Résumé
Tropical japonica rice is frequently exposed to drought in upland ecosystems. Its drought tolerance is poor compared to other crops but the group has great genetic, in part unexploited diversity in adaptations. Exploring the japonica's phenotypic and genetic diversity for drought tolerance is thus crucial to breed rice for drought prone environments. Under such conditions, yield depends on drought timing and intensity along plant phenology. During the vegetative phase, drought affects vigour (leaf number and area, tillering, roots) and therefore resource acquisition. Plant adaptation to drought is a complex mix of physiological tolerance, phenology and morphology, all of which interact with each other and with environment, resulting in phenotypic plasticity. This involves variable regulation of source-sink relationships during morphogenesis (phyllochron, organ expansion, tillering), leaf senescence and transpiration. Studying this system requires dissection into simpler traits involving a smaller number of genes/alleles. However, trait dissection must also account for Genotype*Environment (GxE) interactions and trait plasticity. This is particularly difficult for process based traits that cannot be measured directly. In this context, modelling is relevant if used to dissect a complex system into elemental processes. Each process can be formalized as a response function, with parameters seen as being analogous to genes. The objective of this work is to explore the added value of using dynamic whole plant modelling to assist phenotyping plant response to drought, as a basis for a genetic association study. This work focuses on rice plant transpiration and morphogenesis processes evaluated on seedlings of a diverse sample of tropical japonicas. A greenhouse pot experiment was conducted at Cirad, Montpellier, on 203 japonica accessions with three replications and two treatments (irrigated and drought). Drought was imposed by dry-down from leaf-6 appearance until a targeted stress level was reached, as indicated by Fraction of Transpirable Soil Water (FTSW). FTSW and plant transpiration rates were monitored gravimetrically. At the same time a minimum set of morphological plant descriptors and climate were collected, in order to calibrate, for each genotype and in both well watered and stressed conditions, the corresponding modules of EcoMeristem plant growth model . This paper presents first results and discusses the discriminative power and the added value of model assisted phenotyping for the case of rice drought responses. (Texte intégral)