The objective of this work was to evaluate the influence of the fruit maturation stage in the physical attributes and germination of Schefflera morototoni pyrenes subjected to pre-germination treatments. Fruits with green and purplish green coloration were collected from 14 individuals, pulped in running water, the hollow pyrenes were discarded after counting, together with those presenting retracted and oxidized endosperm, using the uniforms (with the greenish endosperm occupying the whole cavity of the pyrene). The experiment was conducted in completely randomized design in a 2 x 5 factorial (stages of fruit maturation and pre-germination treatments), with four repetitions in plots containing 25 pyrenes. For greater capacity and germination speed of the pyrenes, fruits should be harvested when they present a purplish green coloration, discarding those with hollow pyrenes, with retracted or oxidized endosperm. The germination capacity of the pyrenes with uniform endosperm varied between 50 and 60%, with the beginning of the process at about 40 days after sowing and extending for up to 60 days in vermiculite. Pulped pyrenes, dried and soaked in water at 60ºC for 5 minutes, followed by soaking in water at room temperature for 12 hours begin the germination process in less time, in relation to those pulped, dried, scarified and soaked for 6 hours. The fruit endocarp is permeable and rigid; however, it presents a natural opening when soaked. The objective was to evaluate the variability in seedling emergence measures of Schefflera morototoni from pyrenes of different individuals. Fruits of 14 individuals were pulped and pyrenes with uniform endosperm were selected. The experiment was conducted in completely randomized design with 14 treatments (individuals) and 11 repetitions in parcels containing 50 pyrenes with uniform endosperm treated by immersion in water at 60 ºC for 5 minutes and then soaked at room temperature for 12 hours. The substrate used was a mixture in proportion 2:1:1:1/2 (v/v) soil, commercial substrate Bioplant®, coarse sand and vermicompost, with pyrenes sown at 1 cm depth in expanded polystyrene trays, maintained in a nursery with 50% reduction in luminosity at average temperatures of 19.3ºC minimum and 30.2 ºC maximum and daily irrigation. Daily counting of seedlings evaluated capacity, time, rate, uniformity and synchrony of emergence, besides the distribution of frequency of emergence in relation to time. The emergence of seedlings is slow, irregular and asynchronous, taking more than 80 days for stabilization of the emergence. The percentage of seedlings can reach up to 57%, but even when the endosperm occupies the whole cavity of the pyrene and is greenish, the emergence of seedlings may not occur. There is variability in seedling emergence measurements from pyrenes of different Schefflera morototoni individuals. / CAPÍTULO II: O objetivo do trabalho foi avaliar a influência do estádio de maturação dos frutos nos atributos físicos e de germinação de pirênios de Schefflera morototoni submetidos a tratamentos pré-germinativos. Frutos com coloração verde e verde-arroxeada foram coletados de 14 indivíduos, despolpados em água corrente, descartando-se, após contabilização, os pirênios chochos, com endosperma retraído e oxidado, utilizando-se os uniformes (com endosperma esverdeado ocupando toda a cavidade do pirênio). O delineamento experimental foi o inteiramente casualizado em esquema fatorial 2 x 5 (estádios de maturação dos frutos e tratamentos pré-germinativos), com quatro repetições em parcelas contendo 25 pirênios. Verificou-se que para maior capacidade e velocidade de germinação dos pirênios, os frutos devem ser colhidos quando apresentarem coloração verde-arroxeada, descartando-se àqueles com pirênios chochos, endosperma retraído ou oxidado. A capacidade de germinação dos pirênios com endosperma uniforme varia entre 50 e 60%, com início do processo em cerca de 40 dias após semeadura, se estendendo por até 60 dias em vermiculita. Pirênios despolpados, secos e embebidos em água a 60oC por 5 minutos, seguida da embebição em água à temperatura ambiente por 12 horas iniciam o processo de germinação em menor tempo, em relação aos despolpados, secos, escarificados e embebidos por 6 horas. O endocarpo dos frutos é permeável e rígido, no entanto, apresenta abertura natural quando embebido. CAPÍTULO III: O objetivo foi avaliar a variabilidade nas medidas de emergência de plântulas de Schefflera morototoni provenientes de pirênios de diferentes indivíduos. Frutos de 14 indivíduos foram despolpados, selecionando-se pirênios com endosperma uniforme. O experimento de emergência foi conduzido em delineamento inteiramente casualizado com 14 tratamentos (indivíduos) e 11 repetições em parcelas contendo 50 pirênios com endosperma uniforme imersos em água a 60 ºC por 5 minutos e posteriormente embebidos em água destilada à temperatura ambiente por 12 horas. O substrato utilizado foi uma mistura na proporção 2:1:1:1/2 (v/v) de solo, substrato comercial Bioplant®, areia de textura grossa e vermicomposto, com pirênios semeados a 1 cm de profundidade em bandejas de poliestireno expandido, mantidas em viveiro com sombrite de 50% de redução luminosa e médias de temperaturas de 19,3 ºC a mínima e 30,2 ºC a máxima e irrigadas diariamente. Das contagens diárias das plântulas emergidas foram avaliadas medidas de capacidade, tempo, velocidade, uniformidade e sincronia de emergência, além da distribuição de frequência percentual de emergência em relação ao tempo. A emergência das plântulas é tardia, irregular e assíncrona, gastando mais de 80 dias para estabilização do estande. A porcentagem de plântulas emergidas pode atingir até 57%, porém mesmo quando o endosperma ocupa toda a cavidade do pirênio e está esverdeado, a emergência das plântulas pode não ocorrer. Há variabilidade nas medidas de emergência de plântulas quando obtidas de pirênios de indivíduos distintos de Schefflera morototoni. / Mestre em Agronomia

I denna fallstudie har SeventyOne Consulting analyserats som ett exempel på en organisation som verkar under det kommande paradigmet inom kvalitetsutvecklingen. Studien kopplar samman teori från kvalitetfältet med design thinking, paradigmteori och teori om människocentrerad företagskultur. Syftet var att bidra med kunskap gällande vilken roll design thinking och människocentrerad företagskultur kan spela i ett kommande paradigm inom kvalitetsutveckling. Frågeställningarna var: 1. Hur kan det kommande paradigmet i kvalitetsutveckling förstås? 2. Vilken roll kan design thinking och en människocentrerad företagskultur spela i det kommande paradigmet? Metoden inkluderade semi-deltagande observationer av organisationen, icke-deltagande observationer av arbetet med kunder, intervjuer med företagets medlemmar samt dokumentationsanalys. Studien har huvudsakligen genomförts online. Dess resultat har organiserats i den metaforiska och hypotetiska analysmodellen bröllopstårtan, vilken illustrerar hur en människocentrerad företagskultur baserad på psykologisk trygghet, Teal-principer och glädje utgör grunden för att hantera kunders komplexa problem utifrån de metodologiska strategierna relatera och samskapa, eklektisk metod och ett design thinking mindset. Design kapabilitet har analyserats som förmågan att sammankoppla och arbeta utifrån flera olika kunskapstraditioner samtidigt, samt integrera företagskulturer utifrån en människocentrerad bas. Människocentrerad kultur har därmed förståtts som en förutsättning för att kunna möta komplexiteten och innovationskraven som präglar det nya paradigmet, medan design thinking förståtts som en potentiellt användbar metod, förutsatt att design kapabilitet utvecklats. / In this case study, SeventyOne Consulting was analysed as an example of an organisation operating under the coming paradigm in quality management. The study connected theory from quality management, design thinking, paradigm theory and human-centred culture theory. The purpose was to contribute with knowledge concerning what role design thinking and a human-centred culture can play in the coming paradigm of quality management. The research questions were: 1. How can the coming paradigm of Quality Management be understood? 2. Which roles can design thinking and a human-centred culture play in the coming paradigm? The method included semi-participatory observations of the organisation, non-participatory observations with its customers, interviews with its members and document analysis. The study has mainly been performed online. Its result were organised into the metaphorical and hypothetical analytic model of the wedding cake, illustrating how a human-centred culture based on psychological safety, Teal principles and happiness gives the foundation for handling customers’ complex problems through the methodological strategies relate and co-create, eclectic methodology and a design thinking mindset. Design capability was analysed as the ability to connect and work simultaneously with different kinds of knowledge and integrating cultures, while also coming from a human-centredness. Human-centred cultures were thereby understood as an important prerequisite for being able to meet the complexity and innovative demands of a new paradigm, while design thinking was understood as a potentially suitable method, provided that design-capability has been developed. / <p>2021-06-06</p>

Final thesis titled Collective Intelligence and the Functions of Individual: Using an Example of Social Activism Online uses definition of collective intelligence by Pierre Lévy, and tries to verify it throught practice of social activism on the internet using a smartphone as a tool for accessing cyberspace. The theses is based on media theory works focusing in particular on a new kind of intelligence of community and the impact of new communication technologies on humans. Next part is about the topics of social activism, when considering together or independently with collective intelligence, provides the potential for direct democracy. Lastly there are few examples of social activism online or forerunners of direct democracy. As an important issue of collective intelligence in practice emerge the rules of behavior of individuals and Lévy's vision of collective intelligence as a peak of humanity.

Doctor of Philosophy / Department of Agronomy / Johanna A. Dille / Challenges in weed management include occurrence of multiple weed species in the field, variable emergence among weed species, different spatial distribution and weed densities, which leads to the persistence of weed patches. The overall objective of this research was to understand the interaction of weed emergence, weed density, herbicide choice, and herbicide rate in soybean. Specific objectives were 1) to characterize the seedbank and emergence patterns of shattercane (Sorghum bicolor L.), prickly sida (Sida spinosa L.), and ivyleaf morningglory (Ipomoea hederacea Jacq.) including initial, peak, end, and duration of emergence in response to crop and herbicide treatments in soybean, and 2) to evaluate large crabgrass (Digitaria sanguinalis L.), shattercane, Palmer amaranth (Amaranthus palmeri S.), and velvetleaf (Abutilon theophrasti Medik.) mortality and dry weight reduction in response to herbicide rates across varying weed densities as well as to determine the influence of velvetleaf growth stage and density on herbicide efficacy. In the emergence study of 2006 to 2008, four treatments were nocrop, no-residual herbicide, half-rate of residual herbicide and full-rate of residual herbicide. Reduction in weed emergence was observed over the years in the same species patch. Species emerged in mid-May in both years, coinciding with soybean planting. Extended emergence was observed for shattercane when moisture was low and temperature high, while for prickly sida and ivyleaf morningglory, extended emergence was observed when moisture was high and temperature low. Applying residual herbicide decreased weed emergence. Herbicide choice was the whole plot, herbicide rates were subplots and weed densities were sub-subplots in field experiments conducted in 2006 and 2007. Shattercane was more susceptible to both glyphosate and clethodim than large crabgrass. Increasing large crabgrass density reduced percent mortality with clethodim, while with glyphosate, density did not affect both species mortality. Shattercane dry weight was reduced to 0 g per plot with 0.1X labeled rate of clethodim or glyphosate while 0.5X of the labeled rate reduced dry weight of large crabgrass to 0 g per plot. For broadleaf weeds, higher percent mortality was observed with glyphosate than with lactofen at high densities. Palmer amaranth was more susceptible than velvetleaf. Velvetleaf response was density dependent, such that increasing density did not increase dry weight. Velvetleaf growth stage was of importance, as stage affected herbicide efficacy, with higher mortality achieved at the two-leaf stage than the four- and six-leaf stages. For glyphosate, 0.125X of labeled rate on velvetleaf density of 5 seedlings per pot achieved more than 90% mortality when applied at the two-leaf stage, but dropped to 60 and 50% mortality when applied at the four- and six-leaf stage, respectively. The trend was the same for velvetleaf at a density of 30 seedlings per pot, which had 80, 60, and 55% mortality for the two-, four-, and six-leaf stages, respectively. Weed managers and farmers have the opportunity to better select herbicide choice and rate based on weed species, weed emergence patterns, and weed density.

Thesis (MA(VA))--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This thesis entails a practice-led theoretical discussion on generative art production within an ecological framework. It is based on my work in Eyemvelo Kosbos (2010- ), an interdisciplinary collaborative project geared toward food production within ecologically sound parameters. Acting in my capacity as live-in curator of this agroecological space, I have subsequently formulated a series of biological generative artworks known as Ecological Concept Objects (2011- ), which serve as the main practical component of this research. By establishing philosophical realism as the main theoretical premise, I formulate an understanding of my art practice as a collaboration with the world. Core philosophical sources such as Graham Harman, Bruno Latour and Manuel DeLanda are cited to elucidate the theoretical underpinnings of my work. A case is made for aesthetics to be understood in its classical sense – as a discourse of sense perception, as opposed to visual taste or beauty. By discussing relevant examples from contemporary generative art, along with the theoretical insights of many practicing artists, key concepts such as emergence and self-organisation are identified as pivotal to generative practice. A definitive understanding of generative art is fomented whereby the artist willingly relinquishes creative agency and decision-making to impersonal forces. An historical context is provided which shows a precedent for similar art practices. The world is accordingly posited to be a vast interdependent network of real autonomous entities coming into relations with other real autonomous entities. This conception furthermore challenges a mutually-exclusive dichotomy of ‘Nature’ and culture, by suggesting that these two supposed binaries are so entangled that any separation thereof is a blatant form of idealism, if indeed ‘Nature’ can even be said to exist at all. An integrated ecological practice is nonetheless encouraged throughout as a central theme or primary conceptual parameter for both this dissertation and its accompanying practical body of work. Permaculture, a systems-based design science geared towards sustainability, is identified and adopted as a working example of an ecological practice which consolidates ‘human care’ with ‘earth care’, as the latter naturally encompasses the former. The goal of this research is then to investigate a practice where the artist, despite being restricted to linear action in the world, works in such a way as to allow the non-linear dynamics of emergent potential to reveal itself on its own terms. Such a methodology stands in stark contrast to an anthropocentric mastery of predictable matter, where little provision is made for anomalies, accidents or emergent forms. Generative art, on the other hand, is shown to make such provisions as it affords self-organisation to its medium, as entities are given time and space to express themselves in unique assemblages. / AFRIKAANSE OPSOMMING: Hierdie tesis behels 'n praktyk-geleide teoretiese bespreking oor generatiewe kunsproduksie binne 'n wyer ekologiese raamwerk. Dit is gebaseer op my werk in Eyemvelo Kosbos (2010 - ), 'n interdissiplinêre gesamentlike projek wat daarop gemik is om voedsel binne ekologies verantwoordelike perke te produseer. In my hoedanigheid as inwonende kurator van hierdie agri-ekologiese projek, het ek 'n reeks biologiese generatiewe kunswerke geformuleer wat bekend staan as Ecological Concept Objects (2011- ), wat dien as die primêre praktiese komponent van hierdie navorsing. Met die vestiging van filosofiese realisme as die kern teoretiese uitgangspunt, formuleer ek 'n begrip van my kunspraktyk as 'n ‘samewerking met die wêreld.’ Die teoretiese fondasies van my werk word uitgelig deur verwysing te maak na kern filosofiese bronne soos Graham Harman, Bruno Latour en Manuel DeLanda, onder andere. 'n Argument word geformuleer waarvolgens die term estetika in sy klassieke sin verstaan moet word - as 'n diskoers oor sintuiglike persepsie, in teenstelling tot ‘n bespreking oor visuele smaak of skoonheid. Sleutelkonsepte soos opkoms (emergence) en self-organisasie word geïdentifiseer as deurslaggewend vir ‘n sinvolle bespreking van generatiewe praktyke. By die bespreking van relevante voorbeelde van kontemporêre generatiewe kuns, saam met die teoretiese insigte van verskeie praktiserende kunstenaars, word 'n werkende begrip van generatiewe kuns ontwikkel waarvolgens die kunstenaar kreatiewe agentskap en besluitneming vrywillig afstaan aan onpersoonlike kragte. 'n Historiese konteks word verder verskaf wat 'n presedent aandui vir soortgelyke kunspraktyke. Die wêreld word dan daarvolgens geposisioneer as 'n groot netwerk van werklike outonome entiteite wat verhoudings met ander werklike outonome entiteite aanknoop. Hierdie opvatting daag verder 'n wedersyds-eksklusiewe dualisme van 'Natuur' en kultuur uit, deur voor te stel dat hierdie twee veronderstelde binêre teenstrydighede sό verstrengel is dat enige skeiding daarvan inderdaad voorkom as 'n blatante vorm van idealisme. 'n Geïntegreerde ekologiese praktyk word egter aangemoedig om deurgaans as 'n sentrale tema of primêre konseptuele riglyn vir beide hierdie tesis en die gepaardgaande praktiese werk te dien. Permaculture, 'n stelsels-georiënteerde ontwerpwetenskap gerig op volhoubaarheid, word geïdentifiseer en aanvaar as 'n werkende voorbeeld van 'n ekologiese praktyk wat ‘sorg van mense’ met 'sorg van die planeet" vereenselwig, aangesien laasgenoemde daarvolgens die eersgenoemde insluit . Derhalwe, is die doel van hierdie navorsing om ondersoek in te stel tot 'n praktyk waar die kunstenaar, ten spyte daarvan dat sy beperk is tot lineêre aksie, in so 'n manier te werk gaan dat die nie-lineêre dinamika van ontluikende potensiaal geopenbaar kan word. So 'n metode staan in kontras met 'n eenrigting antroposentriese bemeestering van voorspelbare materie - waar daar min voorsiening vir ongerymdhede, ongelukke of ontluikende vorms gemaak word. Daar word egter bevind dat generatiewe kunspraktyk wel hierdie voorsienings maak, aangesien dit self-organisasie aan die medium toe staan, sodat entiteite tyd en ruimte verskaf kan word om hulself uit te druk in unieke samestellings.

Le Rice yellow mottle virus (RYMV) est un virus émergeant qui constitue actuellement une contrainte majeure à la riziculture sur le continent africain. Quelques rares variétés de riz, issues des espèces cultivées de riz africain et asiatique (respectivement Oryza glaberrima et O. sativa), ont récemment été identifiées comme hautement résistantes au RYMV. Ce phénotype de résistance est dû à un gène récessif RYMV1 codant le facteur d'initiation de la traduction eIF(iso)4G1 du riz.Les objectifs de cette thèse sont (i) d'étudier la durabilité de la résistance élevée du riz contre le RYMV avant son déploiement à large échelle, (ii) de caractériser les mécanismes d'émergence de génotypes contournants et (iii) d'identifier des signatures moléculaires influençant ces processus d'adaptation. Ainsi, le contournement de deux allèles de résistance, identifiés chez les deux espèces de riz cultivés, a été relié à l'émergence de mutations dans la protéine virale VPg qui permettent de rétablir l'interaction avec le facteur eIF(iso)4G1 de l'hôte résistant. Un site sous sélection diversificatrice de la VPg influence directement la capacité de contournement de la résistance élevée en fonction de l'espèce hôte. Ce site, proche des mutations de contournement, est impliqué dans l'adaptation du virus à l'espèce O. glaberrima au cours de son histoire évolutive. La démarche employée au cours de ce travail combine des études d'évolution expérimentale à des analyses fonctionnelles. Les résultats obtenus par cette approche intégrative participeront à la mise en place de stratégies de lutte intégrée à la fois efficaces et durables face à la maladie de la panachure jaune du riz en Afrique. / The Rice yellow mottle virus (RYMV) is an emerging virus currently considered as the major constraint to rice production in Africa. Some varieties of African and Asian cultivated rice (Oryza glaberrima and O. sativa, respectively), have recently been identified as highly resistant to RYMV. This resistance phenotype is caused by a recessive gene RYMV1 encoding the translation initiation factor eIF(iso)4G1 of rice.The objectives of this thesis are (i) to investigate the durability of the high resistance of rice against RYMV before broadly deployment in fields, (ii) to characterize the mechanisms of emergence of resistance-breaking (RB) genotypes and (iii) to identify molecular signatures that influence these processes of adaptation. The resistance-breaking of two resistance alleles, identified in both cultivated rice species, is mainly associated with the emergence of mutations in the viral protein VPg that restore in resistant hosts the interaction with the factor eIF(iso)4G1. A site of VPg under diversifying selection directly affects the ability to overcome the high resistance depending on the host species. This site, near the RB mutations, is involved in the adaptation of the RYMV to O. glaberrima species during its evolutionary history. The approach used during this work combines experimental evolution and functional analyses. The results of this integrative study will participate in the development of effective and sustainable control strategies toward the Rice yellow mottle virus in Africa.

In this research, a multi-agent system called KMAS is presented that models an environment of intelligent, autonomous, rational, and adaptive agents that reason about trust, and adapt trust based on experience. Agents reason and adapt using a modification of the k-Nearest Neighbor algorithm called (k X n) Nearest Neighbor where k neighbors recommend reputation values for trust during each of n interactions. Reputation allows a single agent to receive recommendations about the trustworthiness of others. One goal is to present a recommendation model of trust that outperforms MAS architectures relying solely on direct agent interaction. A second goal is to converge KMAS to an emergent system state where only successful cooperation is allowed. Three experiments are chosen to compare KMAS against a non-(k X n) MAS, and between different variations of KMAS execution. Research results show KMAS converges to the desired state, and in the context of this research, KMAS outperforms a direct interaction-based system.

The ubiquity of digital media provides an unprecedented possibility to redefine the process and methods of design. Through experience from a series of creative projects, I investigate how certain aspects of the web allow for design to attain a degree of autonomy, thus producing results that go beyond anticipation and expertise of the author. Utilizing an unlimited capacity to store the content and retrieve immediate feedback, the designer’s role can be shifted to that of an initiator defining rules and boundaries, from which the process can evolve independently based on the input of users and data. The design output in such conditions is the development of schemes in which the author remains, but is marginalized as a producer – consciously restraining his level of control. Rather then struggling to add something singular to the bottomless pit of information, the designer is relegated in the role of medium: collecting and recombining the bits of fragmented data into the structures conveying meaning.

La compréhension du processus d’adaptation des populations de parasites à leur plante-hôte est une question fondamentale en écologie évolutive. C’est également un enjeu majeur de recherche finalisée qui a des retombées pour la protection des cultures. L’oomycète Plasmopara viticola, agent causal du mildiou de la vigne, attaque les espèces du genre Vitis. Dans un contexte où l’enjeu principal des programmes d’amélioration est la durabilité des résistances, des connaissances nouvelles sur l’écologie et l’évolution de l'interaction entre le parasite et son hôte sont nécessaires afin d’évaluer le potentiel du mildiou à surmonter ces résistances. Dans ma thèse, je me suis intéressée au rôle de la plante-hôte comme facteur d’évolution des populations de mildiou, en posant cette question à différentes échelles évolutives : (i) dans le bassin d’origine du pathogène (Amérique du Nord), j’ai cherché à évaluer le degré de spécialisation du parasite sur sa gamme d’hôtes sauvages et cultivés; (ii) en Europe, où le mildiou de la vigne a été introduit récemment, j’ai étudié l’évolution des populations de mildiou soumis à la pression de sélection des résistances des nouvelles variétés de vigne. Pour comprendre la spécialisation plante-hôte dans ce pathosystème où plusieurs espèces cryptiques ont été identifiées, nous avons réalisé des tests d’inoculations croisées entre espèces hôtes (Vitis spp.) et agent pathogène (P. viticola). Les données phénotypiques et morphologiques apportent les preuves d’une spécialisation plante-hôte au sein des populations de P. viticola : les espèces A et D de mildiou sont spécialisées sur leur plante-hôte, tandis que le processus de spécialisation est en cours pour les espèces B et C. Même si aucune différenciation génétique n’a été montrée au sein de l’espèce C, il existe deux groupes distincts au sein de l’espèce B. Les isolats du compartiment cultivé sont en moyenne plus agressifs que les isolats issus des vignes sauvages, indiquant une adaptation des isolats cultivés sur leur plante hôte. A partir d’un large échantillonnage, nous avons étudié la distribution des espèces de mildiou sur leurs plantes-hôtes sauvages et cultivées. Ce travail a permis d’identifier une nouvelle espèce cryptique et a confirmé la spécialisation plante-hôte. En Europe, nos résultats montrent que le déploiement limité de variétés à résistantes partielles a conduit à des modifications des populations de mildiou: apparition d’isolats virulents (i.e. contournant un QTL majeur de résistance), et augmentation de l’agressivité sur Vitis vinifera. Dans le but de comprendre les mécanismes à l’origine de la spécialisation et du contournement des résistances, nous nous sommes intéressés au répertoire d’effecteurs du parasite. Une centaine d’effecteurs candidats ont été identifiés en utilisant les données disponibles sur le génome de P. viticola. L’analyse du polymorphisme de 32 candidats sur une sélection d’isolats montre que trois d’entre eux évoluent sous sélection positive. Ces résultats soulignent l’importance de la plante-hôte comme facteur de diversification des populations de l’agent pathogène et révèlent que le mildiou s’adapte rapidement aux résistances de la vigne. Il est désormais nécessaire de mieux appréhender le déploiement des résistances de la vigne afin qu’elles puissent être durables. / Understanding the process of adaptation of parasite populations to their host-plant is a key issue in evolutionary ecology. It is also a major subject in applied research that has implications for crop protection. The oomycete Plasmopara viticola, the causal agent of downy mildew, attacks the species of the Vitis genus. In a context where the main concern of the breeding programs is the durability of resistance, new knowledge about the ecology and evolution of the interaction between parasite and host is needed in order to evaluate the potential of downy mildew to overcome the resistance. In my thesis, I addressed the role of the host-plant as an evolutionary factor for downy mildew populations, by asking this question at two different evolutionary scales: (i) in the pathogen region of origin (North America) I assessed the degree of specialization of the parasite on its wild and cultivated host range (ii) in Europe, where downy mildew has been introduced recently, I studied the evolution of downy mildew populations subject to the selection pressure imposed by resistant grapevine varieties. To understand the host-plant specialization in this pathosystem, where several cryptic species have been identified, we performed cross inoculations between different host (Vitis spp.) and pathogen (P. viticola) species. Morphological and phenotypic data provide evidence of host-plant specialization in P. viticola populations: downy mildew species A and D are specialized on their host-plant, while the specialization process is ongoing for species B and C. Although no genetic differentiation has been shown inside species C, there are two distinct groups within species B. Isolates from the cultivated compartment are on average more aggressive than isolates from wild vines, indicating an adaptation of isolates growing on cultivated host-plants. Finally, a large-scale study of the distribution of downy mildew species on both their wild and cultivated host-plants resulted in the identification of a new cryptic species and confirmed the host-plant specialization. In Europe, our results show that the limited deployment of resistant varieties has led to changes in downy mildew populations: emergence of virulent isolates (i.e. breakdown of a major QTL for resistance), and increased aggressiveness on Vitis vinifera. In order to understand the mechanisms at the origin of specialization and resistance breakdown, we examined the parasite’s effector repertoire. Over one hundred effector candidates were identified using available data on the P. viticola genome. The polymorphism of 32 candidate genes revealed that three of them evolve under positive selection. Our results reveal the strong ability of downy mildew to adapt to its host plant and to plant resistance. They should be taken into account when devising strategies for the deployment of grapevine resistances in order to guarantee their durability.

Master of Science / Department of Biology / Samantha M. Wisely / Nearly 30% of emerging infectious diseases are caused by vector-borne pathogens with wildlife origins, posing a risk for public health, livestock, and wildlife species of conservation concern. Understanding the spatial patterns of exposure to dipteran vectors and their associated pathogens is critical for epidemiological research to target prevention and control of vector-borne infectious diseases. In recent years, Western Equine encephalitis, St. Louis encephalitis, West Nile Virus encephalitis and avian malaria have not only been a public health concern but also a conservation concern, specifically the conservation of grassland nesting birds. Although the central Great Plains is the most specious region for grassland nesting birds, their role in the enzootic (primary) amplification cycle of infectious diseases may lead to further population depressions, and could potentially result in spill-over events to humans and livestock. The goals of my thesis were 1) to identify the underlying causes of spatio-temporal abundance patterns of mosquito vectors within the grasslands of the eastern Smoky Hills, and 2) to create probabilistic distributions of functional disease vectors, to evaluate disease risk in Greater Prairie-chicken (Tympanuchus cupido, surrogate species for other grassland nesting birds). First, I found that temporal dynamics in mosquito abundances were explained by maximum and minimum temperature indices. Spatial dynamics in mosquito abundances were best explained by environmental variables, such as curvature, TWI (Topographic Wetness Index), distance to woodland and distance to road. Second, the overall predictive power of the ecological niche models of important vector species in the grasslands of the Smoky Hills was better than random predictions, indicating that the most important predictor variables in their distribution were: distance to water, TWI, AASHTO (soil particle size distribution), and mean temperature during the coldest quarter. Furthermore, the spatial analysis indicated that Greater Prairie-chicken nest in areas with a higher probability of vector occurrence than other potentially available habitats within the grasslands. However, I failed to detect a significant difference in the probability of vector occurrence at nest of infected versus uninfected females. Understanding the distribution and abundance patterns of vectors of infectious diseases can provide important insights for wildlife conservation as well as public health management.