Agriculture Reference
In-Depth Information
below 5°C and above 30°C. The moulds are more severe in wet
weather when the turgid fruit is easily damaged and
conditions are ideal for the spread of the fungus.
Importance
Blue and green moulds are a major postharvest problem
where effective postharvest treatments are not used.
Moulds can be a serious problem during long-term storage
and in export shipments.
Management
•
Pick and handle fruit carefully to minimise injuries,
which are entry points for the fungus.
Clean and disinfect packing sheds, bulk bins and grading
equipment regularly. Remove rotting and discarded
fruit.
•
Use recommended registered postharvest fungicide
treatments.
•
CROTCH ROT OF HICKSON MANDARIN
■
Cause
The fungus
Diaporthe citri
(anamorph
Phomopsis citri
),
Botryosphaeria rhodina
(anamorph
Lasiodiplodia
theobromae
).
Symptoms
Crotch rot begins in the depression in the fork or junction
area between the trunk and branches of Hickson mandarin
trees. This area holds moisture and is the site of splitting
when branches are carrying a heavy crop, enabling infection
by the melanose fungus
Diaporthe citri
. The wood as well as
the bark is invaded by the fungus, sometimes for a distance
of 20 cm down the trunk and into the scaffold branches.
Gumming may occur. Frequently, the fungus extends
through the wood tissue more rapidly than it invades the
bark. The infected wood discolours, the bark cracks and, in
the advanced stage, may loosen in vertical strips. Foliage
becomes yellow, with yellow veins and premature
defoliation occurs, leaving bare, dead twigs. Yellowing of
one or more branches is often the first symptom recognised
by growers, but by this stage, the wood rotting is extensive.
Fig 6.22 Blue and green mould in harvested fruit.
spores develop to give the mould its characteristic colour.
Spores rise in clouds when affected fruit are disturbed.
Blue mould grows much more slowly than green mould,
and the blue spore masses are unable to keep pace with the
white, fungal growth. Blue mould may also produce spores
inside rotted fruit.
Source of infection and spread
Blue and green moulds are mainly postharvest diseases and
are found only in the orchard on damaged, coloured fruit.
The main source of
Penicillium
spp. are diseased fruit on the
orchard f floor and in and around the packing shed. Infection
occurs by air-borne spores penetrating through injuries to the
skin that are so small they are scarcely visible to the naked eye.
A ruptured oil gland can provide enough nutrients for spores
to germinate and infect the fruit. After packing,
Penicillium
may spread from fruit to fruit by contact, forming 'nests' of
rotting fruit. Mould growth is rapid at 20-25°C and very slow
Source of infection and spread
Spores of the fungus produced on dead twigs and branches
wash into the crotch in rain and irrigation water. The
accumulation of leaf litter in these areas ensures the
persistence of moist conditions that favour infection and
crotch rot development.
