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Analyzing and modelling the genetic variablility of aerial architecture and light interception of the oil palm (Elaeis guineenis Jacq)

Perez R.. 2017. Montpellier : Montpellier SupAgro. Thèse de doctorat -- Biologie, interactions, diversité adaptative des plantes.

The development of new breeding strategies to find more sustainable and productive systems is a major challenge to cope with ceaseless increasing demands for vegetable oils, notably palm oil. Optimizing plant architecture to increase radiation interception efficiency could be an option for enhancing potential oil palm production. Indeed, studies in cereals showed great improvement of yields by altering plant architecture, in combination with agronomic practices. By analogy, we proposed to investigate the influence of oil palm architecture on the capacity of the plant to intercept light, by using 3D reconstructions and model-assisted evaluation of radiation-use efficiency. The first objective of this study was to analyse and model oil palm architecture and light interception taking into account genetic variability. A second objective was to explore the potential improvement in light capture and carbon assimilation by manipulating oil palm leaf traits and propose architectural ideotypes. Data were collected in Sumatra, Indonesia, on five progenies (total of 60 palms), in order to describe the aerial architecture from leaflet to crown scales. Allometric relationships were applied to model these traits according to ontogenetic gradients and leaf position within the crown. The methodology allowed reconstructing virtual oil palms at different stages over plant development. Additionally, the allometric-based approach was coupled to mixed-effect models in order to integrate inter and intra progeny variability through progeny-specific parameters. The model thus allowed simulating the specificity of plant architecture for a given progeny while including observed inter-individual variability. The architectural model, once parameterized for the different progenies, was then implemented in AMAPstudio to generate 3D mock-ups and estimate light interception efficiency, from individual to stand scales. Model validations were performed at different scales. Firstly at organ scale, the geometry of the stem, the leaves and the leaflets were compared between virtual mock-ups and actual plants measured in the field. Secondly, at plant scale with indicators derived from terrestrial laser scanning (TLS) to assess crown dimensions and porosity. These indicators integrated topological and geometrical information related to the amount of light intercepted by an individual. Finally, validations were performed at plot scale using hemispherical photographs (HP) to assess the variability of canopy openness for the five studied progenies. Significant differences in leaf geometry (petiole length, density of leaflets and rachis curvature) and leaflets morphology (gradients of leaflets length and width) were detected between and within progenies, and were accurately simulated by the modelling approach. The comparison of plant area obtained from TLS and virtual TLS highlighted the capacity of the model to generate realistic 3D mock-ups. The architectural variabilities observed at plot scale between and within progenies were also satisfactory simulated. Finally, light interception estimated from the validated 3D mock-ups showed significant variations among the five progenies. Sensitivity analyses (Morris method and metamodelling approach) were then performed on a subset of architectural parameters in order to identify the architectural traits impacting light interception efficiency and potential carbon assimilation over plant development. Daily carbon assimilation was estimated with a photosynthesis model coupled to the radiative balance model, which enabled to integrate the temporal and spatial variations of photosynthetic organ irradiances. The most sensitive parameters over plant development were those related to leaf area (rachis length, number of leaflets, leaflets morphology), although fine attribute related to leaf geometry showed increasing influence when canopy got closed. In adult stand, optimized carbon assimilation was estimated on plants presentin...

Mots-clés : elaeis guineensis; houppier; morphologie végétale; variation génétique; production forestière; lumière du jour; photosynthèse; architecture des arbres

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