Agriculture Reference
In-Depth Information
(Seymour
et al.
, 2002; Giovannoni, 2007;
Vicente
et al.
, 2007). Fruit ripening is the
last step of a developmental programme
made up of a complex string of physio-
logical and metabolic processes including
modifi cation of pigment composition, en-
hancement of sugars, acids, aroma volatiles
and fruit softening. Internal hormonal
stimulation as well as environmental
factors such as light, temperature, water
and nutrient supply regulate ripening.
Several mutations affecting fruit ripening
and shelf-life are known. The most widely
used in tomato breeding is
ripening
inhibitor
(
rin
), which, in the heterozygous
state, enables fruits to be kept for several
weeks (Davies and Hobson, 1981). Long-
shelf-life cultivars have invaded the tomato
market, but in the 1990s their quality,
particularly their colour and fl avour, was
criticized by consumers (Jones, 1986;
McGlasson
et al.
, 1987).
melting fl esh, fruit skin colour, freestone,
fruit shape, acidity and sugar content, non-
acid fruit and fruit skin pubescence have
been mapped in apple and/or peach.
Despite the identifi cation of molecular
markers associated with these many traits,
their use in marker-assisted selection
remains limited. One of the reasons for the
lack of the extensive application of marker-
assisted selection has been the relatively
high costs of infrastructure and con-
sumables required to run it, although these
are expected to reduce as the rapidly
evolving molecular industries become able
to deliver cheaper technologies. In
peach, experiments using marker-assisted
selection have been launched within the
FruitBreedomics European project (
http://
www.fruitbreedomics.com)
for major genes
controlling fruit traits: fruit low acidity (
D
locus), fruit shape (fl at/round) (
S
locus),
glabrous fruit epidermis (peach/nectarine)
(
G
locus), fruit fl esh colour (white/yellow)
(locus
Y
) and non-melting (
F
locus).
14.7 Marker-assisted Selection for Fruit
Sensory Quality
14.8 Conclusions and Prospects
Very few experiments using marker-
assisted selection for fruit sensory quality
are available. A marker-assisted backcross
scheme was set up in tomato for intro-
ducing favourable alleles of fi ve major QTLs
regions into three tomato lines with an
ordinary taste (Lecomte
et al.
,
2004). In all
three genetic backgrounds, the introduced
regions had a favourable effect on the traits
controlled by QTLs from the donor line (a
cherry tomato), with the exception of fruit
weight. Consumer tests revealed that the
prototypes developed were signifi cantly
preferred over their corresponding re-
current parents. The QTLs appeared to be
mainly specifi c to the genetic background
(Chaïb
et al.
, 2006). About 50% of the
QTLs were stable over different years in
the recombinant inbred line population
and in the genetic background used for
QTL detection, but a lower number of
QTLs was detected in the two other genetic
backgrounds.
Regarding fruit traits, major genes or
QTLs associated for example with fi rmness,
Fruit quality is a complex character due to
the number of components involved and
because it is dependent on environmental
conditions throughout the entire process of
plant and fruit development. Genetic
variation for fruit quality is extensive,
especially if one considers the possibilities
offered by natural variation and wild
species. A few mutations have been shown
to be involved in fruit quality, particularly
in ripening, and QTL studies have revealed
a number of genomic regions involved in
the variation of quality traits. Several
genomic hot-spots for fruit quality QTLs
have been identifi ed. These clusters of
QTLs for several quality traits may permit
simultaneous marker-assisted selection for
multiple traits. Today, very few QTLs have
been identifi ed at the molecular level, but
one can expect a rapid increase in the
number of genes identifi ed in the near
future, due to systems biology approaches
combining transcriptomics, proteomics and
metabolomics studies and information
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