease-causing organisms. One mode of surveillance is based on dozens of constitutively expressed resistance (R) genes. R genes recognize pathogen gene products as signals of invasion. We are interested in how plants evolve R genes to keep pace with rapidly evolving pathogen populations. The mechanisms that drive the evolution of new R genes are poorly understood. There is data that supports the relevance of recombination in the evolution of resistance gene clusters in plants. However, a more comprehensive understanding of the molecular biology of recombination and the impact recombination has on R gene evolution is necessary. The objectives of this dissertation were to develop a genetic screen that models meiotic unequal crossing over at a synthetic RPP8 (synthRPP8) resistance gene cluster and to assess the effect of abiotic stress on recombination with the synthetic RBCSB gene cluster (synthRBCSB) in Arabidopsis. The genetic screen utilized in these studies specifically identifies a novel recombinant gene and a concomitant gene duplication that results from meiotic unequal crossing-over by coupling chimeric gene formation to the activation of the firefly luciferase gene. Two synthRPP8 clusters were constructed and extensive optimization of screening conditions were performed. An initial screen of ~1 million synthRPP8 transgenic plants was performed and plants that expressed the luc+ phenotype were isolated and analyzed. Unexpectedly, background bioluminescence was found to interfere with the identification of bona fide luc+ synthRPP8 recombinants. An abiotic stress response assay was performed and the data suggests activation of a putative stress response element in the promoter of RPP8 is responsible for background levels of in vivo luciferase activity. The background bioluminescence could not be sufficiently reduced. Therefore, two additional synthRPP8 constructs, synthRPP8-3 and synthRPP8-4, were constructed and are currently being examined for their utility to model meiotic unequal crossing-over. UV-C treatment was shown to stimulate somatic unequal crossing over, as well as upregulate defense/stress response genes and transcription factors. Meiotic recombination may also be affected by stress. Therefore, the effect of UV-C irradiation on the frequency of unequal meiotic recombination between paralogous RBCSB genes and on the expression of genes associated with the defense/stress response was examined. We observed a ~2-fold increase in the frequency of meiotic recombination after UV-C irradiation but this increase was not statistically significant. We did not detect a significant alteration in the steady-state MYB10, PR-1 and HSF-3 mRNA levels by semi-quantitative RT-PCR. The expression data we gathered provided minimal support for whether the UV-C treatment was an effective DNA damaging agent. / Ph. D.

La contamination des vins par des microorganismes non désirés peut entraîner une dégradation importante du produit. Pour lutter contre ces problèmes, le dioxyde de souffre (SO2) est l’additif le plus utilisé actuellement pour ses propriétés antiseptiques et antioxydantes. Cependant, la limitation des intrants chimiques dans les vins est une des préoccupations majeures des consommateurs et producteurs. Les procédés de stabilisation physiques existants (flash pasteurisation, filtration tangentielle) présentent quant à eux des inconvénients, tels que leur cout énergétique ou leur maintenance complexe. Deux procédés innovants permettant d’assurer la stabilisation microbiologique des vins en alternative aux procédés classiques sont étudiés : le rayonnement ultraviolet (UV-C) et le chauffage ohmique. Les rayonnements UV-C (100 à 280 nm) sont connus pour leur effet germicide et déjà appliqués dans le traitement de l’eau et des surfaces. Cependant les liquides absorbants, tels que le vin, limitent fortement la profondeur de pénétration du rayonnement et donc l’efficacité du procédé. Un réacteur UV-C hélicoïdal a été développé, basé sur les propriétés hydrodynamiques des vortex de Dean, pour améliorer l’efficacité et l’homogénéité du traitement. Les performances de stabilisation ont été validées pour la première fois en alternative au mutage par SO2 de mouts liquoreux et avant la mise en bouteille de vins finis. De plus, les analyses chimiques et sensorielles menées sur les vins traités ne montrent aucun impact sur la qualité des vins. Le chauffage ohmique est ici utilisé comme procédé de stabilisation thermique des mouts et des vins. Lors du passage d’un courant à travers un matériau ayant une résistance électrique, l’énergie électrique est transformée en énergie thermique. La chaleur est alors générée à l’intérieur même de la matière à traiter. Les résultats des travaux ont montré pour la première fois que la rapidité et l’homogénéité de chauffe permettent une stabilisation efficace des vins et des mouts sans préjudices sur leur qualité. / Contamination of wines by undesired microorganisms may lead to significant deterioration of the final product. To combat these problems, sulfur dioxide (SO2) is the most widely used additive for its antiseptic and antioxidant properties. However, the limitation of chemical inputs in wines is one of the major concerns of consumers and producers. Existing physical stabilization processes (flash pasteurization, tangential filtration) have disadvantages, such as their energy cost or their complex maintenance. Two innovative processes to ensure the microbiological stabilization of wines as an alternative to conventional processes are studied: ultraviolet radiation (UV-C) and ohmic heating. UV-C radiation (100 to 280 nm) is known for its germicidal effect and already applied in the treatment of water and surfaces. However, absorbent liquids, such as wine, strongly limit the penetration depth of the radiation and hence the efficiency of the process. A helical UV-C reactor was developed, based on the hydrodynamic properties of Dean vortices, to improve the efficiency and homogeneity of the treatment. The stabilization performance was validated for the first time as an alternative to the SO2 mutage of sweet wines and before the bottling of finished wines. Moreover, the chemical and sensory analyzes carried out on the treated wines showed no impact on the quality of wines. Ohmic heating is used in this study as a method of thermal stabilization of musts and wines. During the passage of a current through a material having an electrical resistance, the electrical energy is transformed into thermal energy. The heat is then generated inside the material to be treated. The results of this work showed for the first time that heating rate and homogeneity of ohmic heating allow an effective stabilization of musts and wines without affecting their quality.

Made available in DSpace on 2014-06-12T18:02:39Z (GMT). No. of bitstreams: 2 arquivo166_1.pdf: 3384233 bytes, checksum: c4aa78c71c1e17f59c51cfcfd5e7a869 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2008 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O lançamento no meio ambiente de esgotos sanitários, em estados brutos ou parcialmente tratados, tem constituído uma ameaça à população. A irradiação por luz UV-C é uma técnica de ponta para desinfecção de águas de consumo e residuárias. A bactéria Pseudomonas aeruginosa é resistente ao tratamento convencional por cloração, devido à sua fisiologia oposta via de regra por uma cápsula extracelular, sendo responsável por infecções hospitalares em pacientes imunodeprimidos. Este trabalho está relacionado com o estudo da cinética do processo de desinfecção de água contaminada com a bactéria Pseudomonas aeruginosa por meio de Radiação UV-C. Os estudos cinéticos foram realizados em um fotorreator anular operando em batelada dentro de um ciclo contínuo. A fonte de radiação UV-C utilizada foi a lâmpada germicida, marca Philips modelo TUV 36W. Dois tipos de água modelo foram utilizados: a) água-modelo sem nutriente: suspensão de bactéria em água destilada previamente esterilizada, para processo com e sem radiação, b) água-modelo com nutriente: suspensão de bactéria em água destilada previamente esterilizada e meio asparagina, fazendo-se o estudo com radiação. A concentração de Pseudomonas aeruginosa foi quantificada por meio da técnica de contagem em placas. Concentração inicial da bactéria na água-modelo variou na faixa de 200 a 1600 UFC/cm3. Os parâmetros óticos da Pseudomonas aeruginosa, do meio Asparagina e da suspensão tratada foram medidos de faixa de comprimento de onda de 254 nm. A pressão e temperatura foram a 1 atm e 25ºC, respectivamente. As evoluções dinâmicas da concentração da bactéria e dos parâmetros óticos foram obtidas. Observou-se que o tempo de processo para que esta concentração chegasse a zero aumentou de acordo com a concentração inicial de bactéria, em ambas as situações. Para água-modelo sem nutriente obteve-se a esterilização da água (eficiência de inativação de 100%), no entanto para água-modelo com nutriente obteve-se água desinfetada. Os parâmetros para água-modelo sem nutriente foram invariantes com o tempo, porém para o sistema com nutriente decrescia ao longo do processo. A modelagem do processo foi feita com base nos princípios da conservação da matéria e energia variante. Assumiu-se que o modelo cinético simplificado para a inativação da bactéria em que a taxa de inativação é uma função direta do rendimento quântico, do parâmetro LVRPA, e da concentração inicial de bactéria. O método de Runge-Kutta de quarta ordem foi utilizado para solucionar a equação diferencial do perfil de concentração. Os parâmetros cinéticos foram estimados utilizando-se rotina de otimização Box-Simplex

Zinc oxide nanoparticles are highly variable materials capable of producing positive and negative responses to their effects on plants. Negative effects are often associated with their excessive concentration, which can cause oxidative stress in plants.Conversely, suitable dosages lead to positive manifestations of growth and improvement in the properties studied. ZnO nanoparticles provide plants with a more acceptable form of zinc that is well accessible and easier to use. However, information about their pos-sible toxic effect in combination with another stress factor is lack. The aim of this work was to compare and evaluate the effects of zinc in the form of nanoparticles (ZnO NPs) with the effects of zinc bound in chelate bonding (Zn-EDTA), in combination with UV-C stress factor in plants Solanum lycoperscicum L. Results of this pilot experiment show that both ZnO and Zn-EDTA nanoparticles of 10.95 mg Zn2+ /l in combination with UV-C radiation have a negative effect on vitality and induce oxidative stress in treated plants. The decisive effect on the toxic effect was based on the concentration used and the form of zinc applied. Differences were expres-sed in expression levels of genes affected by oxidative stress. The results obtained from the expression analysis of the genes made it possible to observe the individual transcripts used to respond to oxidative stress and also to provide information on the possible sy-nergistic effect of UV-C radiation and zinc in both studied forms (Zn-EDTA and ZnO NPs).

Submitted by Gabriela Lopes (gmachadolopesufpel@gmail.com) on 2018-08-14T18:24:06Z No. of bitstreams: 1 Dissertação - Cláudia Medeiros Camargo.pdf: 1890787 bytes, checksum: 483a98199d1e25df032841b77b3a5358 (MD5) / Approved for entry into archive by Aline Batista (alinehb.ufpel@gmail.com) on 2018-08-17T12:37:05Z (GMT) No. of bitstreams: 1 Dissertação - Cláudia Medeiros Camargo.pdf: 1890787 bytes, checksum: 483a98199d1e25df032841b77b3a5358 (MD5) / Made available in DSpace on 2018-08-17T12:37:05Z (GMT). No. of bitstreams: 1 Dissertação - Cláudia Medeiros Camargo.pdf: 1890787 bytes, checksum: 483a98199d1e25df032841b77b3a5358 (MD5) Previous issue date: 2017-07-31 / Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul - FAPERGS / O milho (Zea mays L.) ) é o segundo cereal mais produzido no Brasil e sua importância econômica se dá pelas diversas formas de uso e relevância na alimentação humana e animal. Devido à grande demanda de milho pela indústria alimentícia é necessário que os grãos fiquem armazenados por longos períodos para atender o mercado em períodos de entressafra. Durante o armazenamento, algumas espécies de fungos se proliferam em grãos armazenados favorecendo a produção de micotoxinas e tornando-os impróprios para o consumo. Dessa forma, a radiação pode ser um método alternativo de controle dos fungos e, portanto, manutenção da qualidade dos grãos de milho. Sendo assim, o trabalho foi dividido em dois capítulos visando atender a dois objetivos principais: i); ii) avaliar os efeitos da radiação UV-C e da umidade dos grãos nos parâmetros qualitativos e quantitativos tecnológicos dos grãos de milho durante o armazenamento; ii) avaliar os efeitos da radiação UV-C e da umidade dos grãos nos parâmetros qualitativos e quantitativos tecnológicos do amido de milho extraído de grãos armazenados durante o armazenamento. Foram utilizados grãos de milho colhidos mecanicamente e secos até as umidades de 13% e 16%. Os grãos receberam inóculos de fungos produtores de micotoxinas e tratamento com radiação UV-C nas doses de 4 e 8 Kj.m-2. A radiação UV-C nas doses utilizadas não apresentou influencia sobre os resultados obtidos, no entanto a umidade e o tempo de armazenamento influenciaram diretamente nos parâmetros avaliados. A associação de elevada umidade e armazenamento por longo prazo apresentou aumento sobre a incidência dos fungos Aspergillus e Pennicilium, condutividade elétrica, acidez lipídica, grãos mofados, ardidos e fermentados, e redução sobre os fungos do gênero Fusarium, solubilidade proteica, teor de lipídeos e valor L. Os compostos fenólicos apresentaram maior concentração nos grãos inoculados com fungos (0, 4 e 8 kJ.m- 2). As micotoxinas foram encontradas em maior concentração após o armazenamento, sendo favorecidas dose de 8 kJ.m-2 e a umidade de 16%. Não foram observadas alterações na amilose e solubilidade do amido. Após o armazenamento, na umidade de 16% são observadas as maiores alterações, com reduções na extração de amido, valor de L* e aumentos no valor b*, proteína bruta, teor de lipídeos. As propriedades de pasta foram mais influenciadas na umidade de 16%, com aumentos na temperatura de pasta, retrogradação e reduções na viscosidade máxima e viscosidade de quebra. O amido apresentou perfurações em todos os tratamentos, sendo encontradas em maiores concentrações na umidade de 16% na dose de 8kJ.m-2. A radiação promoveu aumento no poder de inchamento dos grânulos de amido em todas as doses em ambas as umidades, sendo os maior aumentos observados na umidade de 16%. / Corn (Zea mays L.) is the second most produced cereal in Brazil and its economic importance is due to the different forms of use and relevance in human and animal food. Because to the high demand of maize by the food industry, it is necessary that the grains are stored for long periods to meet the market in offseason. During storage, some species of fungi proliferate in stored grains favoring the production of mycotoxins and rendering them unfit for consumption. So, radiation can be an alternative method of fungus control and, therefore, maintenance of the quality of corn grains. Therefore, the study was divided into two chapters aimed at meeting two main objectives: i); Ii) to evaluate the effects of UV-C radiation and grain moisture on the qualitative and quantitative technological parameters of corn grains during nine months of storage; Ii) to evaluate the effects of UV-C radiation and grain moisture on the qualitative and quantitative technological parameters of corn starch extracted from grains stored during nine months of storage. Corn grains were harvested mechanically and dried to moisture of 13% and 16% . The grains were inoculated with fungi and treated with UV-C radiation at 4 and 8 KJ.m-2 doses. The UV-C radiation at the doses used did not influence the results obtained, however, moisture and storage time had a direct influence on the evaluated parameters. The association of high moisture and a long time of storage showed an increase in the incidence of fungi Aspergillus and Pennicilium, electrical conductivity, lipid acidity, moldy, arid and fermented grains, and reduction on fungi of the genre Fusarium, protein solubility, lipid content and Value L. The phenolic compounds presented higher concentration in the grains inoculated with fungi (0, 4 and 8 kJ.m-2). The mycotoxins were found in higher concentration after storage, being favored dose of 8 kJ.m-2 and the moisture of 16%. No changes were observed in the amylose and solubility of the starch. After storage, in the moiture of 16% are observed the major changes, with reductions in the extraction of starch, value of L * and increases in value b *, crude protein and lipid content. The pasta properties were most influenced at 16% moisture, with increases in pasta temperature, retrogradation and reductions in maximum viscosity and viscosity break. In all treatments, the starch presented perforations, being found in higher concentrations in the moisture of 16% and the dose of 8kJ.m-2. The radiation promoted an increase in the swelling power of the starch granules in all doses in both moistures, with the highest observed increases in moisture content of 16%.

Appliqués à forte dose, les rayonnements UV-C sont délétères, alors que administrés à faibles doses, ces memes rayonnements stimulent des réponses bénéfiques. Ce phénomène est connu sous le nom d’hormesis et la dose bénéfique est qualifiée d’hormique. L’application des faibles doses d’UV-C sur les fruits et les légumes en post-récolte a permis donc d’augmenter leur résistance vis à vis des pathogènes (Charles et al, 2008), d’améliorer leur qualité nutritionnelle (Mercier et al, 2001) et d’améliorer leur rendement et leur croissance (Siddiqui et al, 2011). Ces travaux ont été réalisés sur des espèces différentes. Dans le cadre de ma thèse, nous avons traité une seule espèce de laitues romaines var Claudius après récolte avec une dose non délétère d’UV-C (0.85kJ.m-2) puis nous avons évalué son effet sur leur aspect de résistance aux champignons Botrytis cinerea (BC87) et Sclerotinia minor (SM), sur leurs valeurs nutritionnelles au cours du stockage et sur leurs réponses à la contrainte saline du milieu. L’analyse de tous les résultats obtenus,a mis en évidence que la dose d’UV-C choisie diminue la sensibilité de la laitue romaine à ces deux agents pathogènes (Ouhibi et al. 2014a), améliore sa valeur nutritionnelle en augmentant la concentration des composées phénoliques et de l’acide ascorbique et acquière aux plantes provenant de grains prétraitées aux UV-C un meilleur potentiel d'adaptation à la contrainte saline (Ouhibi et al, 2014 b). Le traitement des plantes avec une dose d’UV-C non délétère permet d’agir de façon bénéfique et simultanément sur différents processus physiologiques. / Applied in high doses, UV-C radiations are harmful, while administered at low doses, these same radiations stimulate beneficial answers. This phenomenon is known as hormesis and the beneficial dose is qualified hormic. The application of low doses of UV-C on fruits and vegetables in post harvest enhances resistance against pathogens (Charles et al, 2008), improve their nutritional quality (Mercier et al, 2001) and their performance to grow (Siddiqui et al, 2011). This works were carried out on different species. In my thesis, we treated a single species of romaine lettuce var claudius after harvest with a non-harmful dose of UV-C (0.85kJ.m-2) and we evaluated its effect on resistance to Botrytis cinerea (BC87) and Sclerotinia minor (SM), in their nutritional value during storage and their responses to salt stress. The analysis of all the results obtained showed that the UV-C dose decreases the sensitivity of romaine lettuce to these two pathogens (Ouhibi et al. 2014a), improve nutritional value by increasing the content in phenolic compound, in ascorbic acid and acquire to plants from seeds pre-treated with UV-C greater potential for adaptation to salt stress (Ouhibi et al, 2014 b).

La décontamination bactériologique des surfaces par lumière pulsée est un enjeu de société qui requiert le développement de nouveaux outils. Une technique ayant prouvée son efficacité est l’utilisation de lumière pulsée dans le domaine de longueur d’onde 200-280 nm (bande d’absorption de l’ADN). Dans ce travail, nous avons étudié deux sources, Décharge à Barrière Diélectrique (DBD) et réseaux de microdécharges permettant de générer un rayonnement à 222 nm correspondant à l’émission de l’exciplexe KrCl*. Nos études ont permis de démontrer qu’il était possible de produire des décharges dans de nombreuses microcavités fonctionnant en parallèle sans aucun ballast résistif à condition d’employer une excitation impulsionnelle nanoseconde. Des études d’imagerie et de spectroscopie résolues temporellement ont démontré que l’ensemble des microdécharges s’initiaient en moins de 5 ns, ce qui permet d’envisager la réalisation de matrice de microdécharges rayonnant des puissances crêtes élevées. Dans le cas des DBD, les études ont couplé modèle et expérience, ce qui nous a permis de déterminer les étapes clés de la cinétique réactionnelle et de prédire les meilleures conditions de production d’un rayonnement intense à 222 nm. Par ailleurs, grâce aux microdécharges, nous avons pu réaliser une source de rayonnement VUV permettant de sonder la densité de chlore atomique dans des réacteurs de gravure plasma par spectroscopie d'absorption résonnante. / Bacteriological decontamination of surfaces by pulsed light is a society issue that requires the development of new tools. A technique that proved its efficiency was to use a pulsed light in the 200-280 wavelength range corresponding to the DNA absorption band.In this work, we studied two different sources, the so-called Dielectric Barrier Discharge (DBD) and microdischarges arrays, to generate a radiation at 222 nm corresponding to the KrCl* exciplex emission. By using nanosecond pulsed discharges, we demonstrated that many microdischarges operating in parallel can be triggered simultaneously without introducing any resistive ballast. High speed ICCD imaging and time resolved spectroscopic studies had shown that all the microdischarges were initiated in less than 5 ns, which allowed the produce arrays of microdischarges generating high peak power of UV light. In the DBD case, studies have coupled experience and simulation which allowed us to determine the key steps of the kinetic pathways and to predict the best conditions for producing an intense 222 nm radiation. Moreover, microdischarges were also used to realize a VUV source to probe the atomic chlorine density in plasma etching reactors through resonance absorption spectroscopy.

Certains champignons sont très dommageables pour les plantes mais aussi pour la conservation après récolte des produits végétaux. Les restrictions réglementaires concernant l’utilisation des fongicides nécessitent de trouver des solutions alternatives. L'amélioration de la résistance des plantes en utilisant des méthodes physiques, comme les rayonnements UV, peut présenter une alternative prometteuse en association avec d’autres méthodes dans le cadre d’une protection intégrée des cultures. L'objectif de cette thèse a été d’étudier l’effet des rayonnements UV-C sur la sensibilité des plantes aux agents pathogènes. Les rayonnements UV-C ont été appliqués durant la culture, seuls ou en combinaison à des agents de biocontrôle, ou en post-récolte. Les expérimentations ont été menées sur deux espèces végétales : le fraisier et la tomate.Sur fraisier, des traitements UV-C à une dose de 1,70 kJ/m² entraînent une diminution systématique d'environ 20 % de la sensibilité des feuilles à Botrytis cinerea et diminuent jusqu’à 50 % le nombre de feuilles attaquées par Podosphaera aphanis, l’agent causal de l’oïdium. Chez la tomate, la protection des feuilles contre B. cinerea atteint 43 % avec une dose d’UV-C cumulée de 4,0 kJ/m². Ces mêmes traitements UV-C appliqués sur fruits réduisent la sensibilité des fraises vis-à-vis de Rhizopus de 75 % mais aucun effet n’est observé vis-à-vis de B. cinerea. Au contraire, sur fruits de tomate, la sensibilité est diminuée d'environ 63 % contre cet agent pathogène. Parallèlement, des tests biochimiques et gustatifs suggèrent que la qualité des fruits n’est pas significativement améliorée ni altérée par les expositions UV-C. Malgré un effet germicide marqué des rayonnements UV-C sur feuilles de fraisiers, aucun effet bénéfique de l’application de ces rayonnements sur le niveau d’efficacité d’agents de lutte biologique n’a été mis en évidence.Nos observations sont encourageantes pour envisager une utilisation de cette méthode dans un schéma de protection intégrée des cultures. Cependant, une compréhension claire de la façon dont les rayonnements UV-C sont perçus par les plantes et traduits en mécanismes de défense est nécessaire avant que leur utilisation ne soit recommandée sur le terrain. / Some fungi are very damaging during plant cultivation and also in post-harvest storage of products. Regulatory restrictions on fungicide use require alternative solutions. Improving plant resistance using physical methods, such as aplication of UV radiation, can be a promising alternative in association with other methods as part of an integrated pest management strategy. The objective of the present thesis was to study the effect of UV-C aplication on the sensitivity of plants to fungal pathogens. UV-C radiation was applied during plant cultivation, alone or in combination with biocontrol agents, or in post-harvest. Experiments were conducted on two plant species: strawberry and tomato.On strawberry plants, UV-C treatments at 1.70 kJ/m² result in a systematic 20 % decrease in leaves sensitivity to Botrytis cinerea and in a reduction by up to 50 % of the number of leaves infected by Podosphaera aphanis, the causal agent of powdery mildew. In tomato, leaves protection against B. cinerea reaches 43 % with a cumulative dose of 4.0 kJ/m². UV-C treatments applied on fruits reduce the strawberry sensitivity to Rhizopus by 75 % but no effect is observed against B. cinerea. On the contrary, sensitivity against B. cinerea is reduced by 63 % on tomato fruit. Biochemical and taste tests suggest that fruit quality is not significantly improved or altered by UV-C treatment. Despite a marked germicidal effect of UV-C radiation on strawberry leaves, it has no significant effect on the protective efficacy of biocontrol agents.Our observations are encouraging to consider the use of this tool in an integrated crop protection scheme. However, a clear understanding of how UV-C radiations are perceived by plants and their translation into defense mechanisms is necessary before their use is recommended in the field.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Ultraviolet light type C (UV-C) is a non-thermal technology that has been used as an abiotic stressor to delay microbial growth and enhance the phytochemical content of food crops. However, its effects may vary depending on the cultivar, fruit, hormetic dose and time after exposure. Isabella is a hybrid grape cultivar (Vitis labrusca L.) that represents about 50% of Brazilian grape production and is commonly consumed in natura. The effects of UV-C irradiation (0.5, 1.0, 2.0, and 4.0 kJ m-2) followed by storage at 20°C (1, 3, and 5 days) were evaluated on quality indicators, bioactive compounds, antioxidant capacity and phenylalanine ammonia lyase (PAL) activity of Isabella grapes. The highest UV-C doses (2.0 and 4.0 kJ m-2) led to a rapid increase (about 10%) of total soluble solids (TSS) and decrease of pH values (p<0.05). All samples showed an increase on total phenolics (813.6 ± 99.6 in the 1st day vs. 1016.4 ± 79.6 mg gallic acid equivalents 100 g-1 skin FW in the 5th day), flavonols (351.1 ± 58.4 in the 1st day vs. 496.9 ± 83.1 mg quercetin-3-rutinoside equivalents 100 g-1 skin FW in the 5th day), and anthocyanins (215.3 ± 35.4 in the 1st day vs. 272.2 ± 43.5 mg malvidin-3-glucoside equivalents 100 g-1 skin FW in the 5th day) content along the storage (p<0.05). Total phenolic compounds increased after UV-C at 1.0 and 2.0 kJ m-2, whereas anthocyanin content increased after UV-C at 0.5, 1.0, and 2.0 kJ m-2 (p<0.05). The levels of ascorbic acid (AA) and total vitamin C decreased in all samples during the storage (p<0.05). UV-C treatment had no effect on the flavonol content, but decreased AA and total vitamin C content (0.5 - 2.0 kJ m-2, p<0.05). PAL activity decreased along storage time in all samples (47.7 ± 3.6 in the 1st day vs. 38.4 ± 2.7 and 32.4 ± 2.1 104 EAU min-1 mg protein-1 in 3rd and 5th days after treatment, p<0.05). UV-C radiation (0.5-2.0 kJ m-2) increased PAL enzyme activity in two-fold relation to control. UV-C treated grapes had higher antioxidant capacity than control grapes in the ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays (p<0.05). Indeed, this effect was positively correlated to the content of total phenolic and anthocyanin compounds and negatively correlated to ascorbic acid and vitamin C contents (p<0.05). Thus, UV-C radiation can be used to increase bioactive compounds and antioxidant capacity of Isabella grapes, being 1.0 kJ m-2 the most appropriate dose for the studied conditions. UV-C effects appeared immediately after the irradiation and gradually decreased along the storage. / A radiação ultravioleta do tipo C (UV-C) é uma tecnologia não-térmica que está sendo usada como um estressor abiótico para retardar o crescimento microbiano e aumentar o teor de fitoquímicos em culturas de alimentos. No entanto, seus efeitos podem variar dependendo da fruta, da cultivar, da dose hormética e do tempo após a exposição. A Isabel é uma cultivar híbrida de uva (Vitis labrusca L.) que representa cerca de 50% da produção brasileira de uvas e é amplamente usada para consumo in natura. Foram avaliados os efeitos da irradiação com UV-C (0.5, 1.0, 2.0 e 4.0 kJ m-2) seguida pelo armazenamento a 20°C (1, 3 e 5 dias) sobre indicadores de qualidade, compostos bioativos, capacidade antioxidante e atividade da fenilalanina amônia liase (FAL) de uvas Isabel . As maiores doses (2.0 e 4.0 kJ m-2) levaram a um rápido aumento dos sólidos solúveis totais (SST) (cerca de 10%) e a um decréscimo dos valores de pH (p<0,05). Todas as amostras apresentaram um aumento no teor de fenólicos totais (813,6 ± 99,6 no 1° dia vs. 1016,4 ± 79,6 mg ácido gálico 100 g-1 casca em peso fresco no 5° dia), flavonois (351,1 ± 58,4 no 1° dia vs. 496,9 ± 83,1 mg quercetina-3-rutinosídeo 100 g-1 casca em peso fresco no 5° dia) e antocianinas (215,3 ± 35,4 no 1° dia vs. 272,2 ± 43,5 mg malvidina-3-glicosídeo 100 g-1 casca em peso fresco no 5° dia) ao longo do armazenamento (p<0,05). Os compostos fenólicos totais aumentaram após a irradiação com UV-C nas doses de 1.0 e 2.0 kJ m-2, enquanto o teor de antocianinas aumentou após irradiação com as doses 0,5, 1.0 e 2.0 kJ m-2 (p<0,05). Os teores de ácido ascórbico (AA) e vitamina C total diminuíram em todas as amostras durante o armazenamento (p<0,05). O tratamento com UV-C não teve efeito sobre o teor de flavonois, mas diminuiu o teor de AA e vitamina C total (0,5-2.0 kJ m-2, p<0,05). A atividade da FAL diminuiu ao longo do armazenamento em todas as amostras (47,7 ± 3,6 no 1° dia vs. 38,4 ± 2,7 e 32,4 ± 2,1 104 EAU min-1 mg proteína-1 no 3° e 5° dias após o tratamento, p<0,05). A radiação UV-C (0,5-2.0 kJ m-2) aumentou a atividade da enzima FAL em 2 vezes em relação ao controle. As uvas tratadas com UV-C tiveram maior capacidade antioxidante nos ensaios do poder antioxidante de redução do ferro (FRAP) e de remoção do radical 2,2-difenil-1-picril-hidrazil (DPPH) que as uvas controle (p<0,05). Além disso, este efeito antioxidante foi positivamente correlacionado ao teor de compostos fenólicos totais e antocianinas e negativamente correlacionado ao teor de ácido ascórbico e vitamina C total (p<0,05). Assim, a radiação UV-C pode ser usada para aumentar o teor de compostos bioativos e a capacidade antioxidante de uvas Isabel , sendo 1.0 kJ m-2 a dose mais apropriada nas condições estudadas. Os efeitos da UV-C apareceram imediatamente após a irradiação e diminuíram gradualmente ao longo do armazenamento.