Les risques de sécheresse sévère augmentent sous l’effet du changement climatique. Mieux comprendre les stratégies adaptatives des plantes au stress hydrique est ainsi l’un des défis majeurs de la recherche écologique et agronomique. Cette thèse explore la survie à la sécheresse d’une graminée herbacée pérenne (Dactylis glomerata L.) en étudiant la variabilité intraspécifique des traits aériens et souterrains d’une quinzaine de populations natives et cultivées issues d’un gradient latitudinal allant de la Scandinavie au Maroc. Une caractérisation des populations en conditions optimales sur une année a montré une coordination phénologique des traits aériens en relation avec les limitations saisonnières de croissances liées à l’origine des populations. Le rythme de croissance au printemps et à l’automne ne discrimine pas les origines, alors que la dormance estivale des populations méditerranéennes s’oppose à la dormance hivernale des populations scandinaves. Ces résultats suggéraient l’existence d’un compromis entre survie à une déshydratation sévère (sécheresse, gel) et potentiel de croissance. Alors que ce compromis a été vérifié en été (sècheresse sévère à Montpellier) et en hiver (gel en Norvège), la survie à une déshydratation de contre-saison au printemps n’est pas corrélée au potentiel de croissance des populations. Les résultats invalident donc l’existence d’un compromis constant entre survie au stress et potentiel de croissance aérienne. Ce découplage chez le dactyle permet d’envisager la sélection artificielle, à partir de la variabilité intraspécifique existante, de variétés à la fois productives et tolérantes au stress hydrique. L’imposition d’une déshydratation édaphique sévère en pots limitant l’expansion du système racinaire a montré que les populations méditerranéennes survivent mieux que les populations tempérées ou nordiques. L’association de ces résultats avec ceux issus d’une expérimentation en longs tubes favorisant le développement potentiel des racines révèle un compromis entre les stratégies d’évitement de la déshydratation (acquisition de l’eau et maintien de la croissance) et de tolérance à la déshydratation (faible croissance et forte survie à la sécheresse) qui pourrait limiter la combinaison de stratégies adaptatives au sein d’un même phénotype. Cette thèse contribue à améliorer notre compréhension des compromis fonctionnels, peu étudiés à l’échelle intraspécifique, mais qui sous-tendent la réponse des plantes à la sécheresse. / Drought risk increases with climate change. Improving our understanding of the adaptive mechanisms of plants response to drought has thus become one of the major challenges of ecological and agronomical research. This work investigates the drought survival of a perennial herbaceous species (Dactylis glomerata L.) through the intraspecific variability of above and below ground traits expressed by fifteen native and cultivated populations originating from a large latitudinal gradient, from Scandinavia to Morocco. Population traits characterization across one year under optimal growth conditions showed phenological coordination of above ground traits associated with seasonal growth limitations according to the origins of the populations. The spring growth rhythm does not discriminate origins while the summer dormancy of Mediterranean population contrasts with the winter dormancy of Scandinavian populations. These results suggested a growth-dehydration stress survival trade-off. Although this trade-off was confirmed in summer (severe drought in Montpellier) and winter (severe frost in Norway), no correlation was found between an off-season (spring) drought stress survival and populations’ growth potential. The result invalidates the existence of a constant trade-off between stress survival and aerial growth potential. This apparent decoupling in cocksfoot could be considered to produce new cultivars with both high productivity and high drought tolerance, from existent intraspecific variability. A severe dehydration stress imposed on plants grown in short pots, limiting roots expansion, showed that Mediterranean populations survived better than temperate or Nordic populations. In association with a long tube experiment allowing full expression of roots development, this result revealed a functional trade-off between dehydration avoidance (water acquisition and growth maintenance) and dehydration tolerance (low growth and high drought survival) which could limit the combination of adaptive strategies in a single phenotype. This work contribute to improve our knowledge about functional trade-offs, few studied within species, that underpin plant response to drought stress.

Agronomic and physiological traits associated with drought adaptation were assessed within the Seri/Babax recombinant inbred line population, derived from parents similar in height and maturity but divergent in their sensitivity to drought. Field trials under different water regimes were conducted over three years in Mexico and under rainfed conditions in Australia. Under drought, canopy temperature (CT) was the single-most drought-adaptive trait contributing to a higher performance (R2= 0.71, p<0.0001), highly heritable (h2= 0.65, p<0.0001) and consistently associated with yield phenotypically (r= -0.75, p<0.0001) and genetically [R(g)= -0.95, p<0.0001]. CT epitomises a mechanism of dehydration avoidance expressed throughout the growing season and across latitudes, which can be utilised as a selection criteria to identify high-yielding wheat genotypes or as an important predictor of yield performance under drought. Early response under drought, suggested by a high association of CT with estimates of biomass at booting (r= -0.44, p<0.0001), leaf chlorophyll (r= -0.22,p<0.0001) and plant height (r= -0.64, p<0.0001), contrast with the small relationships with anthesis and maturity (averaged, r= -0.10, p<0.0001), and with osmotic potential (r= -0.20, p<0.0001). Results suggest that the ability to extract water from the soil under increasing soil water deficit is a major attribute of drought adaptation. Ample genetic variation and significant transgressive segregation under drought suggested a polygenic governance feasible of dissection via molecular markers of CT and associated physiological and agronomic traits. Bulked segregant analysis of selected secondary traits was utilised as an alternative to complete genome mapping, due to a low polymorphism (27%) within the cross and limited chromosomic linkage of loci. The assessment of the extremes of expression in a genotypic subset with a composite molecular database of 127 markers (PCR-based and AFLPs) allowed evaluation of the three hexaploid wheat genomes and coverage of all chromosomic groups, except 3D. One-way analysis of variance indicated significant associations of loci explaining phenotypic variance under drought and rainfed conditions, of 20-70% in Mexico and 20-45% in Australia (F>5.00, p<0.05). Significant loci were established in both latitudes for all physiological and agronomic traits assessed via BSA, with CT being the trait with the most numerous associations (in Mexico, 34 loci; in Australia, 24). Results demonstrate an efficient development of molecular markers associated to physiological traits under specific soil water conditions in Mexico and Australia, and suggest further genomic and transcriptomic studies be conducted for unravelling the complex relationship between drought adaptation and performance under drought. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1284279 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2007

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Agronomic and physiological traits associated with drought adaptation were assessed within the Seri/Babax recombinant inbred line population, derived from parents similar in height and maturity but divergent in their sensitivity to drought. Field trials under different water regimes were conducted over three years in Mexico and under rainfed conditions in Australia. Under drought, canopy temperature (CT) was the single-most drought-adaptive trait contributing to a higher performance (R2= 0.71, p<0.0001), highly heritable (h2= 0.65, p<0.0001) and consistently associated with yield phenotypically (r= -0.75, p<0.0001) and genetically [R(g)= -0.95, p<0.0001]. CT epitomises a mechanism of dehydration avoidance expressed throughout the growing season and across latitudes, which can be utilised as a selection criteria to identify high-yielding wheat genotypes or as an important predictor of yield performance under drought. Early response under drought, suggested by a high association of CT with estimates of biomass at booting (r= -0.44, p<0.0001), leaf chlorophyll (r= -0.22,p<0.0001) and plant height (r= -0.64, p<0.0001), contrast with the small relationships with anthesis and maturity (averaged, r= -0.10, p<0.0001), and with osmotic potential (r= -0.20, p<0.0001). Results suggest that the ability to extract water from the soil under increasing soil water deficit is a major attribute of drought adaptation. Ample genetic variation and significant transgressive segregation under drought suggested a polygenic governance feasible of dissection via molecular markers of CT and associated physiological and agronomic traits. Bulked segregant analysis of selected secondary traits was utilised as an alternative to complete genome mapping, due to a low polymorphism (27%) within the cross and limited chromosomic linkage of loci. The assessment of the extremes of expression in a genotypic subset with a composite molecular database of 127 markers (PCR-based and AFLPs) allowed evaluation of the three hexaploid wheat genomes and coverage of all chromosomic groups, except 3D. One-way analysis of variance indicated significant associations of loci explaining phenotypic variance under drought and rainfed conditions, of 20-70% in Mexico and 20-45% in Australia (F>5.00, p<0.05). Significant loci were established in both latitudes for all physiological and agronomic traits assessed via BSA, with CT being the trait with the most numerous associations (in Mexico, 34 loci; in Australia, 24). Results demonstrate an efficient development of molecular markers associated to physiological traits under specific soil water conditions in Mexico and Australia, and suggest further genomic and transcriptomic studies be conducted for unravelling the complex relationship between drought adaptation and performance under drought. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1284279 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2007

Covering various aspects of the environmental approach, this diploma thesis mostly deals with the anthropological context of drought in the selected vineyards in Prague, the Czech Republic. This research embodies an ethnographic probe into the specific part of Czech viticulture. Based on the participatory observation methods and semi-structured interviews, the author describes the daily routine of winemaking on the Grébovka vineyard and the wider context of drought in several Prague vineyards. Research shows that winemakers who manage these vineyards experience different levels of drought and their responses to this phenomenon in the form of common agricultural adaptation mechanisms are influenced by factors arising mainly from the very nature of viticulture, the local conditions and specifics of these city vineyards and the involvement of all actors in the vineyard, that form a network in which they are interconnected and interact in a particular way. In this thesis the author also reflects these local dimensions and contexts of drought as one of the consequences of climate change in the broader context of (anthropology) of climate change. Based on her research, the author mainly discusses the issue of scientific forecasting, because this scientific vision of the future can differ significantly...