L’introduction de biodiversité végétale dans les agroécosystèmes peut modifier la structure des réseaux trophiques du sol et les fonctions écosystémiques qu’ils assurent. Cette thèse fixe les bases d’une démarche expérimentale pour sélectionner des espèces végétales à partir de différents traits fonctionnels et pour évaluer leurs effets sur les réseaux trophiques et le fonctionnement des sols. Nous avons plus particulièrement cherché à sélectionner des plantes de services pouvant induire la régulation des nématodes parasites du bananier Radopholus similis et Pratylenchus coffeae et favoriser la décomposition des matières organiques durant l’interculture dans les bananeraies antillaises. C'est-à-dire la période entre la destruction de la bananeraie et l'implantation d'une nouvelle. Au cours de ce travail, les réseaux trophiques du sol ont été appréhendés par une analyse fonctionnelle des communautés de nématodes. Une étude bibliographique nous a permis de montrer que les traits fonctionnels « statut d’hôtes » vis-à-vis des nématodes phytoparasites, « composition biochimique des litières » et « productivité primaire des espèces végétales » contribuent aux effets des plantes sur les réseaux trophiques du sol et sur les deux services écosystémiques étudiés. Nous avons donc effectué une typologie des plantes de services à partir de ces traits. Puis pour étudier les effets d’apports de litières de composition biochimique contrastée sur les communautés de nématodes du sol, nous avons sélectionné les espèces végétales Paspalum notatum, Crotalaria zanzibarica et Acacia auriculiformis dont les litières présentaient des teneurs variables en hémicellulose, cellulose, azote, et lignine. Une étude en microcosmes a montré que la composition biochimique des litières détermine les successions écologiques au sein des communautés de nématodes et stimule de manière contrastée les voies de décomposition de la matière organique dans les sols. Nous avons discuté des mécanismes de régulation des nématodes parasites du bananier induits par ces apports de litières. Nous avons également montré que la culture de ces trois espèces induit une diminution des populations de R. similis dans les sols. Enfin, nous avons évalué les effets au champ de couverts de P. notatum, de C. zanzibarica et d’un couvert associant ces deux espèces. Pour cela, nous avons cultivé ces couverts durant neuf mois avant de les détruire et de restituer leurs litières à la surface des sols. Nos résultats montrent que ces couverts végétaux influencent différemment l’abondance en nématodes phytoparasites et le potentiel infectieux du sol. Ils induisent également des régulations bottum-up et top down dans leurs communautés. Après la restitution des litières, nous avons observé de fortes abondances de nématodes liées à la décomposition des litières dans la couche de surface du sol. Celle-ci fournit les couches sous-jacentes du sol en azote minéral et favorise le développement des nématodes omnivores et prédateurs. Il en résulte la formation de communautés de nématodes structurées et diversifiées concomitantes à la réduction des populations de R. similis et P. coffeae. Ces résultats étaient plus marqués pour les couverts monospécifiques de C. zanzibarica et les couverts mixtes. Nos travaux confirment que les traits fonctionnels « statut d’hôte », « production primaire », « composition biochimique des litières » sont déterminant pour sélectionner des plantes de services pour l’interculture en bananeraies. / Increased plant diversity may alter soil food web structure and soil function in agroecosystems. This thesis sets the basis for an experimental approach in order to select some plant species in regard to several functional traits and to assess their effect on soil food web and soil functioning. We focused on cover-crops able to induce regulation of the banana parasitic nematodes Radopholus similis and Pratylenchus coffeae and to promote decomposition of organic matter during the fallow period in banana plantations in the French West Indies (FWI). We used functional analysis of nematode communities as a soil food web bio-indicator. Bibliography studies show us that “plant host status” with respect to plant-parasitic nematodes, “biochemical characteristics of litters” and “primary productivity of plants” are functional traits involved in plant species effects on soil food web and on the ecosystemics service we targeted. We therefore use those traits to perform a typology of cover-plants. Furthermore, to study the effects of litter inputs with contrasted biochemical characteristics we pick out the plant species Paspalum notatum, Crotalaria zanzibarica and Acacia auriculiformis which show differential hemicellulose, cellulose, lignin and nitrogen content. A microcosm assay shows that biochemical characteristics of litter determine ecological successions in nematode communities and promote, in a contrasted manner, the decomposition pathway of organic matter. We discussed the mechanisms of plant parasitic nematodes suppression involved by those litter inputs. We also confirm that the culture of those three plant species can diminish the population of R.similis in soils. We also assessed the effects of plant covers composed of P. notatum and C. zanzibarica and a mix of those two plant species on nematodes communities during a field trial. In order to do so, we cultivated those cover-plants during a nine months period and then destroyed them to restitute plant litter in soils surface. Our results showed that cover-plant alters differentially plant-parasitic nematodes and the infectious potential of soils. Cover-crop cultivation also induced bottom-up and top-down regulations in plant parasitic nematode communities. After litter restitution, we observed high abundance of nematodes involved in litter decomposition within the soil surface layer. The latter provides underlying soil layers with mineral nitrogen and improves omnivore and predator nematode abundances. It results in the formation of a structured and diversified nematode community concomitantly with R. similis and P. coffeae regulation in soils. We observed greater effects with the cover-crop composed of C. zanzibarica and the mix of C. zanzibarica and P. coffeae. This study confirms that the functional traits of “host status”, “biochemical composition of litter” and “primary production” of plant species are decisive in the selection of cover-crop for the fallow period in banana plantation.

A possibilidade da compreensão de como vivem os agricultores, quais são seus objetivos, conjunturas políticas e econômicas, valores, crenças e experiências no espaço no qual estão inseridos pode responder a questão que está estreitamente relacionada com a maneira como os agricultores organizam e pensam suas atividades produtivas. Entender por que e como os homens agem e, quais são as influências operando sobre suas ações norteou o tema deste estudo. A proposta central desta tese foi compreender como fatores internos influenciam a tomada de decisão dos agricultores. Para tanto, observou-se os sistemas de produção de base ecológica da banana no Litoral Norte do RS. Nesse sentido, foram feitas cinquenta e três entrevistas, que compuseram uma amostra não probabilística, e os dados gerados foram analisados por meio de ferramentas de leitura de paisagem, estatística descritiva e análise multivariada. Os resultados sugerem que a paisagem da Microrregião do Litoral Norte do RS tem uma matriz formada por duas unidades geomorfológicas, a Serra Geral e a Planície Costeira, e que essas apresentam quatro unidades de paisagem distintas: Platô, Alta Encosta - Escarpa, Média e Baixa Encosta e Planície Aluvial e de Barreira. A paisagem Marca é baseada em elementos como banana, gado, produtos da cana de açúcar, extrativismo, arroz, e por se constituir em terras com restrições da legislação ambiental. Também gerou subsídios para o entendimento de que, na organização dos sistemas de produção, pelos agricultores, há uma importante influência de suas experiências pessoais e de valores mais ligados à satisfação. Em uma segunda etapa de tratamento dos dados foram gerados, por meio de uma análise de Cluster, seis grupos. E nesses observou-se que as decisões passam por um exame de elementos de disponibilidade dos meios de produção, como terra, capital e trabalho, os quais, de acordo com seu sistema de informação e orientação de valores, são organizados internamente em cada propriedade rural. É importante considerar que tais relações estão interligadas com seus objetivos, no intuito de projetar ações presentes e futuras, as quais relacionam-se com sua permanência na agricultura e em expectativa de sucessão. Destaca-se ainda, como contribuição, uma perspectiva de avanço nos estudos que têm se dedicado aos sistemas de produção com influência francofônica, visto que esse estudo destaca a importância de se considerar e incorporar efetivamente elementos do sistema social (sistema decisional familiar). Finalmente, observou-se que a construção elaborada por este trabalho, considerando os meios de produção, sistema de informação e o regime de valores, pode ser empregada em diferentes sistemas de produção. / The possibility of understanding how farmers live, what are their goals, political and economic conjunctures, values, beliefs and experiences in the space in which they live, all of these can help answering the question that is closely related to the way they organize and think about their productive activities. The theme of this thesis is founded on understanding why and how men act and what are the influences operating behind their actions. The main proposal of this thesis was to understand how internal factors influence the decision making process of farmers. In this sense, the focus was on the ecologically based production systems of bananas in the Northern Coast of the state of Rio Grande do Sul, Brazil. Therefore, a nonprobabilistic sample consisting of fifty-three interviews was created, and its corresponding data was analyzed by landscape reading tools, descriptive statistics and multivariate analysis. The results suggest that the landscape of the Northern Coast of Rio Grande do Sul has a matrix constituted by two geomorphological unities, the Serra Geral and the Planície Costeira, and that these unities present four distinct landscape unities: Platô, Alta Encosta – Escarpa, Média e Baixa Encosta e Planície Aluvial e de Barreira. The brand landscape is based on elements such as banana, cattle, sugar cane products, extrativism, rice, and by constituting itself on a land with environmental legislation restrictions. The results also generated contributions to the understanding that, in the organization of production systems, performed by farmers, there is an important influence of their personal experiences and values associated with satisfaction. In a second step of data treatment, six groups were generated by means of a cluster analysis. In these groups, it was observed that the decision pass through an examination of elements related to the availability of means of production such as land, capital and labor, which, according to their information system and value orientation, are organized internally in each rural property. It is important to consider that such relationships are intertwined with their goals, in order to project present and future actions, which are related to their stay in agriculture and their expectation of succession. It is also important to highlight as contribution, a perspective of progress in the Francophone influenced studies devoted to production systems, as this study highlights the importance of considering and effectively incorporating elements of the social system (familiar decisional system). Finally, it was observed that the construction that was developed in this work, considering the means of production, information systems and regime of values, could be employed in different production systems.

En esta tesis doctoral se estudia el modo de vida tritrófico del hongo nematófago Pochonia chlamydosporia utilizando técnicas "multiómicas". Pochonia chlamydosporia (= Metacordyceps chlamydosporia) (Goddard) Zare y Gams es un hongo nematófago usado para el control de nematodos agalladores de la raíz (Meloidogyne spp.) (Forghani and Hajihassani, 2020), entre otros. P. chlamydosporia se distribuye por todo el mundo y tiene un modo de vida tritrófico, pudiendo también adoptar estilos de vida endófito y saprófito. El mecanismo que utiliza P. clamydosporia para infectar huevos de nematodo comprende la desacetilación de la quitina de su pared celular a quitosano para facilitar su degradación por quitosanasas (Aranda-Martinez et al., 2016). El quitosano es un biopolímero derivado de la quitina que también se encuentra en el exoesqueleto de artrópodos y crustáceos. El genoma de P. chlamydosporia codifica un elevado número de quitosanasas, gracias a las cuales es resistente a quitosano y puede utilizarlo como fuente de nutrientes (Palma-Guerrero et al., 2010). Ambos pueden combinarse para el control de plagas. En este trabajo de tesis doctoral se pretende estudiar mediante metabolómica, transcriptómica y genómica el modo de vida tritrófico de P. chlamydosporia añadiendo quitosano, para determinar los mecanismos de interacción del hongo en ese entorno. En último término, se pretende sentar las bases para desarrollar un sistema para reducir plagas y enfermedades de forma sostenible.

Orientador: Roberto Lyra Villas Bôas / Banca: Sarita Leonel / Banca: Carlos Ruggiero / Banca : Ana Lúcia Borges / Banca: Victor Galan Saúco / Resumo: Objetivando avaliar os efeitos de doses de adubo orgânico na produção da bananeira 'Prata-Anã' durante cinco ciclos de produção, bem como estudar a liberação de nutrientes deste adubo aplicado ao solo e também a decomposição e liberação de nutrientes dos restos culturais, o presente trabalho foi conduzido na FCA/UNESP, em Botucatu-SP no período de novembro de 2002 a julho de 2007. A fonte de adubo orgânico foi mantida a mesma desde o primeiro ciclo, aplicando-se composto produzido a partir de serragem de madeira e esterco bovino, que constituíram os tratamentos (doses de composto orgânico): 0, 43, 86, 129 e 172 kg de composto por planta, o que correspondeu a 0; 98,5; 197,0; 290,5 e 394,0 g de K2O por planta, sendo estas doses calculadas de acordo com o teor de potássio presente no mesmo. No solo, a eficiência dos tratamentos foi avaliada mediante análises químicas de amostras de solo, enquanto que nas plantas avaliaram-se os teores de nutrientes presentes nas folhas, circunferência do pseudocaule, altura de inserção da inflorescência, número de folhas por planta, massa do cacho; número de frutos por cacho; número de pencas por cacho; peso da 2ª penca e número de frutos na 2ª penca. Também foram avaliados teores de nutrientes presentes em partes da plantas e a decomposição e liberação de nutrientes dos restos culturais. Para os frutos produzidos no 4º e 5º ciclos avaliaram-se a qualidade dos frutos por meio de análises físicas e químicas como textura, pH, acidez titulável, sólidos solúveis e amido da polpa. O delineamento experimental adotado foi em blocos casualizados, com cinco tratamentos, cinco repetições e duas plantas por parcela, sendo os dados submetidos à análise de variância e regressão. Diante das melhorias observadas no solo (manutenção do pH dentro de uma faixa adequada, elevação nos teores da matéria orgânica, do fósforo... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Aiming to evaluate the effects of organic compost rates in the production of banana plants 'Prata-Anã' in a five production cycle, as well as the nutrient liberation of this compost in the soil, the decomposition and nutrient liberation of the cultural residue, this present work was carried out at FCA/UNESP dependences, in Botucatu-SP from November of 2002 to July of 2007. The organic compost was the same produced since de first cycle, where it was applied compost produced by wood residue and bovine manure, which constituted the treatments (organic compost rates): 0, 43, 86, 129 and 172 kg of compost per plant, which corresponds to 0; 98,5; 197,0; 290,5 and 394,0 g of K2O per plant. These compost rates were calculated based on the quantity of potassium contained in the compost. The effects of organic fertilization in the soil were evaluated by chemical soil analyses. The efficiency of the treatment in plant development and production were evaluated by the quantity of nutrient present in the leaves, pseudostem circumference, plant height, number of leaves per plant, bunch weight, number of fruits in the bunch, number of hands per bunch, 2nd hand weight and number of fruits in the 2nd hand. It was also evaluated the nutrient levels in parts of the banana plants, decomposition and nutrient liberation of the cultural residues. Fruit quality produced in the 4th and 5th cycles was evaluated by physical and chemical analyses such as firmness, pH, acidity, soluble solids and starch. The experiment was arranged in randomized blocks design, with 5 treatments, 5 replications and 2 plants per plot. The obtained data were submitted to variance analyses and to regression analyses. The observed improvements in the soil (maintenance of the pH inside of an adjusted band, and the rises observed in the organic matter, phosphorus and calcium levels, as well as the addition of bases, capacity... (Complete abstract click electronic access below) / Doutor

L’objectif de cette thèse est de proposer une démarche pour identifier des plantes de service (Pds) utilisables en couverture vivante pour contrôler les adventices en bananeraie. Nous avons d’abord quantifié les effets de compétition réciproque entre le bananier et une couverture contrôlée par fauchage pour Brachiaria decumbens et Cynodon dactylon. Ces couverts ont eu des effets dépressifs sur la nutrition azotée du bananier et la productivité en premier cycle, le second cycle n’étant pas affecté. Dans un deuxième temps nous avons caractérisé au champ, en plantes isolées, la croissance en biomasse de huit légumineuses candidates sous différentes intensités lumineuses. En conditions lumineuses non limitantes, chaque espèce répondait à une dynamique exponentielle, définie par la biomasse 14 jours après semis et le taux de croissance relative (RGR). En conditions d’ombrage limitant, le RGR est réduit et le rapport surface foliaire sur biomasse aérienne croît. Ces réponses permettent de définir quatre stratégies d’adaptation à l’ombrage et d’identifier les Pds adaptées sous bananeraie. Pour trois de ces espèces, sur la base de la réponse de l’efficience photosynthétique, nous proposons un modèle de croissance en fonction de la ressource lumineuse. En peuplement, en présence d’adventices, aucune espèce évaluée n’a pu contrôler les grandes graminées, Stylosanthes guianensis et Centrosema pascuorum ont cependant réduit la biomasse des autres adventices de 60%. En bananeraie, les deux espèces évaluées ont exercé un contrôle sur les adventices mais ont réduit la productivité du premier cycle. Pour autant, ces résultats sont encourageants pour l’utilisation de Pds en bananeraie à des fins de contrôle des adventices. / The objective of this PhD thesis was to provide an approach to identify suitable cover crops (Pds) for weed control use in banana plantations. Firstly, we quantified the reciprocal effects between the banana crop and a grass cover controlled by mowing, for Brachiaria decumbens or Cynodon dactylon. These cover crops have had similar depressive effects on the nitrogen nutrition and on the productivity of the first cycle, but not afterward during the second cycle. Second step, we carried out a field characterization of eight legume cover crops, on isolated plants, under a range of light intensity. In non-limited light growth conditions, the biomass growth corresponded to an exponential dynamic, mathematically defined for each species by the biomass 14 days after sowing, and the relative growth rate (RGR). When affected by the shade, the RGR was reduced and the ratio between Leaf area and aerial plant biomass increased. We defined four adaptive strategies of the cover crops to the shade, what constitute criteria guidelines for cover crop use in banana cropping systems. For three of these species, on the basis of the response of the radiation use efficiency, we are proposing a plant growth model without any limiting factor other than light resource. In stands with the presence of weeds, neither of this cover crops was able to control the tall gramineous, but Stylosanthes guianensis and Centrosema pascuorum reduced the biomass of other weeds by 60%. Finally, in banana plantations, the two evaluated species provided a control of the weeds but reduced the productivity of the first cycle. Our results are comforting for the use of cover crops in banana plantation as a mean for weed control.

Incidental bycatch in gillnets is a substantial threat to small cetaceans. Using Acoustic Deterrent Devices, “pingers”, have successfully reduced bycatch of harbour porpoises in gillnets. However, seals can use pingers as “dinner-bells” to easier find gillnets in order to raid and destroy them, further aggravating the existing conflicts between seals and coastal fisheries. Therefore, in the present study, the efficiency of two alleged “seal-safe” pingers, an experimental Banana pinger “SSB” and a Future Oceans F70 pinger “FO”, in deterring harbour porpoises from the vicinity of gillnets and thereby reducing bycatch in commercial gillnet fisheries, was tested. This was done by deploying click detectors, “C-PODs”, recording Detection Positive Minutes per hour, at each end of gillnets, provided with the two pinger types or no pingers at all. Bycatch instances were recorded into logbooks by participating fishermen and verified using video footage from on-board video cameras. Results showed that video monitoring was a reliable method for verifying the number of bycatches of porpoises and seals, but not seabirds, recorded in the fishermen’s logbooks. The experimental SSB pingers and the FO pingers significantly reduced porpoise presence, measured as Detection Positive Minutes per hour in the vicinity of the nets, compared to gillnets without pingers. However, the sample size was too small to yield a significant result regarding the bycatch reducing efficiency and dinner bell effect of the experimental pingers. Nevertheless, bycatch trends suggest that pingers did in fact reduce porpoise bycatch. Although both successful, FO pingers were slightly more efficient in deterring porpoises than SSB pingers. The SSB pinger sounds had bigger directionality variations than the FO pinger, which may have affected its deterrent effects. Therefore, additional trials are needed to further investigate this aspect.

No description available.

Aux Antilles, dans les plantations de bananes en monoculture mécanisée, l'un des principaux problèmes à résoudre est le contrôle des populations de nématodes phytoparasites. Dans cette thèse, les effets d'apports de différentes matières organiques (MO), brutes ou compostées, sur la régulation biologique des nématodes ont été étudiés, cet effet suppresseur ayant déjà été montré sur d'autres cultures. L'analyse de la littérature sur le sujet montre que les effets d'un apport de MO sur les populations de nématodes phytoparasites et sur leurs dégâts sont complexes et varient fortement en fonction de la nature biochimique du produit et de l'espèce de nématode. Ainsi, les matières organiques qui libèrent beaucoup d'azote minéral en se décomposant favorisent la croissance des racines, ce qui peut augmenter la ressource alimentaire des nématodes phytoparasites et/ou la tolérance des plantes à leurs attaques. La décomposition des matières apportées peut libérer des composés nématotoxiques. Enfin, l'apport de carbone peut entrainer une diversification des communautés de nématodes, une complexification des réseaux trophiques et, par la suite, favoriser la régulation biologique des nématodes phytoparasites par les espèces appartenant aux niveaux trophiques supérieurs et par la microflore. Nous avons, par une étude fine de la structure des communautés de nématodes et le suivi de la croissance des jeunes plants de bananier, cherché à évaluer l'induction de la régulation biologique des nématodes parasites du bananier dans une sole bananière par un apport de MO, au moyen de deux expérimentations en pots conduites pendant 13 semaines. Les MO testées étaient quatre MO brutes et quatre MO compostées. L'expérience sur les MO brutes a montré que trois des quatre MO (bagasse, écumes de sucrerie et déchets verts) ont entrainé une diminution des populations de nématodes parasites dans les racines du bananier, l'intensité de cette régulation dépendant de l'espèce. En revanche, le quatrième type de MO, des boues de station d'épuration, n'a pas permis de diminuer la pression parasitaire. Les différences de croissance des systèmes racinaires n'ont pas été un facteur explicatif des régulations observées et les meilleures conditions de croissance observées n'ont pas réduit les impacts des nématodes phytoparasites sur les racines. Seules les écumes de sucrerie ont entrainé un impact positif global sur la plante, en diminuant la pression parasitaire tout en augmentant sa croissance. La bagasse et les déchets verts, principalement composés de lignines et de cellulose, ont entrainé une modification significative de la structure des communautés de nématodes, avec un fort accroissement des populations de nématodes fongivores et, avec la bagasse, de nématodes carnivores. L'expérience en pot sur les MO compostées a montré que les trois composts commerciaux produits par SITA VERDE (Biogwa, Ecogwa B, Ecogwa D) et l'amendement organique commercial Vegethumus (de Phallipou-Frayssinet) avaient engendré une diminution du parasitisme et que ce contrôle dépendait de l'espèce de nématodes phytoparasites. Dans cet essai, le contrôle des nématodes parasites du bananier est apparu lié à la biomasse racinaire totale des bananiers. L'apport des composts Ecogwa D et Vegethumus a augmenté la taille des populations de nématodes microbivores, mais seul Vegethumus a accru la voie de décomposition fongique. [...] Suite et fin du résumé dans la thèse. / In French West Indies, banana crops are generally managed as an intensive mechanized monoculture, and one of main problems to solve is the control of plant-parasitic nematodes. In this study, the effects of the input of different organic materials, gross or composted, on the biological control of nematodes were investigated. The analyze of the literature showed that the effects of an organic material input on plant-parasitic nematode populations and on their damage on the plant are complex and vary highly according to the biochemical characteristics of the products and the plant-parasitic nematode species. Thus, organic materials that release great amounts of mineral nitrogen during their decomposition promote root growth, which increases the feeding resource for plant-parasitic nematodes and/or plant tolerance to their attacks. Organic material decomposition can also release nematotoxic chemical compounds. Lastly, carbon input can lead to nematode community diversification, soil food web complexification, and, as a result, favoring the biological control of plant-parasitic nematodes by top predators or microflora. We evaluated the induction of the biological control of banana parasitic nematodes by an organic input, using soil nematofauna analyses and measuring the growth of young banana plants. We thus conducted two pot experimentations during 13 weeks. The organic materials tested were four raw and four composted organic materials that were locally available. The raw organic materials trial showed that three amongst the four amendments (sugarcane bagasse, sugarcane refinery sludge and plant residues) led to a decrease of parasitic nematode populations within banana roots, the control efficiency depending on nematode species. In contrast, the fourth type of organic material, sewage sludge, did not induce the decrease of the parasitic pressure. Changes in root growth were not an explanatory factor and the better soil conditions for plant growth did not reduce the impact of plant-parasitic nematode. Only sugarcane refinery sludge engendered overall positive effect on the banana plant, decreasing parasitic pressure and enhancing plant growth. Sugarcane bagasse and plant residues, mainly composed of lignins and cellulose, led to significant changes in nematode community structure, increasing fungivorous nematode populations and, only after bagasse supply, those of carnivorous nematodes. The compost trial showedndment that the three commercial composts produced by SITA Verde (Biogwa, Ecogwa B, Ecogwa D) and the commercial organic amendment Vegethumus (Phallipou-Frayssinet) induced a decrease of plant-parasitic nematode populations and that this control depended on banana parasitic nematode species. In this trial, the control of banana parasitic nematodes was linked to overall biomass of banana root system. The input of Ecogwa D and Vegethumus composts boosted microbivorous nematode populations, but only Vegethumus favored the fungal decomposition pathway. Last and final summary in the thesis.

>Magister Scientiae - MSc / An increasing number of measurements reveal the presence of a low-energy enhancement in the gamma-ray strength function (GSF). The GSF, which is the ability of nuclei to absorb or emit rays, provides insight into the statistical properties of atomic nuclei. For this project the GSF was studied for 74Ge which was populated in the reaction 74Ge(p,p')74Ge* at a beam energy of 18 MeV. The data were collected with the STARS-LIBERACE array at Lawrence Berkeley National Laboratory. Silicon detector telescopes were used for particle identi cation and rays in coincidence were detected with 5 clover-type high-purity germanium detectors. Through the analysis particle- - coincidence events were constructed. These events, together with well-known energy levels, were used to identify primary rays from the quasicontinuum. Primary rays from a broad excitation energy region, which decay to six 2+ states could be identi ed. These states and the associated primary rays are used to measure the GSF for 74Ge with the Ratio Method [1], which entails taking ratios of e ciency-corrected primary -ray intensities from the quasicontinuum. Results from the analysis of the data and focus on the existence of the low-energy enhancement in 74Ge will be discussed. The results are further discussed in the context of other work done on 74Ge using the ( , ') [2], (3He,3He') [3] and ( , ') [4] reactions.

Banana bunchy top virus (BBTV) causes one of the most devastating diseases of banana. Transgenic virus resistance is now considered one of the most promising strategies to control BBTV. Pathogen-derived resistance (PDR) strategies have been applied successfully to generate plants that are resistant to numerous different viruses, primarily against those viruses with RNA genomes. BBTV is a circular, single-stranded (css) DNA virus of the family Nanoviridae, which is closely related to the family Geminiviridae. Although there are some successful examples of PDR against geminiviruses, PDR against the nanoviruses has not been reported. Therefore, the aim of this thesis was to investigate the potential of BBTV genes to interfere with virus replication when used as transgenes for engineering banana plants resistance to BBTV. The replication initiation protein (Rep) of nanoviruses is the only viral protein essential for viral replication and represents an ideal target for PDR. Therefore, this thesis focused on the effect of wild-type or mutated Rep genes from BBTV satellite DNAs or the BBTV integral genome on the replication of BBTV in banana embryogenic cell suspensions. A new Rep-encoding satellite DNA, designated BBTV DNA-S4, was isolated from a Vietnamese BBTV isolate and characterised. When the effect of DNA-S4 on the replication of BBTV was examined, it was found that DNA-S4 enhanced the replication of BBTV. When the replicative capabilities of DNA-S4 and the previously characterised Rep-encoding BBTV satellite, DNA-S1, were compared, it was found that the amount of DNA-S4 accumulated to higher levels than DNA-S1. The interaction between BBTV and DNA-S1 was also examined. It was found that over-expression of the Rep encoded by DNA-S1 using ubi1 maize polyubiquitin promoter enhanced replication of BBTV. However, when the Rep-encoded by DNA-S1 was expressed by the native S1 promoter (in plasmid pBT1.1-S1), it suppressed the replication of BBTV. Based on this result, the use of DNA-S1 as a possible transgene to generate PDR against BBTV was investigated. The roles of the Rep-encoding and U5 genes of BBTV DNA-R, and the effects of over-expression of these two genes on BBTV replication were also investigated. Three mutants of BBTV DNA-R were constructed; plasmid pUbi-RepOnly-nos contained the ubi1 promoter driving Rep expression from DNA-R, plasmid pUbi-IntOnly-nos contained the ubi1 promoter driving expression of the DNA-R internal gene product (U5), while plasmid pUbi-R.ORF-nos contained the ubi1 promoter driving the expression of both Rep and the internal U5 gene product. The replication of BBTV was found to be significantly suppressed by pUbi-RepOnly-nos, weakly suppressed by pUbi-IntOnly-nos, but strongly enhanced by pUbi-R.ORF-nos. The effect of mutations in three conserved residues within the BBTV Rep on BBTV replication was also assessed. These mutations were all made in the regions in the ATPase motifs and resulted in changes from hydrophilic to hydrophobic residues (i.e. K187→M, D224→I and N268→L). None of these Rep mutants was able to initiate BBTV replication. However, over-expression of Reps containing the K187→M or N268→L mutations significantly suppressed the replication of BBTV. In summary, the Rep constructs that significantly suppressed replication of DNA-R and -C in banana embryogenic cell suspensions have the potential to confer resistance against BBTV by interfering with virus replication. It may be concluded that BBTV satellite DNAs are not ideal for conferring PDR because they did not suppress BBTV replication consistently. Wild-type Rep transcripts and mutated (i.e. K187→M and N248→L) Rep proteins of BBTV DNA-R, however, when over-expressed by a strong promoter, are all promising candidates for generating BBTV-resistant banana plants.