Agriculture Reference
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(Plate 2.1; Brecht 1987). From there, ripening proceeds
through the placenta to the columella (core), with the first
visible sign of ripening being the appearance of red (or
yellow or orange) pigmentation at the distal or blossom
end of the fruit, at which point the fruit is said to be at
the  'breaker' stage. Ripening then progresses toward the
proximal (i.e. stem) end of the fruit until the entire fruit
attains its final, fully ripe colour (Plate 2.2).
Ripening of mature-green tomatoes (see Table 2.1) is
accelerated by exposure to ethylene at concentrations
>0.05 μl l −1 (Wills et  al . 2001). However, at the breaker
and  later stages of ripeness, tomato fruit are not affected
by  ethylene exposure as enough ethylene is produced
endogenously to saturate the ripening processes. Therefore,
exogenous ethylene removal is most effective at the
mature-green stage for delaying ripening. Greenhouse
tomatoes are usually harvested at breaker or later ripe-
ness  stages. Supplemental ethylene does not provide any
benefits because the ripening process will continue with
ethylene produced by the fruit. Tomatoes should not be
stored or shipped with other products that are maintained
at  lower temperature and/or lower relative humidity, and
those that are sensitive to ethylene. Mixed loads of tomatoes
with ethylene-producing fruits such as bananas and apples
can accelerate the ripening of tomatoes.
It has been suggested that ethylene acts as a rheostat
rather than as a trigger for fruit ripening, which implies
that  ethylene must be present continuously in order to
maintain transcription of the necessary genes (Theologis
1992). Therefore, interfering with ethylene biosynthesis or
perception may affect the progression of ripening at any
stage. Indeed, 1-methylcyclopropene (1-MCP), a potent
inhibitor of ethylene action, delayed colour development,
softening and ethylene production in tomato fruit har-
vested  at the mature-green, breaker and orange stages
(Hoeberichts et  al . 2002). Ripening of mature-green
tomatoes held at 20°C in air containing 0.1 μl l −1 ethylene
was substantially delayed by exposure to 1-MCP in the
concentration range 0.1-100 μl l −1 . The delay was directly
related to the concentration of 1-MCP and the exposure
time. Exposure to 5 μl l −1 1-MCP for one hour resulted
in  about a 70% increase in the time to ripen, and is a
good  potential commercial treatment (Wills & Ku 2002).
1-MCP-treated fruit showed a reduced loss of titratable
acidity during ripening, which resulted in a lower Brix:acid
ratio compared to untreated fruit. 1-MCP applied to ripe
tomatoes for two hours at 5-100 μl l −1 resulted in an
increase in post-harvest life based on fruit appearance,
with exposure to 20 μl l −1 giving a 25% increase in
post-harvest life (Wills & Ku 2002).
Figure 2.1 Tomato fruit on the vine. Photo credit:
J.K. Brecht, University of Florida.
Placenta
Radial pericarp
Locular gel
Outer
pericarp
Columella
Seeds
Skin
Figure 2.2 Anatomical structure of a tomato fruit.
Photo credit: J.K. Brecht, University of Florida.
production is generally high at the time of anthesis and for
a short time after this. It then declines to a low level (less
than 0.05 nl g −1 fruit h −1 ) during later fruit growth but
increases significantly during ripening. At the onset of the
respiratory climacteric, production is around 2-10 nl g −1
fruit h −1 (Grierson & Kader 1986). A transition of the
ethylene production feedback mechanism from negative
auto-inhibition to positive autocatalysis has been  demon-
strated in tomato fruit to occur only with ripening initiation
and progress, and is responsible for the climacteric behav-
iour of tomato fruit (Atta-Aly et al . 2000). Ripening (and
ethylene production) is initiated in mature-green tomatoes
in the locular gel coincident with the disintegration of that
tissue, the cell walls of which are  completely degraded
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