Agriculture Reference
In-Depth Information
followed by sunken areas where accelerated water loss has
occurred. These injuries first appear on the berry where
some other injury has occurred, such as a harvest wound,
transit injury or breakage at the cap stem attachment.
Symptoms may also be seen around the cap stem and
slowly spread over the berry. Careful attention to SO
2
treatment procedures is necessary to minimize this damage.
Additionally, treated berries sometimes develop a
sulphurous taint (Austin
et al
. 1997).
Another problem with SO
2
fumigation of grapes is the
level of sulphite residue remaining at time of final sale.
Sulphur dioxide was once included on the 'generally
recognized as safe' (GRAS) list of chemicals, for which no
registration is required (Anon 1986). Heavy usage of
sulphites in some other foods has caused a change in
regulation, because some people are highly allergic to
sulphites. Sulphite residues in grapes are currently limited
to <10 ppm, (10 μg SO
2
/g) and there are limits on the
number of repeat SO
2
fumigations allowed, depending
upon cultivar (Anon 1989).
storage can be followed by strong rot development
(P. Westercamp, personal communication). More work in
this area is strongly recommended.
Vapour heat treatments, for example 52°C for 20 minutes
have been found to be highly effective at eradicating
Botrytis
from grape berries without causing damage to the
fruit (Lydakis & Aked 2003a, 2003b). Kock and Holz
(1991b) found that gamma irradiation could control grey
mould and Thomas
et al
. (1995) tested with some success,
combinations of hot water dip and irradiation against
various moulds. UV-C light has also been applied success-
fully to control
Botrytis
on table grapes (Nigro
et al
. 1998).
A number of researchers have found a number of bacteria,
yeasts and fungi to be effective as biocontrol agents against
grey mould and other pathogens of table grapes (Ferreira
1990; Latorre
et al
. 1997; Lima
et al
. 1999; Zahavi
et al
.
2000). Ethanol dips showed some promise for control of
Botrytis
(Gabler
et al
. 2005), and the use of ethanol vapours
(Chervin
et al
. 2005) may be developed with the pad
systems that are already in use for SO
2
delivery. The use of
pre-harvest ethanol sprays may also have positive impacts
of the postharvest shelf life (Chervin
et al
. 2009).
Interesting alternatives using edible herb extracts (Gatto
et al
. 2011) or electrolyzed oxidizing water (Guentzel
et al
.
2010) have been reported recently.
Alternatives to the use of sulphur dioxide
Considerable research has been conducted to find alterna-
tives to SO
2
treatments for grey mould control. This is
especially desirable for organic table grape growers who
are prohibited from using SO
2
(USDA 2001). Despite many
treatments showing promise in the laboratory, none is being
used routinely in a commercial setting. Limitations include
phytotoxicity and difficulties in getting good penetration
of the treatment through the grape bunches. Methods tried
include fumigation with hydrogen peroxide (Rij & Forney
1995), ozone (Sarig
et al
. 1996), chlorine (Zoffoli
et al
.
1999), chlorine dioxide (Crisosto
et al
. 1994), volatiles of
natural origin such as hexenal (Archbold
et al
. 1999),
acetaldehyde (Avissar & Pesis 1991), ethanol (Lichter
et al
. 2002) or acetic acid (Sholberg
et al
. 1996). Tripathi
and Dubey (2004) have reviewed the potential of a large
selection of natural products to control post-harvest rots.
High carbon dioxide levels have long been known to
inhibit the growth of fungi. In the last few decades,
controlled or modified atmospheres have been shown to
have promise for the control of
Botrytis
in table grapes
(Yahia
et al
. 1983, Crisosto
et al
. 1995; Retamales
et al
.
2003; Artés-Hernández
et al
. 2004). Levels of CO
2
at 15%
or above can completely suppress the growth of
Botrytis
Levels above 10% CO
2
for too long a period, however,
were found to generate off-flavours and accelerate stem
browning. Sensitivity to CO
2
was, however, dependent on
cultivar and maturity (Crisosto
et al
. 2002c, 2002d).
In some cases the return to air atmosphere at the end of
Insect quarantine treatment
Several insects that attack table grapes are of quarantine
concern and they must be eradicated prior to/or during
shipment to other countries. Novelties in sanitation or
quarantine treatments have been noticeable over the past
ten years. This has been primarily in response to the likeli-
hood that the use of the fumigant methyl bromide, which
depletes stratospheric ozone, will be phased out over the
next few years.
A number of combination treatments are being devel-
oped in order to benefit from additive and synergistic
effects. For example, an official approved protocol based
on CO
2
and SO
2
fumigation is being used in California to
export grapes to Australia, England and New Zealand.
This quarantine treatment kills black widow spiders in
packaged table grapes (Mitcham 2005). A potential area
of development for disinfestations studies is the use of
semiochemicals, chemicals that mediate interactions
between organisms (Cox 2004) and that can be used to
repel or attract and kill insects. Another area of develop-
ment are 'systems approaches': taking into account the
initial pest count in a fruit load, which can be estimated by
monitoring pests in the vineyard, to adapt the post-harvest
treatment (US EPA 2000).
