The model
- Simulating genotypic variation of fruit quality in an advanced peachxPrunus davidiana cross

The model integrates three sub-models developed independently, all concerning the stage of fruit enlargement at the end of cell division. The modelled system is the ‘shoot bearing fruit’ which is represented by three interconnected compartments: fruits including flesh and stone, 1-year-old stems, and leafy shoots. The focus here is on the processes that particularly relate to the fruit quality issue, giving emphasis to equations that were added or modified to describe the behaviour of wild genotypes. The main variables predicted by the integrated model are dry and fresh masses of fruit and stone, flesh dry matter content, and total sugar amount and concentration in the flesh. The parameters are presented in Table 1. (Details about the processes described by the sub-models and the equations are given as supplementary data in the Appendix which is available at JXB online.)

The carbon assimilation and allocation sub-model (Lescourret et al., 1998; Génard et al., 1998; Quilot et al., 2002) simulates carbon partitioning based on organ demand and priority rules. Flesh growth potential demand was described in terms of degree-days by a logistic equation (see Equation 9 of the Appendix in the supplementary data at JXB online) which enabled both logistic and exponential growth to be described by modifying the value of the parameter which contributes to the slowing down of growth with the maturation process. Since the population studied showed high variation in stone versus flesh partitioning, an equation relating stone growth to fruit growth (see Equation 10 of the Appendix in the supplementary data at JXB online) was added to describe the potential stone growth. Sugar accumulation is simulated by a simple sub-model that predicts the increase of total sugar concentration in the flesh during fruit growth (Quilot et al., 2004b). A function depending on the thermal time describes the partitioning of total sugar between sucrose and other sugars for each genotype (see Equation 17 of the Appendix in the supplementary data at JXB online). The sub-model of water flux simulates fruit growth in fresh mass (Fishman and Génard, 1998). The rate of change of the amount of water in the flesh is computed daily from the water flux through xylem and phloem and the water loss due to fruit transpiration.