Le fraisier diploïde (Fragaria vesca, 2x=14) comporte deux modes de reproduction : la reproduction sexuée via la floraison, et la multiplication végétative via la production de stolons. Cette espèce présente également deux types de floraison, non-remontants ou remontants, selon la période d’initiation florale du génotype. Chez le fraisier diploïde, le gène responsable de la remontée florale a été identifié comme étant l’homologue du répresseur floral TFL1 et celui du stolonnage reste inconnu. L’objectif de cette thèse est d’identifier le gène responsable du stolonnage et de mieux comprendre la balance entre les deux modes de reproduction, sexuée et asexuée, chez le fraisier diploïde. Une approche de cartographie fine associée à du NGS a permis d’identifier le gène responsable du stolonnage, FvGA20ox4. Ce gène intervient dans la voie de biosynthèse des gibbérellines. Les génotypes non-stolonnants présentent une délétion de neuf bases qui ne modifie pas le cadre de lecture du gène. L’observation cytologique des méristèmes axillaires montre que les génotypes mutés présentent un allongement des axillaires comme les génotypes sauvages mais que ces bourgeons nécrosent par la suite. Une étude de l’activité enzymatique de la protéine délétée de trois acides aminés a montré qu’elle était inactive et ne permettrait pas de transformer les précurseurs de GA (GA12) en GA intermédiaires, qui seront convertis en GA actives via d’autres enzymes. Chez les génotypes mutés, un apport de GA3 permet de restaurer l’émergence de stolons. L’étude de la balance entre les deux modes de reproduction a été étudiée au sein d’une population en ségrégation pour le stolonnage et la remontée florale. Une approche QTL a permis de confirmer le rôle des gènes TFL1 et GA20ox4 dans le devenir des méristèmes en floral ou stolon respectivement et d’identifier deux loci présents sur le LG3 et LG4 impliqués dans la variation quantitative de la floraison ou du stolonnage respectivement. Pour le stolonnage, une interaction forte entre TFL1 et GA20ox4 a été mise en évidence par ANOVA. De plus, le suivi hebdomadaire de cette population pendant deux ans a montré que le processus de remontée florale prédominait celui de stolonnage. En conclusion, les données obtenues permettent une meilleure compréhension du stolonnage et de la balance entre les deux modes de reproduction chez le fraisier diploïde. / The diploid woodland strawberry (2n=2x=14) is a good model for genetic and genomic studies since it presents a small genome completely sequenced and its generation period is short. This species displays two modes of reproduction, sexual with flowering and vegetative through runnering, which is the capacity to form stolon. In addition, this species displays contrasted genotypes for their variation of flowering length because of difference in the period of floral initiation. This trait is under the control of TFL1. However, the genetic and molecular control of vegetative reproduction is poorly understood as the one of the balance between the two modes of reproduction. The objective of this work was to characterize the gene responsible of runnering and to decipher genetically and physiologically the balance between the two modes of reproduction. By developing a strategy combining linkage map, bulks and NGS, we found that runnering is controlled by the gibberellin (GA) oxidase, FvGA20ox4. The loss of runnering function is caused by a deletion of nine nucleotides, which does not change the open reading frame of the RNA and leads to a protein shortened by three amino acids. The GA oxidase activity was confirmed in enzymatic activity assays with recombinant protein. In addition, the loss-of-function can be restored by exogenous GA3 application. The genetic architecture of the balance between two reproductive modes, sexual and vegetative, was deciphered based on QTL approach. Results showed that, beside the known roles of TFL1 and GA20ox4 genes in promoting perpetual flowering and runnering processes respectively, two loci localized on LG4 and LG3 were linked to the quantitative responses of these processes. In addition, TFL1 and GA20ox4 genes showed epistatic interaction, and the process of flowering was maintained as priority over runnering, which decreased. These results provided new insight in the genetic control of the relationship between sexual and vegetative reproduction.

Abstract Peppermint (Mentha x piperita L.) oil is one of the most popular and widely used essential oils, mostly because of its main components menthol and menthone. Peppermint oil is used for flavouring pharmaceuticals and oral preparations. Corn mint is the richest source of natural menthol. Carvone-scented mint plants, such as spearmint (M. spicata), are rich in carvone and are widely used as spices, and they are cultivated in several countries. Studies were made into the yield and essential oil content of several mint species and the original. The general aim of the work was to examine the optimal conditions for cultivating mint in Northern Finland. The specific aims of the study were (first) to investigate the differences in the oil content for several mint species and (secondly) to compare the effect of various factors such as plant spacing (10, 20 and 30 × 50 cm), liming (0, 4, 8, 12 and 16 tons ha-1), propagation methods (micropropagated and conventionally propagated plants) and harvest date (once at the end of August in comparison with first cut at the beginning of August and second cut in mid September) on the cultivation success, quality and quantity of the plants. The constituents of the essential oil were analysed from leaf samples using GC-MS. Among the peppermints of different origins studied, peppermint of USA and Egypt origin ('Black Mitcham') contain the highest menthol and optimum oil yield. Corn mint and Sachalin mints both had high menthol content. Due to several reasons, such as no significant differences between the different densities and oil composition, markedly higher amount of weeds at 30 × 50 cm than at 10 × 50 and 20 × 50 cm spacing and the high seedling costs and the danger of fungi and disease at a 10 × 50 cm spacing, a plant optimum of 20 × 50 cm spacing is recommended for Northern Ostrobothnia. If the pH value is lower than 6, or levels of Mg and Ca are low, liming at a rate of 4–8 t ha-1 for sandy soils in Finland is recommended in order to achieve higher fresh and oil yields. In the first year, there were no differences in the dry leaf yield of micropropagated and conventionally propagated plants, but the menthol content was significantly higher in conventionally than in micropropagated plants. In the second year, only the dry leaf yield of micropropagated plants was higher than that of their conventionally propagated counterparts. Cutting peppermint only once during full bloom (the end of August) gives the maximum oil yield of good quality. In conclusion, it is possible to achieve as high as or even higher oil quality and dry yield in North Ostrobothnia than it is in central Europe or south Asia. However, this requires observing certain cultivation factors such as having the right type of mint, soil pH, planting density, harvesting time and propagation method In addition, mints must be cultivated in the same place for only two and a maximum for three years.