Production Practices and Quality Assessment of Food Crops. Vol. 1

f(dd) = dd max – dd
dd max – dd min
f(dd) = 0 if dd > dd max
Modelling Fruit Quality 61
if dd is between dd min and dd max
ini max where RGRf is the initial relative growth rate, Wf refers to the limiting final
mass and ddmin and ddmax are parameters.
A similar equation has been proposed for potential vegetative growth rate. Finally,
if the carbohydrate pool is not empty after allocation to the fruit, it is stored, first
in the leafy shoot and then in the one-year-old stem.
4.2.2. CaShoo, a tool to analyse the behaviour of shoots bearing fruits
The ability of the model to reproduce the effects of the shoot-to-fruit ratio was
studied, by comparing simulation outputs with experimental data. The model outputs
were consistent with the general pattern of vegetative growth (Figure 5) which shows
no clear differences between shoot-to-fruit ratio treatments.
Corresponding reproductive growth was quite well simulated, with smaller fruit
growth for lower shoot-to-fruit ratio (Figure 5). For the lowest shoot-to-fruit ratio,
the reserves decreased quickly to reach a nil value at 600 degree-days after bloom
and refilled itself after 1200 degree-days after bloom. This results in a high photosynthesis
activity during all the season. On the opposite, the reserves are never
nil and increase during the season with high shoot-to-fruit ratio which tends to inhibit
photosynthesis (Figure 6). This result is interesting for reasoning horticulture
practices. The presence of more assimilates than required during summer in case
of high shoot-to-fruit ratio, could improve bud initiation and development for the
next season.
The model was used to study the effect of source and sink factors on fruit mass
at harvest. The factors studied were selected by considering that the source (or
sink) strength is the product of a source (sink) size by a source (sink) activity.
The “initial” size of leafy shoots (i.e., that established at the beginning of active fruit
growth) was chosen as an indicator of source size because it was hypothesised to
determine the potential growth of leafy shoots (Lescourret et al., 1998a). The light
environment of the shoot bearing fruit was selected as it determines source activity.
Its heterogeneity throughout the tree canopy, which has been emphasised by Lakso
et al. (1989), Génard and Baret (1994) and Kikuchi et al. (1994), causes a large
variation in photosynthesis within the tree (Marini and Marini, 1983). Based on
the observations of Davis and Davis (1948) and Batjer and Westwood (1958), which
have indicated that the size of the fruit at the early stages of growth seemed to
influence fruit growth, the initial size of the fruit was hypothesised to contribute
to sink size. Finally, sink activity was considered by comparing early and late
maturing cultivars, which have different potential relative growth rates of fruit.
For each cultivar, the previous factors were considered at three levels (low,
intermediate and high). One run was performed per combination of factors. The
results of the simulations were analysed by analysis of variance (fixed effects).
The contribution of the different sources of variation, measured as the corresponding