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

48 M. Génard and F. Lescourret
the scientific knowledge issued from functional genomics or to properly consider
biotechnological advances.
Our objective is to present the conceptual basis needed to develop such models
in horticulture, focusing on fruit quality. Biological models useful to orchard
management need to integrate knowledge in several fields of research, mainly
ecophysiology which analyses the physiological process of fruit quality elaboration,
agronomy which considers cropping operations and their effect on quality,
and ecology which analyses the dynamics of pests and diseases. In the first parts
of this chapter, the complexity of fruit quality will be underlined and the current
knowledge in biological modelling of fruit quality will be presented across several
fields of science. Then, we will use the models developed in our team to show
how knowledge in these fields can be used at different scales of analysis, from
the fruit to the orchard.
2. FRUIT QUALITY: A MULTI-CRITERIA CONCEPT
AND A COMPLEX PROBLEM
According to Arthey (1975), ‘the quality of a horticultural product is assessed
from the relative values of several characteristics which considered together will
determine the acceptability of the product to the buyer and ultimately the consumer’.
Quality is a multi-criteria concept which is not so easy to consider in modelling.
For instance, the quality of fleshy fruits such as pears, cherries or peaches, depends
on their sugar content (Leonard et al., 1953; Robertson et al., 1992) and more
specifically on the distribution of this content between the different sugars that
directly influence fruit flavour components such as sweetness (Robertson et al., 1988;
Byrne et al., 1991). Sucrose, glucose and fructose which are the main sugars in
the fruits of most plants have different sweetness (Pangborn, 1963; Yamaguchi et
al., 1970; Doty, 1976). Moreover, each quality criterion is per se the result of a
complex chain of biological processes. Let us consider sweetness. It results from
hundreds of processes involved in sugar production in the leaves, loading and
translocation in the phloem, unloading in the fruit cells, metabolism in the fruit cells
and dilution by the water accumulated in the fruit. The technical operations applied
to the orchard influence these processes in a complex way. That is why current
agricultural practices result in a wide variability of the sugar contents in fruits
from different plots, from trees of the same plot or from one part of the plant to
another (Marini and Trout, 1984; Dann and Jerie, 1988). This variability is caused
by various factors such as water availability (Besset et al., 2001), microclimatic
gradients (Corelli-Grappadelli and Coston, 1991; Marini et al., 1991), leaf area
around the fruit (Kliewer and Weaver, 1971; Génard, 1992) and vigour of fruitbearing
shoots (Génard and Bruchou, 1992). Water availability determines the water
supply to the fruit, microclimatic factors such as temperature act on carbohydrate
breakdown for fruit respiration, whereas leaf area (or vigour of fruit-bearing shoots)
and possibly pests and diseases which directly or indirectly reduce carbon pools,
act on the level of carbohydrate supply to the fruit. Agricultural practices such as