Agriculture Reference
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precisely localized and then cloned by
chromosome walking (Frary et al. , 2000).
Another QTL controlling sugar con-
centration has also been cloned and
characterized (Fridman et al. , 2000). It has
been possible to study the inheritance of
the climacteric character due to the
presence of both genetically compatible
climacteric and non-climacteric types in
melon. A segregating population resulting
from a cross between a typical climacteric-
type Charentais melon ( Cucumis melo var.
cantalupensis cv. 'VĂ©drantais') and a non-
climacteric melon, Songwhan Charmi PI
161375 ( Cucumis melo var. chinensis ) has
been generated and used to study the
segregation of abscission layer (Al)
formation in the peduncle and ethylene
production. It was found that the
climacteric character was controlled by
two duplicated independent loci ( Al-3 and
Al-4 ), and the intensity of ethylene
production was controlled by at least four
QTLs localized in other genomic regions.
None of the QTLs matched known genes of
the ethylene biosynthesis or transduction
pathways.
To identify major genetic components
impacting the organoleptic quality of fruits,
a QTL approach has also been applied to
mapping a population of 144 recombinant
inbred lines derived from an intraspecifi c
cross between a cherry tomato ('Cervil') of
high organoleptic quality and an inbred
line ('Levovil') with larger fruits (Causse et
al. , 2002). These authors studied 38 traits
using a variety of physical and biochemical
assays, plus a panel of trained tasters. The
presence of QTLs for organoleptic qualities
was restricted to 14% of the genome, lying
on chromosomes 1, 2, 3, 4, 8, 9, 11 and 12.
The latter observation confi rmed and
extended previous studies using other
mapping populations. As small regions of
the genome infl uenced several traits,
Causse et al. (2002) used both QTL analysis
and local genetic mapping techniques to
determine the nature of specifi c genes
conferring pleiotropic phenotypes. Such
studies show promise for developing
molecular markers for breeding pro-
grammes and also help in the identifi cation
of candidate genes to improve the
organoleptic quality of fruits (White, 2002).
Genetic analysis of traits linked with fruit
texture have identifi ed QTLs associated
with fruit fi rmness in apple (King et al. ,
2000, 2001), tomato (Lecomte et al. , 2004;
Causse et al. , 2007), melon (Moreno et al. ,
2007) and peach (Ogundiwin et al. , 2009).
13.6 Conclusions
The genetics of fruit ripening is a complex
phenomenon controlled by several genetic
and epigenetic factors. Ripening phenom-
ena vary among species, and specifi c
biochemical changes result in modifi cation
of surface colour through the alteration of
chlorophyll, carotenoid and/or fl avonoid
accumulation, texture by alteration of cell
turgor and cell-wall structure and/or meta-
bolism, and modifi cation of sugars, acids
and volatile profi les that affect nutritional
quality, fl avour and aroma. Although fruit
species are classically defi ned physio-
logically on the basis of the presence
(climacteric) or absence (non-climacteric) of
increased respiration and synthesis of the
gaseous hormone ethylene at the onset of
ripening, fruit displaying both ripening
programmes, such as watermelon, typically
follow the same general developmental
changes. Tomato ( L. esculentum Mill.) has
emerged as the primary model system for
climacteric fruit ripening due to its simple
diploid genetics, small genome size, short
generation time, routine transformation
technology, availability of genetic and
genomic resources including mapping
populations, mapped DNA markers, exten-
sive expressed sequence tag collections and
publicly available microarrays (Tanksley et
al. , 1992; Van der Hoeven et al. , 2002;
Fatima et al. , 2008). In addition, numerous
single-gene mutations that regulate fruit
size, shape, development and ripening
combined with dramatic and readily quan-
tifi able ripening phenotypes (ethylene,
colour index, carotenoids, softening) have
enhanced the use of tomato as a model
system for climacteric ripening (Giovan-
noni, 2007). Melon ( Cucumis melo L.) is
 
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