Agriculture Reference
In-Depth Information
Table 11.10
Areas (cm
2
) of Fungal Inhibition on 1-D TLC
C. cladosporioides
Bioassay Plates for the Crude Ethanol Extract of Green Stage I, White and
Red Strawberry cv. Elsanta Fruit (100
l Spot; 0.2 ml g
−
1
FW) Run in Hexane:
Ethyl Acetate: Methanol (60:40:1 v/v/v).
Fruit development stage
μ
R
f
value
Green stage I
White
Red
0.86
—
A
~1.26
B
~1.26
B
0.44
1.96
—
—
0.37
3.85
—
—
0.13-0.00
C
13.27
1.26 (R
f
0.00)
3.85 (R
f
0.00)
Total area
19.08
2.52
5.11
A
=
No inhibition zone.
B
=
Weak antifungal activity.
C
Overlapped R
f
.
Source: Terry
et al
. (2004) with permission.
=
fruit has centred on employing heat treatment or UV-C
radiation (Tables 11.11 and 11.12). Non-ionising radiation
has potential amongst physical methods for controlling
post-harvest diseases and surface food borne bacteria.
UV-C radiation at low doses (0.25-8.0 kJ m
−2
) targets the
DNA of micro-organisms. For this reason UV-C treatment
has been used as a germicidal or mutagenic agent. In
addition to this direct germicidal activity, UV-C radiation
can modulate induced defence in harvested horticultural
produce, including soft fruit. At appropriate wavelength
and dose rates, UV-C radiation can stimulate accumulation
of stress-induced phenylpropanoids. Most published
research involving post-harvest UV-C treatments has used
the 254 nm wavelength due to its ready availability as
commercial lamps. The possibility of other wavelengths
within the UV-C band (190-280 nm) enhancing NDR
merits further investigation. In addition, effects of other
light wavelengths (e.g. the visible region of electromag-
netic spectrum) on NDR are not yet fully explored. For
instance, illumination with cool white florescent light
for 2 h reduced grey mould on strawberry cv. Dorit and
Ofra fruit (Saks
et al
. 1996). However, pulsed (30
has been around for a considerable period and there has
been no substantive commercial uptake to date.
Biological control and biologically induced resistance
The use of microbial antagonists for the control of post-
harvest fruit decay has been actively pursued. In strawberry,
grey mould development has been reduced using
Aureobasidium pullulans
(Bhatt & Vaughan 1962; Lima
et al
. 1997; Adikaram
et al
. 2002),
Trichoderma
isolates
(Pratella & Mari 1993;Tronsmo and Dennis 1997),
Pseudomonas fluorescens
,
Bacillus pumilus
(Swaldling &
Jefferies 1996),
Cryptococcus albidus
(Helbig 2002) and
Metschnikowia fructicola
(Karabulut
et al
. 2004a).
Many isolates have been shown to be as effective as stand-
ard dichlorfluanid sprays (Swaldling & Jeffries 1996;
Tronsmo & Dennis 1997), captan (Peng & Sutton 1991) or
fenhexamid (Karabulut
et al
. 2004a) in controlling grey
mould and other diseases on strawberry.
The use of avirulent or attenuated strains of either
pathogenic or saprophytic micro-organisms to induce SAR
has been relatively well researched (Terry & Joyce 2004a).
Adikaram
et al
. (2002) demonstrated that
A. pullulans
wound-inoculated green stage cv. Elsanta fruit prevented
rotting when they were subsequently inoculated with
B.
cinerea
. Similar treatment of white, pink and red-ripe stage
fruit with
A. pullulans
did not stop
B. cinerea
but did
suppress rot expansion and reduce mycelial growth.
Treatment of wound sites of green fruit with heat-killed
cells of
A. pullulans
reduced
B. cinerea
infection by 60%
s) white
light from a stroboscopic xenon lamp at a frequency of
15 Hz for 40-250 s did not reduce grey mould on strawberry
cv. Elsanta fruit despite 50% of the emitted light between
UV-C and IR being in the UV region (200-400 nm)
(Marquenie
et al
. 2003). It is, however, unlikely that UV-C
treatments will be used commercially in the near future
since the concept (Luckey 1980) and indeed the technology
μ
