Agriculture Reference
In-Depth Information
Post-harvest disorders
Physiological disorders are not serious unless kiwifruit
are harvested at an immature stage or are injured by
post-harvest dip treatments or freezing. Under these
conditions off-flavours develop and the pericarp may
become granular, water soaked, rubbery or translucent.
Exposure to ethylene and CO
2
above 8% can cause a
hard-core disorder, in which the core fails to ripen
whereas the flesh is soft and ripe (Crisosto
et al
. 2002).
White core inclusions are also related to ethylene. These
are distinct white patches of core tissue occurring within
three weeks of storage at 0°C (Cristoso
et al
. 1999).
Symptoms of internal breakdown begin as water soaking
and discolouration at the blossom end of the fruit that
spreads throughout. Eventually a 'graininess' develops
below the epidermis. Granulation of the pericarp at the
stylar end may also extend up the sides of the fruit. It is
more severe with prolonged storage and after ripening
at 20°C. Translucent patches of the pericarp have been
reported in air- and controlled atmosphere-stored fruit at
0°C after 12 weeks (Crisosto
et al
. 2002).
Pre-harvest sprays with calcium chloride slowed softening
and extended storage life by 10-12 weeks, but summer
pruning did not affect storability (Gerasopoulos &
Drogoudi 2005).
The main post-harvest problem with kiwifruits is
premature ripening, to which fungal infection contributes
by causing infected fruits to release ethylene (Brook
1991). Stem-end rot or grey mould infection by the major
pathogen,
Botrytis cinerea
Pers., occurs peri-harvest. It
gains entry through wounds, senescent flowers or direct
penetration. The fungus will grow at low temperatures and
appear after 5-12 weeks in store. Damage begins at the
stem end, progressing down the fruit with softening and
water soaking. Infection may spread to adjacent fruits in
the packing tray and become apparent as 'nesting'. Control
by pre-harvest fungicide, field hygiene (such as brushing
the fruit to remove the remains of the flowers that contain
fungal inoculum) or fungicide sprays. Several post-harvest
methods have been tested, including several day's 'curing'
at ambient temperature that may allow the fruit to develop
defences against the fungus (Sharrock & Hallett 1991),
dips in hot water at 48°C for eight minutes (Cheah
et al
.
1993b), biocontrol using yeasts or
Trichoderma
(Cheah
et al
. 1992; Cheah
et al
. 1995), fumigation with sulphur
dioxide (Cheah
et al
. 1993a), fungicide dips and natural
products (Ward
et al
. 1996). The use of volatile substances
emitted by Isabella grapes (
Vitis labrusca
L.) to control
grey mould on Hayward kiwifruit has been suggested.
Kulakiotu
et al
. (2004) found that the grape volatiles
limited the incidence of infection by reducing inoculum
density and pathogen activity.
Other rotting fungi cause ripe rots that infest through
picking wounds, leading to large, pale brown, soft lesions
reminiscent of fingerprints. The genera responsible include
Botryosphaeria
,
Colletotrichum
,
Phoma
,
Phomopsis
,
Alternaria
,
Diaporthe
and
Fusarium
(Snowdon 1990;
Cheah & Irving 1997). Control is by pre-harvest fungicide
sprays and good field hygiene. A blue mould caused by
Penicillium
sp is also found (Snowdon 1990). Infection by
Phialophora
sp may cause pitting which does not become
apparent until several months of storage have elapsed
(Testoni
et al
. 1997).
Pests cause little post-harvest damage in themselves but
are important commercially because of their quarantine
implications and associated fumigation costs. Pests of
concern are the two-spotted spider mite (
Tetranychus
urticae
Koch), armoured scale insects (
Hemiberlesia
spp,
Aspidiotus nerii
Bouché and
Quadraspidiotus perniciosus
(Comstock) ), Fuller's rose weevil (
Asynonychus cervinus
(Boheman) ) and several leafroller caterpillars, the most
important of which is the brown-headed leaf roller
Ctenopseutis obliquana
(Walker).
Future needs
New cultivars are needed, with hairless fruit being more
attractive to consumers; currently there is heavy reliance
on cv. Hayward. Premature softening remains a problem
but the mechanisms underlying this phenomenon are
not well understood. Effective pest and disease control
without pesticides is required because of pest resistance
and general consumer concern with residues. IPM has not
been fully achieved in kiwifruit (Cheah & Irving 1997).
Ethylene causes very large losses when fruit soften in
storage. The effectiveness of ethylene removal methods
using catalytic converters, potassium permanganate filters,
ozone generators or ventilation systems require careful
evaluation (Rushing 2002).
GUAVA
The common guava (
Psidium guajava
L.) is the most
important cultivated type of the 100 species of the myrtle
family (Mabberley 1997). It is indigenous to tropical
America but has spread and become a commercial crop
in Brazil, Colombia, India, Egypt, South Africa and the
West Indies (Wilson 1980).
Guavas are evergreen trees or shrubs that grow to
about 10 m in height. The fruits have a rough yellow or
green skin and are round or pear shaped. Fruits vary from
8 to 13 cm in diameter and weigh up to 700 g. They contain
