Agriculture Reference
In-Depth Information
Table 11.12
Effect of Post-harvest UV-C Treatment on Soft Fruit Quality.
Optimum UV-C
dose (kJ m
−2
)
Cultivar
Targeted pathogen or surface bacteria
Reference
Strawberry
cv. Pajaro
0.5-1
B. cinerea
Nigro
et al
. 1998, 2000
cv. Kent
0.25
As above
Baka
et al
. 1999
cv. Elsanta
A
10-15
Enterobacteria cloacea; Escherichia
coli, Listeria monocytogenes;
Salmonella typhimurium
Terry, 2001 unpublished
cv. Elsanta
0.5-15
B. cinerea
Marquenie
et al
. 2002, 2003
cv. Seascape
4.6
As above
Pan
et al
. 2003
Boysenberry
9.2
As above
Vicente
et al
. 2004
A
=
Without calyx.
compared to controls. The partial beneficial effect of
dead cells and the very different efficacy of
A. pullulans
in
green versus riper fruit may suggest that complete arrest of
B. cinerea
in green fruit is not only due to antagonism
or nutrient competition.
A. pullulans
treatment apparently
suppressed
B. cinerea
by inducing NDR in green straw-
berry fruit. Thin-layer chromatography bioassays showed
that
A. pullulans
-treated outer skin tissue from green fruit
had greater antifungal activity against
C. cladosporioides
and
B. cinerea
than equivalent control tissue samples. Thus,
induced resistance, possibly through accumulation of phy-
toalexins, is a probable mechanism by which
A. pullulans
may inhibit
B. cinerea
rotting of green strawberry fruit.
Although biocontrol has been shown to suppress
post-harvest disease it has not generally delivered adequate
or reliable control. The true test being that very few
products are commercially used on a consistent successful
basis. The same can be argued for plant activators.
( Del-Valle
et al
. 2005) can extend shelf life of soft fruit.
However, Terry and Macnish (unpublished, 2004)
demonstrated that pre-harvest application of 50% (v/v)
ethanol on strawberry cv. Elsanta plants when the majority
of primary, secondary and tertiary flowers on the primary
truss were at green stage 1, anthesis and white bud
stages, respectively, had no effect on post-harvest disease
incidence. Foliar applications of CaCl
2
have been reported
to delay ripening and disease development in soft fruit
(Chéour
et al
. 1990, 1991; Erincik
et al
. 1998). Calcium
is believed to increase soft fruit firmness through maintain-
ing cell wall integrity (Lara
et al
. 2004). Post-harvest
applications of CaCl
2
have also been shown to maintain
fruit quality and suppress disease in strawberry (García
et al
. 1996b), raspberry (Montealegra & Valdés 1993) and
blueberry (Hanson
et al
. 1993).
GENETIC TRANSFORMATION
Traditional plant breeding programmes still dominate the
continued development of new commercially available soft
fruit cultivars. There have been reports on the biotechno-
logical improvement of strawberry (James
et al
. 1990;
Nehra
et al
. 1990; Barcelo
et al
. 1998; Jiménez Bermúdez
et al
. 2002). Despite promising work, the commercial
release of many strawberry transformants has been
hindered by the steadfast objections of some consumers to
the introduction of genetically modified foods. These
objections are no more prevalent than in the EU.
Schestibratov and Dolgov (2005) created transgenic
strawberry cv. Firework plants with enhanced resistance to
B. cinerea
via
Agrobacterium
-mediated introduction of a
pathogenesis-related protein (thaumatin II; PR-5) gene.
However, the possibility of resistance being conferred to
strawberry fruit was not tested as disease resistance was
Nonconventional strategies to suppress
post-harvest disease
The continued pressure from retailers on growers to reduce
pesticide load has encouraged researchers to investigate
nonconventional methods to control post-harvest disease
on soft fruit. Many of these treatments can be considered
to be impractical, at present, for commercial exploitation
or raise additional environmental concern (e.g. irradiation),
but at least they provide a basis for novel control strategies
to be explored further and thus should not always be
dismissed. For instance, recent work has demonstrated that
post-harvest applications of acetaldehyde (Pessis & Avissar
1990), benzoic acid derivatives (Lattanzio
et al
. 1996),
ethanol, sodium bicarbonate (Karabulut
et al
. 2004b),
chitosan (El Ghaouth
et al
. 1992) and other coatings