Natural Diversity and Genetic Control of Fruit Sensory Quality - Fruit Ripening: Physiology, Signalling and Genomics - page 241

showing alterations in the concentration of
one or more volatiles were identifi ed.
Although ten volatiles were analysed in
both studies, only three QTLs were
detected in the same regions. In both
studies, QTLs for several volatiles were
frequently in clusters. In a few cases, these
clusters corresponded to volatiles derived
from the same metabolic pathway (related
to fatty acid, carotenoid or amino acid deg-
radation), suggesting the action of a gene
within a single pathway. More frequently,
colocalizations of QTLs for volatiles
derived from various metabolic pathways
were shown, suggesting the presence of a
regulatory gene acting on several pathways.
In Solanum habrochaites introgression
lines, 30 QTLs affecting the emission of one
or more volatiles were mapped (Mathieu et
al. , 2009). In apple, Dunemann et al. (2009)
identifi ed 50 putative QTLs for a total of 27
different fruit volatiles. QTLs for volatile
compounds putatively involved in apple
aroma were found on 12 of the 17 apple
chromosomes, but they were clustered
mainly on linkage groups 2, 3 and 9.
Few studies have focused on QTL
mapping of secondary metabolites so far.
Cuevas et al. (2008) mapped QTL regulating
E -carotene composition in melon. Recently,
Huang et al. (2012) studied the genetic
basis of proanthocyanidin composition in
grape via a QTL analysis on a 191-
individual pseudo-F1 progeny. Pro-
anthocyanidins are fl avonoid polymers
determinant in food quality. The study
revealed a complex genetic control for
proanthocyanidin traits and different
genetic architectures for grape pro-
anthocyanidin composition between berry
skin and seeds.

climatic gradients (Corelli-Grappadelli and
Coston, 1991; Marini et al. , 1991) may
cause within-plant variations of quality.
Consequently, the stability of QTLs
involved in fruit quality partly depends on
the environment, as shown for sugar
concentration and fi rmness in tomato by
Chaïb et al. (2006). The importance of the
environment in the stability of QTLs for
sugar concentration has also been reported
in a QTL analysis performed under two
fruit load conditions (Prudent et al. , 2009).
In another progeny, the genotype ×
environment (G × E) interaction appeared
strong for fruit weight and aroma intensity
but not very signifi cant for fi rmness and
fruit composition (Causse et al. , 2003).
QTL detection under different saline
conditions revealed a QTL specifi c to
saline conditions (Villalta et al. , 2007),
indicating strong G × E interactions. In
melon, 27 near-isogenic lines have been
evaluated in four different locations, for
different fruit quality traits (fruit weight,
soluble solids content, maximum fruit
diameter, fruit length, fruit shape index,
ovary shape index, external colour and
fl esh colour) (Eduardo et al. , 2007). Among
these traits, soluble solids content showed
the highest G × E interaction, whereas G ×
E interactions for fruit shape and fruit
weight were low. Kenis et al. (2008)
conducted a comparison of newly detected
QTLs in apple with published QTL results
obtained using other populations (King et
al. , 2001; Liebhard et al. , 2003) and
revealed that, for the six fruit quality traits
that were measured in all populations,
only nine of a total of 45 QTLs were
common or stable across all population ×
environment combinations. Few studies
have analysed the effect of environment on
other quality traits such as fl avour, but
some clues already come from Tieman
et al. (2006a) who showed that content
in some volatile compounds of tomato
is strongly variable over years or
environments.
Although such QTL studies in different
environments allow the suggestion of clues
as to the instability of some chromosome
regions towards environmental variations,

14.5 Impact of Environment

Environmental conditions, including
cultural practices, are well-known deter-
minants of fruit growth and quality
(Heuvelink 1997; Bertin et al. , 2003;
Gautier et al. , 2008). In addition to macro-
environment variations (due to year,
location and growing conditions), micro-