Agriculture Reference
In-Depth Information
Table 4.4
Summary of Post-harvest Pathogens and Associated Citrus Diseases.
Infection
site
Disease cycle and
epidemiology
Disease
Description of casual agent
Fruit symptoms
Control
References
Pre-harvest infections
Diplodia
stem-end
rot
Diplodia natalensis
Pycnidia aresubglobose to
globose, 300-700
Flower,
young
fruit
Flower,
young
fruit,
navel
Lesions appear in 7-10 days
of harvest as dark
discoloration of the rind
in the stem-end of the
fruit
Typical decay is formed at
both ends of the fruit
before involving the entire
fruit
Usually a sour, fermented
odour, and sometimes the
fruit will become black
Does not spread from
diseased to healthy fruit in
packed containers
Initial stages of infection
indistinguishable between
Diplodia
and
Phomopsis
.
Phomopsis
seldom grows
so rapidly through the
core of the fruit that decay
is exhibited at both ends
Fungus grows on dead
wood on the tree
where it produces
spores
Spores are carried in
rain water or
irrigation water to
immature fruits
Fungus becomes
established in dead
tissue of the button
surface where it
stays dormant until
harvest
Favourable
temperature and
humidity in
degreening rooms
encourages growth
of pathogen
Ethylene treatment
causes senescence
and abscission of
the button that
allow entry of the
pathogen into the
base of the fruit
Cultural practices
including removal
of dead wood
from trees
Harvest at optimum
maturity to reduce
time required for
degreening
Pre-harvest treatment
with benlate or
drenching with
TBZ before
degreening and
application of
TBZ on the
packline
Immediate cooling of
fruits after harvest
Brooks 1941
Brown & Wilson
1968
Barmore & Brown
1985
Eckert & Brown
1986
Eckert & Eaks 1989
Kucharek
et al
. 2000
Timmer
et al
. 2000
Sommer
et al
. 2002
Brown 2003d
Brown 2003e
Zhang & Swingle
2005
Syngenta 2007
μ
m in
diameter
Spores are 17-43
μ
m by
m
Young spores are hyaline,
non-septate and granular,
whilst the mature spores
are striated with one
septum
10-18
μ
Phomopsis
stem-end
rot
Diaporthe citri
(Anamorph:
Phomopsis
citri
)
Pycnidia (200-450
m) are
scattered, dark, ovoid,
thick walled and
erumpent. Alpha conidia
(2.5-4 × 5-9
μ
m) and
beta conidia (0.7-1.5 ×
20-30
μ
m) are produced.
The alpha conidia are
unicellular, hyaline and
biguttualte whilst the
beta conidia or
stylospores are filiform
and hooked and do not
germinate (predominate
in older pycnidia). On
twigs that have almost
stopped producing
pycnidia, perithecia
(125-160
μ
μ
m) develop
