Analyse de la plasticité du puits reproducteur du colza suite à une suppression de boutons floraux : conséquences sur le rapport source:puits et le rendement

Diplôme : Dr. d'UniversitéWinter oilseed rape (WOSR) is a high value-added crop that needs high chemical inputs, including the insecticides. The most damaging pests are pollen beetles (Meligethes aeneus) that perforate buds to feed pollen in their stamina. Following these damages buds abort that causes yield losses for farmer. Currently, for both economic and environmental reasons, it is urgent to reduce use of insecticide on WOSR crops. Besides the genetic pathway, one solution is to promote integrated pest management and to enhance the capacity of WOSR to compensate bud losses. This strategy requires the identification of mechanisms involved in the compensatory process. To do this, we used a conceptual scheme which postulates that yield and architecture of plant are the results of the dynamic regulation between morphogenesis (producing organs) and sink:source relationships (which control the growth produced organs). The losses of flower buds, which correspond to the removals of sink organs (biomass consumer) modify this whole scheme. This work adress three main questions : (1). How are modified the dynamics of reproductive and vegetative morphogenesis after bud clippings ? (2). How are impacted sink:source relationships ? (3). What are the consequences of changes in morphogenesis and its regulation on both the plant yield and architecture ? Experiments were conducted to answer theses questions : they aimed to vary both (i) capacity of morphogenesis and (ii) the characteristics of the bud clippings. Thus, we chose to use (i) 3 varieties with contrasting architectures under 2 levels of nitrogen fertilization and to apply (ii) bud clippings with increasing intensities just before flowering. The main results of this work are: (1). After bud losses, there is an over-production of buds that is regulated by an increased in the number of aborted buds, which leads finally to a full compensation in the number of pods per plant. Our data failed to properly conclude on the effect of bud clippings on the date of leaf falling off ; however we observed a significant increase in the number of leaves per plant. (2). The loss of sinks increases the source:sink ratio, i.e the availability of assimilates, which allows the growth of organs involved in the compensation. These growths of new sinks induces a rapid return to initial value of source:sink ratio. (3). The release of assimilates allows the growth of organs involved in compensation, i.e the growth of new (i) primary basal fertile axes to compensate the loss of apical fertile axes affected by the clippings, (ii) secondary fertile axes. The growths of these compensatory organs does not alter the rules of biomass allocation between the different plant compartments. Finally, 93% of the tested combinations of Variety * Nitrogen fully compensate the applied clippings.Le colza est une culture à forte valeur ajoutée et aux débouchés florissants ; mais elle souffre d’un handicap majeur : sa forte consommation en intrants, parmi lesquels, les insecticides. Parmi les ravageurs de printemps du colza, le plus nuisible est le méligèthe (Meligethes aeneus). Ces insectes endommagent les boutons floraux lorsqu’ils se nourrissent du pollen contenu dans leurs étamines ce qui entraine une perte de rendement pour l’agriculteur. Actuellement, pour des raisons à la fois économiques et environnementales, il est urgent de réduire l’utilisation des insecticides sur les champs de colza. Outre la voie génétique, une des solutions est de favoriser la protection intégrée de la culture, et notamment de valoriser les capacités du colza à compenser une perte de boutons floraux. Cette stratégie nécessite l’identification des mécanismes impliqués dans le processus de compensation. Pour ce faire, nous avons utilisé un schéma conceptuel qui postule que le rendement et l’architecture d’une plante sont les résultantes de l’interaction dynamique entre la morphogenèse (production des organes) et les relations source:puits (qui pilotent la croissance des organes produits). La perte de boutons floraux, qui correspond à la suppression d’organes puits (consommateurs de biomasse) modifiant l’ensemble de ce schéma, la problématique de ce travail de thèse se décline en trois questions : (1). Comment sont modifiées les dynamiques de morphogenèse reproductrice et végétative ? (2). Comment sont impactées les relations source:puits ? (3). Quelles sont les conséquences de la modification de la morphogenèse et de sa régulation sur le rendement et l’architecture de la plante ? Les expérimentations menées ont eu pour objectif de faire varier à la fois (i) les capacités de morphogenèse et (ii) les caractéristiques de la perte d’organes. Ainsi, nous avons choisi d’utiliser (i) 3 variétés aux architectures contrastées sous 2 niveaux de fertilisation azotée et d’appliquer (ii) des ablations de boutons floraux d’intensités croissantes juste avant la floraison. Les principaux résultats de ce travail sont : (1). Suite à une perte de boutons floraux, il y a une sur-production de boutons floraux qui est régulée par l’augmentation du nombre de boutons floraux avortés ; ce qui mène au final à une pleine compensation en terme de nombre de siliques par plante. Nos données n’ont pas permis de conclure proprement sur la modification de la date de chute des feuilles suite aux ablations ; en revanche, nous avons observé une augmentation significative du nombre de feuilles par plante. (2). La perte d’organe puits entraîne une augmentation du rapport source:puits, i.e de la disponibilité en assimilats ; ce qui permet la croissance des organes impliqués dans la compensation. La mise en place des puits de compensation induit un retour rapide à l’équilibre initial des valeurs source:puits normales. (3). La libération des assimilats permet la croissance des organes impliqués dans la compensation ; à savoir, la mise en place de nouveaux (i) axes primaires basaux fertiles qui compensent la perte des axes fertiles apicaux touchés par les ablations ; (ii) axes secondaires fertiles. La mise en place de ces organes ne modifie pas les règles d’allocation de la biomasse entre les différents compartiments de la plante. Au final, 93% des combinaisons Variété*Fertilisation azotée testées compensent pleinement les dégâts infligés

Analyse comparative de la mise en place du rendement pour trois variétés de colza d'architectures contrastées : Capitol, Saturnin, et Pollen

spécialité Recherche AgronomiqueDiplôme : Masteril s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : DISSERTATIONabsen

Floral bud damage compensation by branching and biomass allocation in genotypes of Brassica napus with different architecture and branching potential

Plant branching is a key process in the yield elaboration of winter oilseed rape (WOSR). It is also involved in plant tolerance to flower damage because it allows the setting of new fertile inflorescences. Here we characterize the changes in the branching and distribution of the number of pods between primary and secondary inflorescences in response to floral bud clippings. Then we investigate the impacts of the modifications in branching on the biomass allocation and its consequence on the crop productivity (harvest index). These issues were addressed on plants with contrasted architecture and branching potential, using three genotypes (Exocet, Pollen, and Gamin) grown under two levels of nitrogen fertilization. Clipping treatments of increasing intensities were applied to either inflorescences or flower buds.We were able to show that restoration of the number of pods after clipping is the main lever for the compensation. Genotypes presented different behaviors in branching and biomass allocation as a function of clipping treatments. The number of fertile ramifications increased for the high intensities of clipping. In particular, the growth of secondary ramifications carried by branches developed before clipping has been observed. The proportions of yield and of number of pods carried by these secondary axes increased and became almost equivalent to the proportion carried by primary inflorescences. In terms of biomass allocation, variations have also been evidenced in the relationship between pod dry mass on a given axis and the number of pods set, while the shoot/root ratio was not modified. The harvest index presented different responses: it decreased after flower buds clipping, while it was maintained after the clipping of the whole inflorescences. The results are discussed relative to their implications regarding the identification of interesting traits to be target in breeding programs in order to improve WOSR tolerance

Are yield and biomass distribution affected by sink organ clipping during reproductive phase of winter oilseed rape (Brassica napus L.)?

As many crops, Winter Oilseed Rape plants are sensitive to biotic or abiotic stresses, but, due to its plasticity reproductive organ losses can be compensated. In this case, biomass is allocated to remaining organs changing yield distribution within the plant. However, compensation remains variable and causes of this variability are still not completely understood. Due to sequential development, pod yield is distributed among axes unevenly. Indeed biomass of axis and biomass allocation to pods varies according to axis position. We suppose that efficiency of compensation at plant scale would depend on the position of axis implied. In the following study axes were clipped. Yield and biomass distribution within plant as well as efficiency of biomass allocation to reproductive organs were characterized. Our data assume that basal axe were mainly involved in compensation and that increase in pod yield on these axes was related to increase in dry mass with no modification of the efficiency allocation of biomass

Identification of plant traits related to the tolerance of WOSR to pollen beetle

International audienc

Model calibration on two oilseed rape varieties (Brassica Napus L.), comparison and perspectives

Actes sur CDROMabsen

Levers of tolerance to floral bud damage in Brassica napus

poster, + poster abstractInternational audienc

Modelling of branch and flower expansion in GreenLab model to account for the whole crop cycle of Winter Oilseed Rape (Brassica Napus L.)

interesting tools to study interactions between architecture and environmental conditions. In the case of Winter Oilseed Rape (WOSR), we need a plant model that accounts for the role of source:sink relationships in the architectural development. GreenLab model is a good candidate because it was already used to evidence interactions between source:sink relationships and architecture for other species. However, its adaptation to WOSR is a challenge because of the complexity of its developmental scheme especially during reproductive phase. Indeed, we need to take into account the different timings of branch expansion and pod setting. Therefore two equations were added in GreenLab model to compute expansion delays for respectively branching and flowering of each axis.Experimental field data were used to estimate morphological parameters such as phyllochron, podochron,(equivalent to phyllochron but for pods), leaf expansion duration, and leaf life span. These data were also used to calibrate the source:sink module of the model. First results indicated that the model simulates properly the dynamics of plant growth and development during both vegetative and reproductive phases

Modelling of branch and flower expansion in GreenLab model to account for the whole crop cycle of Winter Oilseed Rape (Brassica Napus L.)

interesting tools to study interactions between architecture and environmental conditions. In the case of Winter Oilseed Rape (WOSR), we need a plant model that accounts for the role of source:sink relationships in the architectural development. GreenLab model is a good candidate because it was already used to evidence interactions between source:sink relationships and architecture for other species. However, its adaptation to WOSR is a challenge because of the complexity of its developmental scheme especially during reproductive phase. Indeed, we need to take into account the different timings of branch expansion and pod setting. Therefore two equations were added in GreenLab model to compute expansion delays for respectively branching and flowering of each axis.Experimental field data were used to estimate morphological parameters such as phyllochron, podochron,(equivalent to phyllochron but for pods), leaf expansion duration, and leaf life span. These data were also used to calibrate the source:sink module of the model. First results indicated that the model simulates properly the dynamics of plant growth and development during both vegetative and reproductive phases