According to climate change projections, increasing temperature and reduced water availability are expected in the near future. Therefore, growers must adapt their production systems, minimizing the negative effects of water scarcity, such as lower yields, and maximizing those positive, such as fruit-quality improvements. In this sense, process-based models could be useful tools for assessing fruit-tree responses to different irrigation strategies and support decision-making at the orchard level. In this study, an existing fruit-tree model (QualiTree) was adapted for describing the water stress effects on peach (Prunus persica L. Batsch) vegetative growth, fruit size and composition. New modules for calculating energy balance and water transfer at each fruit-bearing shoot, the growth of water sprouts and a vegetative growth reduction function dependent on tree water status, were implemented in QualiTree. Then, QualiTree was parameterized and calibrated for a late-maturing peach cultivar (‘Elberta’) using data collected under semi-arid conditions in Iran, under three different water irrigation treatments, corresponding to low, moderate and severe water stress. These different irrigation practices were simulated and outputs were compared with experimental data. Fruit and vegetative growth variability over time was consistent with observed data on trees submitted to different irrigation levels. Fruit size class distribution shifted toward smaller sizes as water deficit intensified. Sugar concentrations in fruit flesh were well simulated. In general, the relative mean square errors were low. According to simulations, severe water deficit decreased fruit, leafy shoot and water sprout dry masses by 31, 44 and 91%, respectively, but increased fruit sugar concentrations by 30%, when compared to the low stress treatment. The new implementations allowed QualiTree to represent the within-tree variability of water status and its effects on vegetative and fruit growth, as well as on fruit composition, demonstrating the usefulness of QualiTree for designing innovative horticultural practices under various climate change scenarios.

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