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.

No description available.

Grapevine (Vitis spp.) is one of the most widely cultivated perennial fruit crops in the world and its economic relevance is mainly related to wine production. In recent years, the increased frequency of extreme phenomena such as heat waves has been acknowledged as one of the most significant climate variables negatively affecting grape yield and berry composition, with consequences also on wine quality. Thus, studying the physiological, metabolic and genetic factors that are involved in grapevine response to high temperatures is essential to improve the knowledge of mechanisms underlying thermotolerance, aiming to support plant breeding innovation and the development of new management strategies in viticulture. In this work, a segregating population obtained from the crossing of ‘Rhine Riesling’ and ‘Cabernet Sauvignon’ was studied in the field with a multidisciplinary approach. The progeny (around 120 genotypes) was evaluated for phenological traits affected by changing temperatures, in particular bud burst, flowering and véraison, while physiological response to heat stress was assessed in various hot summer days by measuring chlorophyll fluorescence kinetics and stomatal conductance. Measures were collected in the early morning as control and in the afternoon during hot hours. Phenotypic data were then used in combination with a high-density linkage map (average distance between adjacent markers 0.78 cM), previously developed using genotypic information from 139 individuals, to perform QTL analysis. Based on physiological responses to high temperatures, selected individuals showing contrasting behaviour, together with parental lines, were further studied in controlled conditions. In the field, in fact, plants may be subjected to combined stresses and changes in environmental conditions may heavily influence plants response. With the experiment in controlled condition, on the other hand, plants were stressed at higher temperatures, compared to the ones registered in the field, by maintaining all the other sources of variability constant. In the growth chamber plants were studied for their physiological response to heat stress by using the same approach adopted in the field. To better understand mechanisms involved in grapevine adaptation to heat stress conditions, individuals with contrasting behaviour were studied also for their metabolome modifications, both in the field and in controlled conditions. Volatile organic compounds (VOCs) were investigated with an untargeted approach applying conventional methods of analysis. Accumulation of VOCs in grapevine leaves was analysed using gas chromatography coupled with mass spectrometry (GC-MS) after a pre-concentration with a solid-phase micro-extraction (SPME) approach. On the other hand, VOCs emission during stress was investigated in controlled conditions thanks to the use of the Closed-Loop Stripping Analysis (CLSA) which allows the collection of VOCs directly emitted by plants. Analysis was then performed with GC-MS. Metabolic alterations of non-volatile compounds were examined with an untargeted analysis using high-performance liquid chromatography coupled with a high-resolution mass spectrometer equipped with an electrospray soft ionization (HPLC-HR-ESI-MS). In this work a metabolomic workflow was developed, starting from sample collection and extraction to sample analysis and data interpretation. The analytical method developed allowed the preliminary evaluation of leaf metabolome alterations due to stress factors. In fact, the use of a weak cation-exchange mixed mode column, in combination with a data dependent acquisition mode, allowed a first wide screening of both primary and secondary metabolites resulting in a good compromise for metabolic fingerprinting. QTL analysis on the segregating population allowed the identification of several QTLs, related to both phenological and physiological traits, with the discovery of interesting putative candidate genes for grapevine resilience to changing temperatures. This is the first time that a similar approach has been applied to a perennial fruit crop by analysing chlorophyll fluorescence and leaf transpiration traits related to heat stress. On the other hand, the multidisciplinary approach allowed the fine characterization of Rhine Riesling and Cabernet Sauvignon response to high temperatures, both in controlled and field conditions, a tentative classification of ‘tolerant’ and ‘susceptible’ progeny individuals and the identification of metabolic pathways altered during heat stress in the susceptible plants. Together with the implementation of a novel metabolomic workflow based on HPLC-HR-ESI-MS, this work represents a novelty in studies on grapevine response to changing temperatures, as it considered not only the berry metabolism but the resilience of the plants itself, paving the way for future studies on thermotolerance.

Les traits d’insensibilité émotionnelle (TIÉ) sont définis comme une constellation de caractéristiques incluant des affects superficiels, le manque de remords et de culpabilité et une réponse empathique réduite aux états affectifs d’autrui. En effet, des associations négatives ont été identifiées entre les TIÉ et différentes formes d’empathie, soit l’empathie motrice, l’empathie affective, et l’empathie cognitive. La plupart des travaux dans ce domaine ont porté sur des échantillons de garçons, de sorte que les connaissances sur le sujet auprès des filles sont limitées. En outre, l’hétérogénéité des personnes ayant des TIÉ n’a pas toujours été considérée dans les travaux antérieurs. L’anxiété a toutefois été proposée comme une caractéristique permettant de distinguer deux variantes des TIÉ, l’une caractérisée par un niveau élevé d’anxiété et l’autre par un niveau faible d’anxiété. Dans cette étude, nous visons à examiner les associations entre les TIÉ et différentes formes d’empathie (motrice, affective et cognitive) auprès d’un échantillon d’adolescentes. Nous visons également à examiner le rôle modérateur de l’anxiété dans ces associations. Notre échantillon est composé d’adolescentes (M = 15,55 ans; É-T = 1,64) issues de la communauté ou suivies dans le cadre de services sociojudiciaires (n = 200). Les résultats indiquent que les TIÉ sont associés à une empathie motrice plus faible, et que l’anxiété ne modère pas cette relation. Les TIÉ sont également associés à une empathie affective plus faible, mais pour cette forme d’empathie, l’anxiété jouerait un rôle modérateur. En effet, à mesure que les scores de TIÉ augmentent, les scores d’empathie affective diminuent, et ce, en particulier lorsque les scores d’anxiété sont faibles. Les analyses effectuées ne permettent pas de tirer de conclusions claires quant aux associations entre les TIÉ et l’empathie cognitive. Enfin, nous abordons le sujet des implications pratiques quant aux stratégies d’intervention découlant de nos travaux et quant aux travaux futurs. / Callous unemotional (CU) traits encompass a range of charact e ristics, such as superficial affects, a lack of remorse , guilt , and reduced empathic response to others' emotional states. Indeed, negative associations have been identified between CU traits and different forms of empathy, namely motor empathy, affective empathy, and cognitive empathy. Most of the research in this f ield has focused on samples of boys, limiting our understanding of the subject regarding girls. Moreover , the heterogeneity among ind ividuals with CU traits has not always been considered in previous studies. Anxiety is often considered as a distinguishing characteristic between two variants of CU traits, one characterized by high anxiety and the other by low anxiety. In this study, we aim to examine the associations between CU traits and various forms of empathy (motor, affective, and co gnitive) in a sample of adolescent girls. We also explore the moderating role of anxiety in these associations. Our sample comprises adolescent girls (M = 15.55 years; SD = 1.64) from the community or involved in socio legal services (n = 200). The results reveal an association between CU traits and a reduced motor empathy, with no moderation effect of anxiety. Additionally, CU traits are associated with a reduced affective empathy, and it appears that anxiety plays a moderating role in this association. As CU traits scores increase, affective empathy scores d ecrease, particularly when anxiety scores are low. The analyses did not lead to any clear conclusi ons regarding the associations between CU traits and cognitive empathy. Finally, we discuss the practical implications of our findings for intervention strategies and future research.

Master of Science / Department of Biology / Jesse B. Nippert / The Konza Prairie in northern Kansas, USA contains over 550 vascular plant species; of which, few have been closely studied. These species are adapted to environmental stress as imposed by variable temperature, precipitation, fire, and grazing. Understanding which plant traits relate to drought responses will allow us to both predict drought tolerance and potential future shifts in plant community composition from changes in local climate. Morphological and physiological measurements were taken on 121 species of herbaceous tallgrass prairie plants grown from seed in a growth chamber. Gas exchange measurements including maximum photosynthetic rate, stomatal conductance to water vapor, and intercellular CO[subscript]2 concentration were measured. All plants were exposed to a drought treatment and were monitored daily until stomatal conductance was zero. At this point, critical leaf water potential (Ψ[subscript]crit), an indicator of physiological drought tolerance was assessed. Other measurements include root length, diameter, volume, and mass, leaf area, leaf tissue density, root tissue density, and root to shoot ratio. Traits were compared using pair-wise bivariate analysis and principal component analysis (PCA). A dichotomy was found between dry-adapted plants with thin, dense leaves and roots, high leaf angle, and highly negative Ψ[subscript]crit and hydrophiles which have the opposite profile. A second axis offers more separation based on high photosynthetic rate, high conductance rate, and leaf angle, but fails to provide a distinction between C[subscript]3 and C[subscript]4 species. When tested independently, grasses and forbs both showed drought tolerance strategies similar to the primary analysis. Matching up these axes with long term abundance data suggests that species with drought tolerance traits have increased abundance on Konza, especially in upland habitats. However, traits that relate to drought tolerance mirror relationships with nutrient stress, confounding separation of low water versus low nutrient strategies. My results not only illustrate the utility of morphological and physiological plant traits in classifying drought responses across a range of species, but as functional traits in predicting both drought tolerance in individual species and relative abundance across environmental gradients of water availability.

The primary objective of this study was to investigate the entrepreneurial orientation of a vehicle management and sales company. This was done to help design recommendations to establish an entrepreneurial orientation in the company and enhance the personal traits of the company. A vast journey into the body of knowledge about entrepreneurship emerged when the literature review of Chapter 2 resulted in the leaders in the field, internationally and local, gave shape and depth to the study. The empirical study was conducted by distributing a questionnaire to a target population of 120 employees. A total of 41 questionnaires were received and was used to conduct a statistical analysis on. The reliability of the questionnaire was tested by calculating the Cronbach Alpha coefficients for all the variables of entrepreneurial orientation as well as the personal traits. The data was used to calculate the mean and standard deviations of the individual responses for all the variables. The analysis also included the relationship between different demographic information and the variables of the study to test for any significant differences in the means. Conclusions were drawn from the data extracted from the questionnaires and recommendations were made based on the conclusions and the data on the relevant topics identified in the study. An action plan that supports the data, conclusions and recommendations was designed to help the company enhance the entrepreneurial orientation as well as the companies’ entrepreneurial behaviour. The study concludes with measurements of the objectives as well as suggestions for further research on the topic. / MBA, North-West University, Potchefstroom Campus, 2015

The primary objective of this study was to investigate the entrepreneurial orientation of a vehicle management and sales company. This was done to help design recommendations to establish an entrepreneurial orientation in the company and enhance the personal traits of the company. A vast journey into the body of knowledge about entrepreneurship emerged when the literature review of Chapter 2 resulted in the leaders in the field, internationally and local, gave shape and depth to the study. The empirical study was conducted by distributing a questionnaire to a target population of 120 employees. A total of 41 questionnaires were received and was used to conduct a statistical analysis on. The reliability of the questionnaire was tested by calculating the Cronbach Alpha coefficients for all the variables of entrepreneurial orientation as well as the personal traits. The data was used to calculate the mean and standard deviations of the individual responses for all the variables. The analysis also included the relationship between different demographic information and the variables of the study to test for any significant differences in the means. Conclusions were drawn from the data extracted from the questionnaires and recommendations were made based on the conclusions and the data on the relevant topics identified in the study. An action plan that supports the data, conclusions and recommendations was designed to help the company enhance the entrepreneurial orientation as well as the companies’ entrepreneurial behaviour. The study concludes with measurements of the objectives as well as suggestions for further research on the topic. / MBA, North-West University, Potchefstroom Campus, 2015

Master of Science / Department of Agronomy / P. V. Vara Prasad / Grain sorghum (Sorghum bicolor L. Moench) is the fourth most important cereal crop grown throughout the semi-arid regions of the world. It is a staple food crop in Africa and Asia, while it is an important feed crop in the United States (US). More recently it is increasingly becoming important as a potential bioenergy feedstock crop around the world. The state of Kansas is the largest producer of grain sorghum in the US and contributes 40% of the total production. Drought is one of the major environmental factors limiting sorghum production in the semi-arid regions of the US, Asia and Africa. It is estimated that global crop losses due to drought stress exceed $10 billion annually. In crop production, drought stress can be classified into pre- or post-flowering. Even though the world collections of sorghum contain over 35,000 accessions, the genetic base currently used in breeding programs is very small (about 3%). Thus, it is important to identify diverse breeding lines for crop improvement. The diversity (association) panel consisting of 300 sorghum lines from all over the world was assembled for trait evaluation and association mapping. In this research these lines were grouped into the five major races (Figure 1) and 10 intermediate races of sorghum. The objectives of the research are to: (i) quantify the performance of the diversity panel under field conditions in Kansas, (ii) identify critical physiological traits affected by drought at both pre- and post-flowering stages of sorghum development, (iii) identify the most sensitive stage to drought stress during the reproductive phase of sorghum development and, (iv) test the feasibility of using a chlorophyll fluorescence assay (CVA) as a tool for identifying stay-green lines in grain sorghum during early stages of crop development. Field experiments were conducted in 2006 and 2007 in two locations in Kansas (Manhattan and Hays) under rain fed and irrigated conditions for the association panel. Objectives (iii) and (iv) were achieved with controlled environment experiments conducted in the greenhouse at the agronomy department, Kansas State University in 2006 and 2007. Results showed that there was large genetic variability among and within different races in the diversity panel for growth, physiological traits and yield components. Some genotypes showed yield stability across the different environments that were investigated. Drought significantly decreased seed number and harvest index across genotypes and races. In grain sorghum the period prior to flowering (panicle initiation) was the most sensitive stage to drought stress, in terms of its effect on seed-set, during reproductive development. A cell viability assay showed that there were significant differences in the loss of cell viability between leaf sample of stay green and non-stay green genotypes when leaf samples are collected in the morning and subjected to high respiratory demand. Therefore the chlorophyll fluorescence assay has potential as a tool for stay green trait screening at early stages of growth in grain sorghum.

Un des défis les plus pressants offerts aux écologistes des communautés actuellement consiste à prédire la réponse des assemblages d'espèces au changement environnemental global. Les études départageant la contribution de la variation observée à l'intérieur des espèces et entre les espèces à la variation fonctionnelle observée entre les communautés le long de gradients environnementaux spatiaux sont particulièrement utiles à cette fin. Elles permettent en effet d'évaluer la part que l'adaptation locale et la plasticité phénotypique (variation intraspécifique), en plus du renouvellement en espèces (variation interspécifique), pourraient jouer dans la médiation des changements environnementaux par les communautés végétales. Ce mémoire vise à évaluer la contribution de la variation intraspécifique au renouvellement en traits entre des communautés végétales le long d'un flanc de montagne, ainsi que les contextes environnementaux et écologiques dans lesquels une plus grande ou plus faible contribution de cette variation intraspécifique pourrait être attendue. Pour ce faire, j’ai quantifié la variation dans trois traits fonctionnels distincts (phénologie florale, surface foliaire spécifique et hauteur) entre, et à l'intérieur de 51 espèces végétales herbacées de sous-bois distribuées entre des communautés couvrant une transition de la forêt de feuillus à la forêt boréale (Parc national du Mont-Mégantic, Qc). Je présente également un nouveau cadre conceptuel établissant des hypothèses et prédictions sur les contextes environnementaux et écologiques pouvant déterminer la magnitude de la contribution de la variation intraspécifique à l'association trait-environnement entre les communautés végétales, que je teste à l'aide de ce jeu de données. Je rapporte que l'importance relative de la variation intraspécifique au renouvellement fonctionnel entre les communautés est dépendante de l'axe environnemental considéré, étant la plus forte le long d'axes non-climatiques, soit l'ouverture de la canopée et l'acidité du sol. Cette contribution est également déterminée de façon importante par la structure des réponses des espèces au gradient, en particulier par la direction et la magnitude de la variation intraspécifique dans l'espèce la plus abondante, la cohérence dans la direction de la réponse fonctionnelle des espèces à la variation environnementale et les patrons d'association trait-abondance à l'intérieur des espèces. Mon étude souligne l'importance de considérer les patrons sous-jacents à la contribution de la variation intraspécifique dans l'évaluation des sources de l'association trait-environnement entre les communautés végétales et propose des bases empiriques fortes pour améliorer les prédictions des réponses phénologique et végétative des communautés au changement environnemental global.

Sommaire : Comprendre le fonctionnement des écosystèmes est un enjeu crucial, en particulier dans un contexte de changements globaux. Afin de mieux prédire les processus écosystémiques, j’ai testé la précision et les limites des hypothèses du biomass-ratio de Grime (HBMR) et de l’annulation idiosyncratique (HAI), cette dernière étant une hypothèse originale de cette thèse. Pour cela, j’ai appliqué le principe du biomass-ratio aux traits fonctionnels, en employant la méthode des traits agrégés en communauté, pour estimer la réponse globale des espèces en mélange. La décomposition des litières plurispécifiques constitue un bon modèle biologique, pour lequel je me suis posé les questions suivantes : (1) est-ce que l’HBMR prédit bien les taux de décomposition en mélanges plurispécifiques ? ; (2) est-ce que le degré de variabilité de ces taux diminue pour des raisons biologiques avec l’augmentation de la richesse spécifique (RS) des mélanges (HAI) ? ; (3) est-ce que la variabilité des taux entre mélanges diminue quand les conditions abiotiques du site deviennent plus limitantes ? ; (4) considérant que les mélanges plus contrastés fonctionnellement sont susceptibles de développer plus d’interactions, est-ce que la déviation à la prédiction augmente avec la dispersion fonctionnelle des mélanges (« FDis », Laliberté & Legendre 2010) ? Cette thèse inclut deux expériences de décomposition en sachets à litières : (1) à Sherbrooke (QC, Canada) avec des microcosmes, impliquant des litières de six espèces d’arbres, décomposant seules et en mélanges et (2) sur trois sites au climat contrasté dans la région de Clermont-Ferrand (France) avec des litières de quatre espèces d’herbacées, décomposant seules et en mélanges. Les résultats montrent des déviations positives et négatives par rapport aux taux prédits, mais l’HBMR décrit bien la réponse moyenne des litières plurispécifiques. Bien que l’HAI ait été rejetée, les résultats montrent une convergence des taux observés vers les taux prédits quand (1) la RS des mélanges augmente, (2) l’échelle spatiale augmente et (3) le climat est plus limitant pour la décomposition. Enfin, malgré des corrélations entre FDis et interactions entre espèces dans les litières, cette relation n’est pas généralisable et l’hypothèse de corrélation positive entre FDis et déviation à l’HBMR a été rejetée. // Abstract : Understanding ecosystem functioning is a key goal in ecology, especially in the context of global changes. To better predict ecosystem processes, I tested the accuracy and the limits of Grime’s biomass-ratio (BMRH) hypothesis and a novel idiosyncratic annulment (IAH) hypothesis. I applied the biomass-ratio to functional traits, using the community-weighted means (CWM) to estimate the global response of species in mixtures. I studied the decomposition of litter species mixtures as a biological model and asked the following questions : (1) does the BMRH predict well the decomposition rates of mixed species litters? ; (2) does the degree of variability of these rates decrease with increasing species richness (SR) beyond that expected from purely mathematical causes (IAH)? ; (3) does the variability of rates between mixtures decrease with less favourable abiotic conditions for decomposition? ; (4) as more functionally contrasted mixtures are expected to develop more interactions, does the deviation from prediction increase with increasing functional dispersion in mixtures (« FDis », Laliberté & Legendre 2010)? This study involves two decomposition experiments using litterbags: (1) at Sherbrooke (QC, Canada), in microcosms, involving litters from six tree species, decomposed alone and in mixtures and (2) in three climatically contrasted sites in the region of Clermont-Ferrand (France) with litters from four herbaceous species, decomposed alone and in mixtures. Despite both positive and negative deviations from expectation occurring at all levels of SR, the BMRH well described the average response of mixed species litters. Although I rejected the IAH, the results showed a convergence to the predicted values based on CWM with (1) increasing the SR in mixtures, (2) increasing the spatial scale of the study and (3) a less favourable climate to decomposition. Finally, although there was a correlation between litter interactions and functional divergence, this relationship was not generalizable and I rejected the hypothesis of a positive correlation between FDis and the deviations from BMRH.