Principles of Plant Genetics and Breeding

210 CHAPTER 12
Table 1 Main descriptors used to characterize each individual in each experimental site of the collaborative
INRA–NOVADI apple breeding program.
Minimum descriptors Additional descriptors
Tree Cropping, picking time Number of fruits/cluster
Fruit aspect Size, shape, attractiveness, opening calyx Ground and overcolor, % 1 and type 2 of
overcoloring, amount of russet 1 , cracking
Fruit taste Firmness, flesh quality, flavor Juiciness, sugar : acid ratio
Biotic and abiotic resistance Powdery mildew, bitter pit
1 0– 1 /4 , 1 / 4 – 1 / 2 , 1 / 2 – 3 / 4 and 3 / 4 –1.
2 Stripes, blush, blush and stripes, or stripes and blush.
inoculations, the susceptible plants are discarded. The remaining resistant trees are planted in nursery conditions at the INRA.
After 18 months, a mildew assessment is performed, and individuals that show a good level of resistance are selected. Budwoods
of scab- and mildew-resistant individuals are then sent to the nurserymen who graft them on the rootstock M9, which confers a
low vigour to the scion. The trees are planted at six nursery sites representing various French apple-cropping regions: Val de Loire
(northwest), Auvergne (central), Aquitaine (southwest), and Languedoc (southeast).
Fruit evaluation
Fruit evaluation is managed at each site at the optimum date of maturity. The description is performed by means of 20 descriptors
(Table 1): nine “minimum” descriptors are assessed for all individuals at all the sites: picking time, tree cropping, fruit size, attractiveness,
shape, opening calyx, flesh firmness, flesh quality, and flavor. Eleven additional (optional) descriptors are also recorded
(Table 1). Most of the descriptors are assessed on a 1 (low/weak/bad) to 5 (high/very good) scale, except, for example, for the
shape of the fruit (1–9), which is actually a merging assessment of the height and conicity of the fruit. All the taste traits are sensorially
assessed. Each individual is evaluated for at least 2 years in each site.
Figure 1 also illustrates the very high selection pressure applied: of the 15,000–20,000 seedlings grown in the greenhouses,
only 10 elite individuals will be finally selected. It takes about 6–7 years to reach this first level of selection. The 10 selected individuals
are then tested together with all the best worldwide selections in a national experimental network involving INRA, Ctifl
(Centre Technique Interprofessionnel des Fruits et Légumes), and regional experimental stations in various sites across France.
This long (10 years), multisite, experimental process is essential to test agronomic behavior, climatic adaptation, and consumer
acceptance of the elite selections, thus giving a guarantee to the growers before investing in a new cultivar.
Conclusion
A major problem of the commercial apple cultivars currently available is their susceptibility to the main pests and diseases, which
requires a lot of phytosanitary treatment in the orchards. After long processes of crossing and selection, apple breeders are now
releasing a new generation of cultivars. Some are already being planted significantly, for example “Goldrush” (Crosby et al.
1994), “Topaz”, and “Ariane” (Laurens et al. 2005), which combine very high standards of fruit quality with resistance to the
common strains of scab. The aim of the breeder is now to release new cultivars carrying durable resistance to scab and other
diseases and pests. For this purpose, they are developing new methodologies and tools (molecular markers) to shorten and
make more efficient the cycles of selection.
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