Agriculture Reference
In-Depth Information
(Ceponis & Cappellini 1985; Simttle & Miller 1988;
Kim
et al
. 1995), raspberry fruit (Joles
et al
. 1994; Haffner
et al
. 2002) and wild strawberry (
Fragaria vesca
) fruit
(Almenar
et al
. 2005).
CA has been shown to increase storage life through
decreasing respiration rate, inhibition of grey mould
development and improved retention of fruit firmness
(Table 11.7). Incorrect CA regimes increase production of
off-flavours (e.g. ethanol, acetyladehyde and ethyl acetate)
and cause berry discolouration (e.g. bleaching) and
decrease TTA (Table 11.7). However, despite extensive
research on elucidating optimum CA concentrations for
strawberry, CA and MAP are still relatively underutilised
by industry. The comparative slow uptake in CA storage
regimes for soft fruit is manifest, in part, by the tendency
for rapid product degradation after removal from CA
conditions, as reported for other fresh produce types
(Chope
et al
. 2007). In addition, the use of CA for soft fruit
is only really warranted for long-distance export (e.g. from
the United States to European Union) and is rarely used
commercially for the home-grown soft fruit market. It
follows, that further research on the use of alternative
gaseous environments is required. For instance, ozone
storage resulted in storage life extension for cranberry
(Norton
et al
. 1965), strawberry (Perez
et al
. 1999) and
blackberry (Barth
et al
. 1995). Ozone treatment can,
however, lessen fruit aroma (Perez
et al
. 1999). Other
gases, such as carbon monoxide have also been shown to
extend post-harvest life of strawberry fruit whilst not
affecting quality (El-Kazzaz
et al
. 1983). In addition,
fumigation in an anaerobic nitrogen atmosphere with
nitric oxide (NO; 5-10 μl.l
−1
) for up to 2 h at 20°C doubled
the post-harvest life of strawberry cv. Pajaro fruit subse-
quently stored at 5°C (Wills
et al
. 2000). The effects of this
treatment may be transitory in a storage environment as
NO is rapidly oxidized to NO
2
in the presence of oxygen.
Although storage in superatmospheric oxygen (80-100 %
O
2
) has been shown to extend the storage life of strawberry
cv. Camarosa fruit, it is doubtful that this treatment will be
commercially viable in the near future as it leads to
increased production of fermentation-derived metabolites
that negatively affect fruit organoleptic quality (Table 11.7;
Wszelaki & Mitcham 2000). Moreover, the potential
dangers of using flammable gas at high concentrations
are often overlooked. Incorporation of natural volatile
compounds into packaging also shows promise as a method
of extending storage life of soft fruit as many compounds
derived from strawberry or raspberry have been found to
have antifungal activity (Vaughn
et al
. 1993; Archbold
et al
. 1997; Wang, 2003).
POST-HARVEST DISEASE
Soft fruit are inherently susceptible to post-harvest decay.
Disease incidence and severity is influenced by pre- and
post-harvest environmental conditions and can be
suppressed using chemical, biological and abiotic treat-
ments. Grey mould caused by
Botrytis cinerea
(Teleomorph:
Botryotinia fuckeliana
) is the most important disease
affecting post-harvest soft fruit quality. Other significant
diseases include leak rot, mucor rot, leather rot and
anthracnose fruit rot (black spot) caused by
R. stolonifer
,
Mucor
spp,
Phytophthora cactorum
and
Colletotrichum
acutatum,
respectively (Maas 1998). A comprehensive
account of the major and minor post-harvest pathogens of
soft fruit is given by Snowdon (1990). A detailed analysis
of
Botrytis
biology and pathology is available from Elad
et al
. (2004). Strawberries are problematic with regard to
the timing of prophylactic sprays because of the long
development period of the cymose inflorescence and
sequential production of multiple trusses. Although grey
mould can be partially controlled by certain pre-harvest
cultural methods (e.g. reducing inoculum load, good
sanitation, protective cropping, drip irrigation) and
post-harvest storage techniques, the strawberry industry is
still heavily reliant on synthetic botryticides (e.g. iprodione
and pyrimethanil) applied extensively during flowering
and fruiting. There are, however, concerns over increasing
loss of efficacy of conventional fungicides due to pathogen
resistance and general unacceptability of fungicide usage
in terms of public and environmental risk (Terry & Joyce
2000). These concerns have favoured the introduction of
integrated pest management programmes and alternative
treatments for suppressing post-harvest disease incidence
and severity.
Pre-harvest infection
Strawberry fruit vary in their inherent susceptibility to
B. cinerea
according to their physiological status and geno-
type (Plate 11.5 and Table 11.8). However, no strawberry
cultivar is highly resistant to grey mould.
Botrytis cinerea
tends to infect inflorescences in the field, but extensive
fruit decay is only usually seen following harvest after the
fruit has reached and passed full harvest maturity (Powelson
1960; Bristow
et al
. 1986). Therefore,
B. cinerea
generally
remains quiescent until either physiochemical defences
and/or stimulation in the host fall or rise, respectively, to
allow invasion to continue. The inherent natural disease
resistance (NDR) of strawberry fruit declines during
fruit development and senescence, including during post-
harvest storage (Terry
et al
. 2004). Between flowering and
