Assessment of the water stress effects on peach fruit quality and size using a fruit tree model, QualiTree
Introduction
Regulated deficit irrigation (RDI) practices are common for peach-tree cultivation in order to save water. This may impose serious water restrictions to the trees. For instance, in Spain, where peach (Prunus persica L. Batsch) culture is highly important, restrictions in irrigation water are usually imposed in midsummer, before the harvest of many mid-late maturing cultivars (Lopez et al., 2010); this coincides with the final stage of fruit development (stage III), which is characterised by a high accumulation of fresh and dry weight by the fruit.
Those water restrictions not only may have an effect on fruit size, but also on fruit quality, which is an important issue for fruit production and retailing (Codron et al., 2005). For instance, Berman and DeJong (1996) reported that water stress at stage III limits fruit growth. Hence, marketable fruit size may not be attained. However, other fruit quality criteria could be positively affected, such as soluble solid content in fruit flesh (Crisosto et al., 1994). In this sense, Lopez et al. (2010), studying deficit-irrigated mid-late maturing ‘O’Henry’ peach, found that RDI significantly increased soluble solid contents. On other species from the Prunus genre, such as plum, deficit irrigation has also been reported to increase total soluble solids content in fruits (Intrigliolo and Castel, 2010).
Fruit quality involves a set of traits such as fruit size, overall composition and taste, and proportion of edible tissue (Génard et al., 2009). These traits result from many processes at both the plant and organ levels that show large genotype × environment (management) interactions (Aguirrezábal et al., 2009). Understanding all the interactions between factors affecting fruit quality and the inherent complexity of its build-up is a challenging subject. In this sense, process-based simulation models may be useful tools to discern the complex linked processes controlling fruit size and composition at different levels of organisation (Martre et al., 2011). Although several models for simulating fruit-tree functioning have been developed for apple (Costes et al., 2008) and peach (L-PEACH: Allen et al., 2005), accounting for the effect of water stress on carbon partitioning in the latter case (Da Silva et al., 2011), they are not focused on fruit quality. Recently, Lescourret et al. (2011) presented QualiTree, a model that combines physiological and agronomic viewpoints for describing carbon allocation within the tree, vegetative and fruit growth distribution and the development of fruit quality. Because of its parsimony, QualiTree is more convenient than the previous models for quantitative comparison of data for parameterisation and evaluation.
In its present state, QualiTree has not been validated with experimental data on sugar concentrations in fruit flesh. Furthermore, the results reported by Mirás-Avalos et al. (2011) suggest that some parameters within QualiTree are cultivar-dependent. Therefore, the aim of the present work was to validate QualiTree sugar sub-model for a mid-maturing peach tree cultivar (the previous studies were done on early and late maturing cultivars, Mirás-Avalos et al., 2011, Mirás-Avalos et al., 2012) and to use the predictive capabilities of the model for evaluating the effects of water restrictions on fruit and vegetative growth, and also on sugar concentrations in the fruit flesh.
First, QualiTree was parameterised for a mid-maturing peach cultivar (cv. ‘Catherine’) and validated with observed data from different situations concerning irrigation conditions. The variables considered were the fruit and the leafy shoot dry masses, and the concentrations of four sugars (sucrose, glucose, fructose, and sorbitol) in the fruit. Then, we designed several simulation scenarios to observe the response of the model. Some of these scenarios were theoretical for testing the behaviour of the model and some others were constructed using field observations involving deficit irrigation practices as a basis.
Section snippets
QualiTree, model overview
QualiTree (Lescourret et al., 2011) is a generic fruit tree model that describes the tree as a set of objects: fruiting units (FU) composed of fruits, leafy shoots and stem wood in a tree architecture, and other compartments viewed globally: old wood (trunk and branches), coarse roots, and fine roots. QualiTree runs, on a daily timestep, from bloom or after bloom until the end of the fruit growing season, starting from an initial state of the tree.
In order to represent the growth in dry mass of
Parameterisation and test of the model
Parameter values are indicated in Table 1. Interestingly, a very low value of the parameter expressing the effect of distance between tree objects on carbon exchange within the tree (k) was observed (Table 1). This indicates within-tree distances are not a limitation. It is also worth noting that the rate of sorbitol transformation to fructose (k3) was greater than that to glucose (k2) (Table 1).
Simulated leafy shoot dry masses fitted correctly those observed. The variability of the simulated
Discussion
A middle-late maturing peach cultivar (‘Catherine’) was successfully implemented and parameterised into QualiTree, a virtual tree model (Lescourret et al., 2011) that simulates the within-tree variations in fruit and leafy-shoot dry masses. The parameterisation of this middle-late maturing peach cultivar broadened the predictive capacities of the model, since certain parameters within QualiTree are cultivar dependent (Mirás-Avalos et al., 2011, Mirás-Avalos et al., 2012). Several parameters
Acknowledgements
We are grateful to the IRRIQUAL (EU-FP6-FOOD-CT-2006-023120) and SIRRIMED (KBBE-2009-1-2-03, PROPOSAL No. 245159) projects for financial support. We also acknowledge two SENECA projects (05665/PI/07 and 11872/PI/09) and CONSOLIDER INGENIO 2010 (MEC CSD2006-0067) and CICYT (AGL2010-17553) projects for funding this research. J.M. Mirás-Avalos thanks Xunta de Galicia for funding his contract within the framework of the program “Isidro Parga Pondal”.
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