Agriculture Reference
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14.4.1 QTLs for fruit weight and shape
force, specifi c gravity and measures of cell
size and shape, and allowed the detection
of other QTLs for specifi c attributes of
texture (King
et al
., 2001).
Grandillo
et al.
(1999) summarized the
results of QTL mapping for fruit weight
obtained in 17 studies on tomato based on
progenies of various types and involving
seven wild species. Six QTLs explained
more than 20% of the phenotypic vari-
ation. A common set of 28 QTLs could be
identifi ed that frequently segregated in at
least two populations. Nevertheless, only
QTL cloning and complementation permits
determination of whether each consensus
QTL location corresponds to a single gene.
For fruit shape, Grandillo
et al.
(1999)
identifi ed a common set of 11 QTLs from
the six studies. Three major QTLs were
identifi ed,
ovate
on chromosome 2,
sun
on
chromosome 7 and
fs8.1
on chromosome 8
(van der Knaap
et al.
, 2002).
In apple, different studies have led to
the mapping of QTLs for fruit weight (King
et al.
, 2001; Liebhard
et al.
, 2003; Kenis
et
al.
, 2008) with different results in terms of
number of QTLs detected and the per-
centages of explained variability. In melon,
numerous works have described QTLs for
fruit size and shape (PĂ©rin
et al.
, 2002;
Monforte
et al.
, 2004; Zalapa
et al.
, 2007;
Paris
et al.
, 2008), which both appeared to
be under complex polygenic control.
14.4.3 QTLs for sugar and acid content
The review of Labate
et al.
(2007) in tomato
also summarized the chromosome regions
carrying QTLs for sugar content or related
traits (soluble solids; fructose, glucose or
sucrose content), based on 14 populations
involving eight different species. From
three to 19 QTLs were detected per
progeny, with a total of 95 QTLs gathered in
56 chromosomal regions. For the majority
of QTLs, the wild species alleles increased
the trait value. The large number of regions
involved suggested that many mechanisms
are responsible for increasing fruit sugar
content. The same results were obtained
for acid content (Causse
et al.
, 2002, 2004;
Fulton
et al.
, 2002), with only a few
regions common to acid and sugar content.
In contrast, frequent colocations between
QTLs for sugar content and fruit weight
(Grandillo
et al.
, 1999) with opposite
allelic effects could be detected, suggesting
pleiotropic effects of some common QTLs.
In melon, a large number of QTLs have
been detected for sugar accumulation
(Monforte
et al.
, 2004; Sinclair
et al.
, 2006;
Eduardo
et al.
, 2007; Obando-Ulloa
et al.
,
2008; Paris
et al.
, 2008; Park
et al.
, 2009),
whereas for individual organic acids more
extended research is needed (Obando
et
al.
, 2008).
14.4.2 QTLs for fruit fi rmness and texture
Labate
et al.
(2007) presented a summary of
QTLs controlling fruit fi rmness in nine
populations of tomato. Forty-six QTLs
controlling fi rmness were mapped using
seven different populations. In apple, QTLs
for fruit fi rmness evaluated by penetro-
meter measurements have been detected in
different studies (King
et al.
, 2000;
Maliepaard
et al.
, 2001; Liebhard
et al
.,
2003; Kenis
et al
., 2008). In addition, QTLs
accounting for stiffness determined by
acoustic resonance and for sensory attri-
butes of texture assessed by a trained panel
were detected by King
et al
. (2000). Other
components of texture were assessed
through mechanical measures such as
wedge fracture tests, distance at maximum
14.4.4 QTLs for volatile compounds and
secondary metabolites
QTLs for volatile compounds have been
mapped in two populations of tomato.
Saliba-Colombani
et al.
(2001) detected
QTLs for 12 volatile compounds among 18
that were quantifi ed in the progeny of a
cross involving a cherry tomato. Tieman
et
al.
(2006a) identifi ed QTLs for 23 volatiles
in a population of introgression lines
derived from
S. pennellii
. Twenty-fi ve loci
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