Made available in DSpace on 2014-06-11T19:30:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-10-31Bitstream added on 2014-06-13T20:20:44Z : No. of bitstreams: 1 oliveirajunior_ef_me_botfca.pdf: 572534 bytes, checksum: e38ab203dda383ef6320ffa9a9d4833c (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O estudo das propriedades físicas e químicas da madeira possibilita um melhor aproveitamento das suas potencialidades. O aproveitamento da madeira de seringueira Hevea brasiliensis após o declínio da produção de látex tem relevância mundial. Uma parte da madeira da seringueira vem de uma área significativa do fuste submetida ao processo de extração de látex. Esse trabalho tem como objetivo analisar as características químicas e físicas da madeira proveniente da região submetida ao processo de extração de látex e compará-la a madeira originária da região que não sofreu processo de extração de látex. Foram utilizadas árvores de seringueira com 53 anos de idade, submetidas ao processo de extração de látex durante 45 anos ininterruptos. Foram realizadas as seguintes análises químicas: determinação do teor de holocelulose, do teor de lignina e teor de extrativos totais. Foram determinadas as seguintes propriedades físicas: densidade, contração volumétrica, contrações lineares e coeficiente de anisotropia. Não foram encontradas diferenças estatísticas entre as propriedades químicas das duas regiões do fuste analisadas nem entre os diferentes tipos de lenho juvenil e adulto. Em relação às propriedades físicas não foram encontradas diferenças entre as regiões estudadas, mas em relação ao tipo de lenho juvenil e adulto ocorrem diferenças estatísticas entre os coeficientes de contrações lineares e contração volumétrica / The study of physical and chemical properties of wood allows a better use of its potential. The use of wood from rubber tree Hevea brasiliensis after the decline of the production of latex has global significance. A portion of the rubber wood is a significant area of the stem submitted to the extraction process latex paper aims to analyze the chemical and physical characteristics of the wood from the region subjected to the process of extracting latex and compares it to wood originally from the region that has not undergone the process of extraction of latex. Rubber trees were used with 53 years old, subject to the latex extraction process for 45 consecutive years. We made the following chemical analysis: determination of holocellulose, lignin content and the content of total extractives. We determined the following properties: density, volumetric shrinkage, linear shrinkage and coefficient of anisotropy. There were no statistical differences between the chemical properties of both the stem region analyzed or between different types of juvenile and adult wood. Regarding the physical properties no differences were found between the regions studied, but in relation to the type of juvenile wood and adult wood statistical difference between the coefficients of linear shrinkage and shrinkage were found

Made available in DSpace on 2014-06-11T19:30:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-08-17Bitstream added on 2014-06-13T19:00:14Z : No. of bitstreams: 1 faragoescobar_j_me_botfca.pdf: 867288 bytes, checksum: 4fd2465a07c814ad9739c937eb618889 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A cultura da seringueira está se firmando como uma atividade lucrativa e sustentável, apresentando um expressivo crescimento em suas áreas de plantio no Brasil. Estabelecidos com o objetivo principal de produção do látex, os seringais apresentam, ao final desse ciclo, boas perspectivas como fornecedores de matéria-prima para o segmento de produtos de madeira sólida. Estudos já realizados mostraram a viabilidade técnica de laminação (a quente e também a frio) de toras de Hevea brasiliensis, para a produção de compensados, como opção de aproveitamento com maior valor agregado dessa madeira. Este trabalho teve como objetivo principal avaliar o desempenho físico-mecânico de painéis compensados de Hevea brasiliensis (clone RRIM 600) confeccionados com lâminas classificadas pelo método não destrutivo das ondas de tensão em classes de desempenho mecânico (baixo, médio e alto módulo de elasticidade dinâmico relativos). As avaliações foram realizadas em painéis compensados confeccionados com lâminas de 2,3 mm de espessura, produzidos na Indústria de Compensados Caribea Ltda. localizada no município de São Manuel, São Paulo - Brasil. Com os mesmos equipamentos e variáveis gerais do processo de fabricação dos compensados foram confeccionados três painéis compensados de nove lâminas para cada um dos cinco arranjos assim definidos: T1 – homogêneo baixo (painéis produzidos somente com lâminas de baixo módulo de elasticidade dinâmico); T2 – combinado baixo (painéis produzidos com lâminas de alto módulo de elasticidade dinâmico na face e contra-face e baixo módulo de elasticidade dinâmico no miolo); T3 - alternado (painéis produzidos com lâminas alternadas de alto e baixo... / The cultivation of rubber tree has been settled in as a profitable and sustainable activity, with a significant growth in planted areas in Brazil. Established with the main objective of production of latex, rubber tree plantations have, at the end of this cycle, good prospects as suppliers of raw material for the segment of solid wood products. Previous studies have shown the technical viability for log lamination (hot and cold processes) of Hevea brasiliensis, for plywood production, as an option of higher added value product. This study evaluated physical and mechanical performance of plywood of Hevea brasiliensis (clone RRIM 600) made with graded veneers (stress wave method) in stiffness classes (low, medium and high dynamic modulus of elasticity). Mechanical evaluations were conducted on plywood made with nine 2.3mm thick veneers, produced in the Indústria de Compensados Caribea Ltda, in São Manuel, São Paulo - Brazil. Plywood were made using the same equipment and general variables of the manufacturing process adopted by this industry, considering five arrangements: T1 – homogeneous low (plywood produced with only low dynamic modulus of elasticity veneers); T2 – combined low (plywood produced with high dynamic modulus of elasticity veneers in the face and back and low dynamic modulus of elasticity veneers in the inner); T3 – alternate (plywood produced with alternated quality veneers - high and low modulus of elasticity); T4 – homogeneous medium (plywood produced with only medium dynamic modulus of elasticity veneers); T5 – combined medium (plywood produced with high dynamic... (Complete abstract click electronic access below)

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Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2014-09-29T12:27:26Z No. of bitstreams: 2 Oliveira , Augusto Pedroso de-2012-Dissertação.pdf: 1221394 bytes, checksum: 3f53224e0b239d497b0f70bbf3b0393e (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2014-09-29T15:07:22Z (GMT) No. of bitstreams: 2 Oliveira , Augusto Pedroso de-2012-Dissertação.pdf: 1221394 bytes, checksum: 3f53224e0b239d497b0f70bbf3b0393e (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2014-09-29T15:07:22Z (GMT). No. of bitstreams: 2 Oliveira , Augusto Pedroso de-2012-Dissertação.pdf: 1221394 bytes, checksum: 3f53224e0b239d497b0f70bbf3b0393e (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2012-06-15 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / To produce rubber tree (Hevea brasiliensis) seedlings in nursery, the collection is limited by the short fall of seeds, which have a rapid loss of their germinal power and no guarantee their viability. This forces the nurseryman to acquire a much larger seeds than really necessary. With the adoption of standards for the quality of seed, the minimum parameters established 70% viability being suggested for such confirmation the tetrazolium test, according Rules for Seed Analysis (RSA) and/or a practical test done from the visual analysis of the seed endosperm color named in this work of "visual test". Despite tetrazolium test be scientifically based, its realization is made improbable by many financial and temporal reasons. Thus, the visual test points as a low-cost alternative, high reliability and immediate result, since both tests are considered trusted, but only the test tetrazolium test is recognized. The subject proposed to verify the credibility of the "visual test" legitimizing or not its use in the field. The field is composed of rubber seed, formed with the adult clone GT1. The seeds were homogenised and stored on two conditions: braided polypropylene bags and transparent plastic bags with minimum thickness of 0.02 mm microdrill at top. In each bag, in three treatments were placed ten kilograms of seed and these were stored in natural conditions of temperature and humidity (25° C ± 5 °C). Was pulled randomly a bag of seeds of rubber tree of each storage type, to zero and fourteen days of storing lots. The tests: visual, sprouting in sand and tetrazolium, besides the determination of the degree of moisture. Tetrazolium and visual tests were highly correlated, and the visual test results before had as the best way to analyze the seeds, for its significant correlation in General with the tetrazolium test, and simplicity in its execution and instant result, which gives good lot projection nurseryman to be acquired by him. / A produção de mudas de seringueira (Hevea brasiliensis) em viveiro, é limitada pelo curto período de produção, queda e coleta das sementes, que possuem uma rápida perda do seu poder germinativo e nenhuma garantia da sua viabilidade. Isto obriga o viveirista a adquirir uma quantidade de sementes maior do que aquela realmente necessária. Com a aprovação de normas para o padrão de qualidade de semente, se estabeleceram parâmetros mínimos de 70% de viabilidade sendo sugerido para tal confirmação o teste de tetrazólio, segundo as Regras para Análise de Sementes (RAS) e, ou, um teste prático feito a partir da análise visual da cor do endosperma da semente nomeado no presente trabalho de “teste visual”. Apesar do teste de tetrazólio ser embasado cientificamente, sua realização é inviabilizada por diversos motivos de ordem financeira e temporal. Sendo assim, o teste visual aponta como uma alternativa de baixo custo, alta confiabilidade e resultado imediato, já que ambos os testes são considerados confiáveis, mas apenas o teste de tetrazólio é reconhecido. Nesta pesquisa objetivou-se verificar a credibilidade do “teste visual” legitimando ou não seu uso no campo. As sementes de seringueira foram coletadas no município de Goianésia, estado de Goiás. O campo de sementes é constituido de seringal adulto, formado com o clone GT1. As sementes foram homogeneizadas e armazenadas em duas condições: sacos de polipropileno trançado e sacos plásticos transparentes com espessura mínima de 0,02 mm, microperfurados na parte superior. Em cada saco, nos dois tratamentos, foram colocados dez quilogramas de sementes e estes foram armazenados em condições naturais de temperatura e umidade (25° C ± 5 °C). Foi retirado aleatoriamente um saco de sementes de seringueira de cada tipo de armazenamento, no tempo zero e aos quatorze dias de armazenamento dos lotes de sementes coletados. Foram realizados os testes: visual, de germinação em areia e de tetrazólio, além da determinação do grau de umidade. Os testes visual e de tetrazolio foram altamente correlatos. O teste visual apresentou a melhor forma de análise das sementes, por sua significativa correlação no geral com o teste de tetrazólio, além da simplicidade em sua execução e resultado instantâneo, o que confere ao viveirista uma boa projeção do lote de sementes a serem adquiridas para a produção de mudas de seringueiras

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A produção de borracha natural de seringueira (Hevea brasiliensis) é uma atividade estratégica para a economia nacional. O principal fator redutor da produtividade dessa atividade é a ocorrência de doenças no seringal. O nematoide de galhas (Meloidogyne exigua) é a principal doença radicular dessa cultura no Brasil e sua identificação antecipada permite um melhor manejo desta epidemia no seringal e a redução de seus prejuízos. O objetivo desse estudo foi identificar áreas com a ocorrência de M. exigua em seringais através do uso dos índices espectrais de vegetação - Índice de Vegetação por Diferença Normalizada (NDVI) e Índice de Razão Simples (RS) - gerados a partir de imagens da constelação de satélites RapidEye® (resolução de 5 metros). Seringais produtivos, com pelo menos 7 anos de plantio, em Minas Gerais (irrigado) e em Goiás (não irrigado) foram amostrados e georreferenciados na segunda metade do período das chuvas e as densidades de nematoides no solo, nas raízes e total foram estimadas. O seringal em Minas Gerais foi amostrado inicialmente seguindo as anormalidades evidenciadas pelo índice NDVI gerado através de imagens do satélite Landsat 8 (resolução de 30 metros). O seringal em Goiás foi amostrado aleatoriamente com o intuito de validar os resultados observados no seringal em Minas Gerais. Apesar de serem identificadas regressões significativas com o uso de imagens de alta resolução (RapidEye®) entre as variáveis densidades de nematoides e os índices espectrais de vegetação, nenhuma apresentou coeficiente de determinação (R2) superior a 0,31. A estatística descritiva do conjunto de dados de ambos os seringais não identificou diferenças entre as áreas para as densidades de nematoides encontradas nas raízes ou a densidade total, no entanto, a densidade de nematoides no solo foi aproximadamente 236% superior no seringal em Goiás, enquanto que ambos os índices neste seringal foram inferiores aos índices estimados para o seringal em Minas Gerais. Está diferença foi consequência da irrigação na área em Minas Gerais. As correlações de Pearson, Spearman e Kendall foram calculadas para as densidades de nematoides e os índices espectrais. As correlações entre a densidade de nematoides do seringal e o índice NDVI foram as que apresentaram os maiores coeficientes significativos para qualquer das correlações avaliadas. Através do índice NDVI é possível diferenciar um seringal não infestado de um seringal infestado pelo nematoide de galhas M. exigua. / The production of natural rubber from rubber trees (Hevea brasiliensis) is a strategic activity for Brazilian economy. The main factor reducing productivity of this activity is the occurrence of diseases in the rubber plantation. The root-knot nematode (Meloidogyne exigua) is the main root disease of this culture in Brazil and its early identification enables better management of its outbreak in orchards and the reduction of their losses. This study identified areas with the occurrence of M. exigua in rubber plantations through the use of spectral vegetation indices - Normalized Difference Vegetation Index (NDVI) and Simple Ratio Index (SR) - generated from images of the constellation RapidEye® satellites (5 meters resolution). Productive rubber plantations, at least 7 years old, in Minas Gerais (irrigated) and Goiás (non-irrigated) states were sampled and georeferenced in the second half of the rainny season and the quantities of nematodes in soil, roots and total were estimated. The rubber plantation in Minas Gerais was sampled initially following the abnormalities detected by the NDVI index generated through the images of Landsat 8 satellite (30 meters resolution). The rubber plantation in Goiás was sampled randomly to validate the results observed in the first rubber plantation (Minas Gerais). In spite of the identification of significant regressions with the use of high resolution images (RapidEye®) between the variables quantities of nematodes and spectral vegetation indices, none showed a coefficient of determination (R2) greater than 0.31. The descriptive statistics of the data set from both surveys did not identify differences in the quantities of nematodes found in the roots or the total quantity between the areas, however, the amount of nematodes in the soil was approximately 236% greater in Goiás rubber plantation, while both spectral vegetation indices (NDVI and SR) in this rubber plantation were lower than the indices estimated for the rubber plantation in Minas Gerais. This difference was a result of irrigation in the area in Minas Gerais. The correlations of Pearson, Spearman and Kendall were calculated between the densities of nematodes and the spectral vegetation indexes. The correlations between the amount of nematodes in rubber trees plantation and NDVI index showed the best significant coefficients for any of the correlations evaluated. Through the NDVI index it is possible to differentiate an infested rubber tree plantation from a non-infested rubber tree plantation by M. exigua root-knot nematode. / Tese (Doutorado)

Dans un contexte de changements climatiques, le stress hydrique et la gestion de l'eau sont considérés comme une contrainte importante pour le secteur agricole. Ainsi la sélection pour la tolérance à la sécheresse est devenue un objectif majeur pour de nombreux programmes de sélection. La vulnérabilité à la cavitation est considérée comme un trait d'intérêt pour la sélection à une sécheresse extrême, en particulier pour les plantes ligneuses. Pourtant, l'étendue de sa variabilité et sa relation avec la tolérance à la sécheresse sont mal documentées à l’échelle intra-spécifique, et en particulier dans les espèces cultivées. Dans cette étude, la variabilité génétique de la vulnérabilité à la cavitation a été étudiée sur trois dispositifs expérimentaux différents avec trois arbres d’intérêt agronomique qui sont menacés par le risque de sécheresse: noyer, hévéa et pommier. Une faible ou aucune, variation de la vulnérabilité à la cavitation a été trouvée dans les espèces étudiées ainsi qu'entre deux espèces de noyers malgré les différences de traits précédemment rapportés. Ces résultats suggèrent une canalisation de la résistance à la cavitation dans les organes critiques (branches, tiges). Chez le pommier, le porte-greffe est soupçonné de provoquer de la plus étroite résistance à la cavitation sur le greffon. Par contre, des différences ont bien étés trouvées sur d’autres traits de réponse à la sécheresse comme la régulation stomatique, la chute des feuilles ou encore la vulnérabilité à la cavitation dans le pétiole. Ainsi, la vulnérabilité à la cavitation des organes critiques n’est pas un paramètre pertinent pour la sélection de la tolérance à la sécheresse, et les programmes de sélection sur les espèces étudiées ne semblent pas avoir affecté ce paramètre. / In a context of climatic changes, drought stress and water management are regarded as one of the most important constraints for agricultural sector. Thus the selection for drought tolerance became a main objective for many breeding programs. Vulnerability to cavitation is considered a trait of interest for the selection for extreme drought stress, especially for woody species. However, the extent of its variability and its relation to drought tolerance are poorly documented on intraspecific level, particularly for cultivated species. In this study the genetic variability of vulnerability to cavitation was studied on three different experimental devices with three trees of agronomic interest that are threatened by the risk of drought: walnut, rubber and apple trees. Low or no variation in xylem vulnerability to cavitation was found in the studied species and between two species of walnuts despite differences previously reported features. These results suggested a canalization of cavitation resistance on critical organs (branches and stems). In apple tree, the rootstock was suspected to cause the narrow resistance to cavitation on the scion. On the contrary, differences on other traits in response to drought stress such as stomatal regulation, leaf shedding or vulnerability to cavitation on petiole were found. Therefore, vulnerability to cavitation of critical organs was not a relevant parameter for the selection of drought tolerance and breeding programs on the species studied did not appear to affect this parameter.

Pour d'évidentes raisons agronomiques et environnementales, être en mesure de concevoir et mettre en place des systèmes de culture dans lesquels les plantes accèdent aux ressources de manière optimale revêt une importance cruciale pour tous les intervenants impliqués dans la production agricole. Les techniques d'intensification telles que la mise en place de cultures d'inter-rang et l'agro-foresterie visent à accroître la productivité globale des terres tout en assurant la durabilité des agro-écosystèmes, via une optimisation de l'utilisation des ressources environnementales (lumière, eau et nutriments) par les plantes et une préservation des cycles géochimiques. En théorie, les moyens d'atteindre ces objectifs sont nombreux mais en pratique, les interactions souterraines sont complexes et difficiles à mesurer, de sorte que les progrès réalisés dans la conception d'agro-écosystèmes améliorés et durables demeurent modestes. Dans ce contexte, l'objectif de ce travail a été d'évaluer, au travers de mesures racinaires detaillées en rhizotron et au champ, les effets des cultures d'inter-rang sur la croissance des jeunes hévéas. La dynamique des interactions souterraines a été étudiée, tant au niveau de la racine individuelle qu'à celui du système racinaire entier, sur la base, notamment, de descriptions numériques détaillées. Une telle approche a permis de proposer, en outre, une voie novatrice pour l'analyse de la dynamique racinaire à l'echelle du systeme racinaire entier, à savoir l'analyse des trajectoires de croissance. Dans le cas de l'association maïs-hévéa, les expérimentations en rhizotron ont permis de mettre en evidence que les interactions souterraines entre ces deux plantes peuvent induire des modifications de la croissance de leurs racines, à la fois à l'échelle de la racine individuelle et à celle du système racinaire entier. Toutefois, une telle coordination des dynamiques racinaires des plantes associées n'a pas pu être confirmée dans le cas des traitements manioc-hévéa et arachide– hévéa. Les expérimentations au terrain ont fourni, de manière assez prévisible, une image complexe des interactions souterraines entre hévéa et cultures d’inter-rang. Toutefois, un premier résultat obtenu par le biais de la mise en place de 'pièges à racines' dans un traitement niébé-hévéa, a été de montrer que ces deux plantes n'avaient pas un comportement compétitif marqué l'une vis-à-vis de l'autre. Il est également apparu que les hévéas paraissent ‘investir’ dans des racines ‘coûteuses’, car de faible longueur spécifique, probablement pour assurer une certaine durabilité de ces organes, tandis que les cultures d’inter-rang favorisent l'allocation des assimilâts vers des racines de longueur spécifique élevée, de construction moins ‘coûteuses’, probablement en réponse a un impératif de croissance plus rapide (suggéré par les taux d’élongation racinaire mesurés au cours des expérimentations en rhizotron). Enfin, excepté le cas du manioc, l’introduction de cultures d’inter-rang telles que le maïs et l'arachide n'a pas eu d'impact significatif sur le développement des jeunes hévéas, comme en attestent l'évolution de leur circonférence, hauteur et développement foliaire. Ce résultat de terrain est compatible avec les résultats des expérimentations en rhizotron qui n'ont démontré aucun effet inhibiteur des cultures d’inter-rang sur le développement de la partie aérienne des hévéas. Bien que les travaux présentés dans ce rapport, ne permettent pas, à eux seuls de conclure de manière définitive sur la façon dont les espèces cultivées en association peuvent se compléter mutuellement sur le plan fonctionnel, ils apportent des éléments de réponse préliminaires à cette question complexe ainsi que des méthodes permettant de les obtenir. Au total, ce travail représente donc une contribution à la conception des agro-écosystèmes durables qui deviennent de plus en plus indispensables dans le contexte d'une demande mondiale croissante en produits alimentaires et matières premières. En outre, certains des résultats obtenus dans le cadre de cette thèse ouvrent des perspectives pour des recherches plus approfondies, avec une finalité agronomique appliquée / For obvious agronomic and environmental reasons, being able to design and implement agro-ecosystems in which crops have optimal access to resources is of pivotal importance to all stakeholders involved in agricultural production. Intensification techniques such as agro-forestry or the introduction of inter-crops aim to increase land productivity while conserving geochemical cycles, to ensure the sustainability of agro-ecosystems through an optimized use of environmental resources (light, water and nutrients). In theory, there are many ways of achieving such a goal, but in practice, below-ground interactions between plants are complex and difficult to measure, so that progress with the development of sustainable agro-ecosystems has been slow and remains modest. In this context, the objective of this work was to assess the effects of inter-crops on the growth of young rubber trees, based on a detailed analysis of below-ground interactions between the associated plants. The dynamics of below-ground interactions has been studied in rhizoboxes, at both the scale of individual roots and that of the whole root system, using detailed numerical descriptions of root architecture. Such an approach resulted in the design of an innovative method for the analysis of the entire root system dynamics, namely, the analysis of growth trajectories. In the case of the maize-rubber tree association, the experiments in rhizoboxes showed that the below-ground interactions between these two plants can induce changes in root growth, at both the individual root and the whole root system levels. However, such a coordination of rooting patterns could not be confirmed in the case of the cassava-rubber tree and groundnut-rubber tree associations. Not unexpectedly, field experiments provided a rather complex picture of the underground interactions between rubber trees and inter-crops. However, initial results obtained using 'root traps' in a cowpea-rubber tree treatment indicated that these two plants were unlikely to have a marked underground competitive behavior relative to each other. Results of field experiments also indicated that, in general, rubber trees seem to 'invest' in 'expensive roots' of low specific root length, presumably to confer some degree of durability to these organs, while inter-crops favoured the allocation of assimilates to 'cheaper' roots, i.e. roots of much higher specific length, probably in response to a 'fast growth imperative' (an hypothesis supported by the root elongation rate values measured during the rhizobox experiments). Finally, to the possible exception of cassava, inter-crops were found to have no significant impact on the development of young rubber trees, as evidenced by measured changes in tree circumference, height and leaf development. This result is consistent with results from the rhizobox experiments which also showed no inhibitory effect of inter-crops on the above-ground development of rubber trees. Although the work presented in this report does not allow, in itself, to conclude firmly on the issue of the functional complementarity between plants grown in association in inter-cropping systems, they provide preliminary answers to this complex issue together with methods to obtain such answers. Overall, this work therefore represents a contribution to the design of sustainable agro-ecosystems which are becoming increasingly needed in the context of a growing global demand for food and raw materials. In addition, some of the results generated by this work open up prospects for future research for the development of sustainable agro-ecosystems

Menace potentielle pour l'hévéaculture mondiale, la maladie sud-américaine des feuilles de l'hévéa provoquée par le champignon Microcyclus ulei est aussi responsable du faible développement de cette culture en Amérique latine. La sélection de variétés résistantes est privilégiée pour anticiper une apparition accidentelle de la maladie dans les pays encore épargnés et pour développer la culture de l'hévéa dans les zones infestées. La principale source de résistance décrite jusqu'à présent n'est pas fonctionnelle face à des isolats très agressifs du champignon. Une autre source de résistance identifiée chez un cultivar originaire du Pérou se maintient depuis plus de trente ans en conditions de forte infestation. La cartographie génétique réalisée sur la descendance de ce cultivar en croisement révèle l'existence de deux gènes majeurs de résistance, l'un situé sur le groupe de liaison g15 et efficace contre les isolats de Guyane et l'autre sur le groupe de liaison g13 efficace vis-à-vis des isolats de l'état de Bahia. L'analyse de la diversité des populations naturelles du sud-ouest Amazonien fait apparaître une structure en trois groupes principaux recouvrant les états brésiliens de l'Acre, du Rondônia et du Mato Grosso. La population Madre de Dios au Pérou est rattachée au groupe de l'Acre. La différentiation entre les populations est expliquée principalement par l'isolement par la distance et secondairement par l'existence de bassins hydrographiques. Le déséquilibre de liaison entre marqueurs liés est plus étendu dans le groupe Acre que dans le groupe Rondônia, mais reste faible dans les deux cas. Une association avec le caractère de résistance à M. ulei est détectée avec un marqueur microsatellite situé à proximité du gène majeur de résistance du groupe de liaison g15. Une autre association est détectée dans une portion du génome où aucun locus de résistance n'était identifié jusqu'à présent. L'importance de ces résultats pour la sélection de nouveaux cultivars résistants à M. ulei est discutée.

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L'hévéa (Hevea brasiliensis) est actuellement la seule source commerciale de caoutchouc naturel. Parmi les maladies affectant l'hévéa, la CLF (" Corynespora Leaf Fall ") causée par le champignon Corynespora cassiicola, est devenue en une cinquantaine d'années un fléau pour l'ensemble des pays hévéicoles d'Asie et d'Afrique. Actuellement, la gestion du problème consiste à arracher les clones les plus sensibles et à traiter les arbres avec des fongicides en cas d'épidémie. Cependant, le nombre de clones touchés par la maladie ne cessant d'augmenter, il devient urgent de sélectionner de nouveaux clones à la fois tolérants et aptes à la production. Nos travaux ont permis de caractériser le gène codant la cassiicoline, toxine protéique glycosylée secrétée par C. cassiicola, et d'analyser sa diversité. Une étude comparative portant sur trois isolats de C. cassiicola d'agressivité contrastée a montré la présence du gène Cas1 chez les isolats de forte et moyenne agressivité, alors qu'il n'est pas détecté chez l'isolat de faible agressivité. Les niveaux d'agressivité des isolats sont corrélés aux niveaux de transcrits du gène de cassiicoline. Le rôle de la cassiicoline serait prépondérant dans les phases précoces de l'infection. L'analyse de diversité du gène de cassiicoline à partir d'une collection d'isolats provenant de différents hôtes et d'origines géographiques variées, a révélé l'existence d'au moins six isoformes protéiques (Cas1 à Cas6). La structuration génétique globale des isolats basée sur des marqueurs neutres est similaire à la structuration basée sur le gène de cassiicoline. Les isolats prélevés sur hévéa se regroupent en clades spécialisés, dont un correspondant aux isolats porteurs du gène Cas1, identifiés comme étant les plus agressifs sur hévéa. Cependant, 58 % des isolats testés semblent dépourvus de gène de cassiicoline, bien que certains génèrent des symptômes modérés sur hévéa, ce qui suggère l'existence d'autres effecteurs. Des formes endophytiques de C. cassiicola ont été isolées à partir de feuilles asymptomatiques provenant du Brésil, zone encore indemne de CLF. Les gènes de cassiicoline portés par ces souches (isoformes Cas3 et 4) ne semblent pas exprimés lors de l'interaction avec l'hévéa. Nous avons montré par ailleurs que les champignons endophytes de l'hévéa appartenant aux genres Trichoderma et Xylaria présentent une forte activité mycoparasitaire sur C. cassiicola, in vitro. Ces travaux ouvrent de nouvelles perspectives pour le contrôle de la maladie (diagnostic précoce, sélection de clones tolérants, lutte biologique).