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Hobson (1981), Stevens (1986), Dorais
et al.
(2001), Causse
et al.
(2007) and Causse
(2008). Cherry tomatoes have been identi-
fi ed as having the best fl avour (Hobson and
Bedford 1989), with fruits richer in acids
and sugars than large-fruited lines. In
contrast, long-shelf-life cultivars have been
described as generally less tasty than
traditional ones (Jones, 1986), with a lower
volatile content (Baldwin
et al.
, 1991).
Several studies have concerned the
qualitative and quantitative composition of
aroma volatiles in tomato varieties (Buttery
et al.
, 1987; Baldwin
et al.
, 1991; Krumbein
and Auerswald 1998; Krumbein
et al.
,
2004). Tikunov
et al.
(2005) characterized
94 genotypes for their content in 322
different compounds. A study of the in-
heritance of tomato quality traits revealed
that consumers seemed to particularly
appreciate hybrids between old and
modern lines with intermediate fi rmness
(Causse
et al.
, 2003).
In other species, several studies have
recently examined the variability within
genetic resources, focusing on common fruit
quality traits (Chessa and Nieddu, 2005;
Nunez-Palenius
et al.
, 2008; Ruiz and Egea,
2008; Ledbetter, 2009). Concerning fl avour,
diversity within germplasm collections has
rarely been investigated except in straw-
berry. Flavour compounds have been
compared between wild and cultivated
species (Aharoni
et al.
, 2004) and the
diversity of aroma was studied by Ulrich
et
al.
(2009) in wild and cultivated
Fragaria
accessions by gas chromatography/mass
spectrometry and sensory assays. In apple,
Sugimoto
et al.
(2007) revealed fruit aroma
diversity in a core collection.
identifi ed. Tomato was among the fi rst crop
for which molecular markers were used to
dissect the genetic basis of quantitative
traits into QTLs (Tanksley, 1993). Since
then, many QTLs controlling yield and fruit
quality-related traits have been mapped
(reviewed by Labate
et al.
, 2007). These
studies were all performed on progenies
derived from interspecifi c crosses between
wild tomato species and processing tomato
inbred lines. Some quality traits of interest
for processing tomato are common to fresh
market tomato (e.g. sugar content, soluble
solid content, pH, acidity and fi rmness),
and QTL locations can be compared among
the progenies. In most of the studies, QTLs
were detected, sometimes with strong
effects. A few QTLs explaining a large
fraction (20-50%) of the phenotypic vari-
ation, acting in concert with minor QTLs,
are usually detected. Most of the QTLs act
in an additive manner, but dominant and
overdominant QTLs have been detected
(Paterson
et al.
, 1988, 1991; De Vicente and
Tanksley, 1993; Semel
et al.
, 2006).
Epistasis (interaction among QTLs) is rarely
detected unless a specifi c experimental
design is used (Eshed and Zamir, 1996;
Causse
et al.
, 2007).
Several fruit quality QTL studies have
been carried out in peach using both
intraspecifi c (Dirlewanger
et al.
, 1996,
1999; Abbott
et al.
, 1998; Etienne
et al.
,
2002) and interspecifi c (Quarta
et al.
, 2000;
Quilot
et al.
, 2004) populations. Recently,
16 important QTLs controlling major fruit
quality components were mapped, includ-
ing acidity, sucrose content, fruit weight
and pH (Dirlewanger
et al.
, 2007). In apple,
Liebhard
et al.
(2003) detected QTLs for
fruit quality traits, including fruit size and
weight, fruit fl esh fi rmness, sugar content
and fruit acidity, and compared their
location to previously mapped QTLs in
apple. In apple again, a more recent study
identifi ed 74 QTLs major fruit physio-
logical traits including fruit height,
diameter, weight and stiffness, fl esh
fi rmness, rate of fl esh browning, acidity,
the soluble solid content and harvest date
(Kenis
et al.
, 2008).
14.4 QTL Mapping for Fruit Quality
Components
Identifying 'robust' quality QTLs is a
prerequisite for molecular breeding or for
their molecular characterization. Molecular
characterization of QTLs has been per-
formed to date by positional cloning, but
many Mendelian mutants have also been
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