Croissance et qualité organoleptique de la mangue (Mangifera indica) : analyse expérimentale et modélisation de l'effet de la disponibilité hydrique et carbonée

In this work, the effects of water and assimilate supplies on processes involved in mango fruit quality were investigated, in order to contribute to understand the intra-crown heterogeneity of mango fruit quality. By an experimental approach, a strong link was found between water and carbon accumulation in each fruit component (peel, pulp and stone) regardless of treatments. The pulp is the component for which the size increased the most with the leaf-to-fruit ratio. Fresh mass and dry matter content are the main quality traits affected by assimilate supply in mango. Calcium, malic and citric acids, and fructose concentrations were higher, and those of sucrose were lower in fruits from treatment with the lowest assimilate supply. In our conditions, water supply affected weakly mango fruit quality. The effects of assimilate supply on source/sink balance at the shoot bearing fruit level was analysed by experiments and models. The model computed processes as leaf photosynthesis, maintenance and growth respiration, reserves storage and mobilisation in leaves and stem, and fruit growth. Simulations using various climatic conditions were used to assess the respective contribution of climate changes, initial fruit dry mass and leaf-to-fruit ratio on processes involved in fruit growth. Plant and fruit relations (water potential, turgor and osmotic pressures) and diurnal fruit growth were determined for studying and modelling reversible and irreversible enlargement processes in mango. The model simulates changes in elastic and plastic fruit growth under various assimilate supplies, with a set of parameters, as the elastic modulus, the cell wall extensibility and the yield threshold pressure which may change during the growth in mango, as we proposed in the model. Simulations in shortage of water or assimilate supply were analysed to study how it affects fruit water relations and fruit composition and the consequences on fruit fresh mass. Those models were integrated in a global model which predicts at harvest fruit quality traits, like fruit fresh mass, dry matter content, and the main non structural compounds involved in sourness, sweetness, and shelf life. Simulations have shown that early fruit size affects positively fruit growth. Increased early fruit size improves eating quality at harvest (sweetness, sourness) but reduces quality aspects linked to shelf life. Further studies are suggested in order to generalize this ecophysiological approach at the tree level and to the application of our global model to genetic variability analysis of mango fruit quality or to propose practical consequences of this work. (Résumé d’auteur)