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

60 M. Génard and F. Lescourret
allocation between sinks in the shoot bearing fruit. The model named ‘CaShoo’ is
described in details in Lescourret et al. (1998a). It was designed to especially analyse
the variation of mean peach fruit growth in terms of dry mass between shoots in
different conditions (leaf-to-fruit ratio resulting from thinning patterns, light environment;
Génard et al., 1998).
4.2.1. CaShoo: Carbon balance in the Shoot bearing fruit
The system is divided into three compartments: fruit, one-year-old stem, and leafy
shoots, and evolves on a daily basis. The pool of C assimilates available daily is
the assimilation of leaves and eventually that mobilized from reserves.
Several authors have reported a feedback inhibition of leaf photosynthesis through
the leaf storage carbohydrates (Guinn and Mauney, 1980; Foyer, 1988; Flore and
Lakso, 1989). A simple negative linear relationship between the light-saturated
max leaf photosynthesis Pl , and the level of reserves in the leaves is used in the
model. On this basis, the model uses the formulation of Higgins et al. (1992) to
calculate the photosynthesis (P)
max
P = {(Pl + p1) × ((1 – e
–p 2 × PPFD
P l max + p1 )} – p 1 (1)
where p 1 and p 2 are parameters, PPFD is the photosynthetically active photon flux
density (input data). Carbon assimilation by the fruit is considered on a similar basis.
The carbon is allocated according to organ requirements and priority rules.
Maintenance respiration costs are calculated on the basis of the Q10 concept and
are given first priority. Vegetative and fruit growth are given second and third
priority. The daily carbohydrate demand for growth by any organ is the daily
potential sink strength devoted to growth (Ho, 1988), as the potential net gain of
C plus the C loss due to growth respiration. A very general formulation of daily
carbon demand D i for the growth of a compartment composed of n individual organs
i (i.e. n fruits or n leafy shoots) can be written as
Di = n × ∆Wpot i
∆dd
∆dd
× × (CCi + GRC
∆t
i) (2)
pot where (∆Wi /∆dd) is the potential growth of the structural part of the organ in
terms of degree-days after full bloom dd, CCi the carbon concentration and GRCi the growth respiration coefficient of the organ i.
The following equation is proposed for potential fruit growth rate. It emphasizes
the role of fruit history by means of the accumulated growth Wf. It also
emphasizes the role of time by means of accumulated degree-days.
∆W f pot
∆dd
Wf max Wf ini = RGRf × Wf × ( 1 – ) × f(dd) (3)
with f(dd) = 1 if dd < dd min