Mango - Crop Post-Harvest: Science and Technology - page 131

(Jacobi & Wong 1992). A hot-water brushing (HWB)
technique developed by Fallik and co-workers in Israel is
an improvement of a hot-water immersion technique in
which higher temperatures (56-64°C) can be used without
any adverse on the fruit quality (Prusky et al . 1999).
In mango, HWB treatment for 15-20 s at 56-64°C is effec-
tive in reducing the incidence of black spot caused by
Alternaria alternata (Prusky et al . 1999). The efficacy of
HWB in controlling anthracnose and stem-end rot warrants
further investigations. Heat treatments give only partial
disease control and need supplementation with fungicides.

of a commercial formulation 'Mangogreen' containing
the biocontrol agent Bacillus licheniformis , under
semi-commercial conditions in South Africa showed that
the incorporation of this agent with a hot-water dip at 45°C
for 5 min followed by a quarter strength of prochloraz dip
reduced the incidence of anthracnose and stem-end rot in
'Keitt' mangoes (Govender et al . 2005). Another example
of effective biocontrol of anthracnose in mango is the post-
harvest application of isolate 558 of Pseudomonas fluores-
cens where the bacterial antagonist reduced the anthracnose
development compared with the control (Koomen &
Jeffries 1993). The success of a commercial biocontrol for-
mulation in South Africa opens new vistas of research in
other countries also. The efficacy and stability of biocontrol
formulations under various post-harvest handling systems
deserve more attention of researchers before their release
for large scale use by the mango industry.

Combination of heat and chemicals
A combination of hot-water treatment and fungicide is the
best commercial post-harvest treatment to control post-
harvest diseases. Both rate of fungicide and duration of
exposure to hot water are lower, and efficacy is higher than
with either treatment applied separately (Arauz 2000). Hot
water and fungicides can be applied sequentially or
together. Prochloraz is the best fungicide for control of
anthracnose in mango when applied in combination with
hot water (Arauz 1995, 2000; Oosthuyse 1997; Rappel
et al . 1991; Swart & Broekhuizen 2004). The combination
of hot-water dip at 52-53°C for 3-5 min with 500 ppm
prochloraz gives excellent control of anthracnose disease
and a partial control of stem-end rot, which is the second
most important post-harvest disease (Arauz 1995; Rappel
et al . 1991). The substitution of prochloraz with benomyl
can effectively control both the diseases (Rappel et al .
1991), but the latter is now obsolete. Higher doses of hot
prochloraz at 50°C can effectively control stem-end rot and
these doses conform to the maximum residue limit of
5 ppm in the European Union (Swart & Broekhuizen 2004).
Post-harvest development of alternaria rot in mango fruit
during storage is usually prevented by a combination of
hot-water brushing with prochloraz at 225 ppm (Prusky
et al . 1999). Recently, Prusky et al . (2006) showed that
application of a combination of HWB for 15-20 s, followed
by spraying with 50 mM HCl effectively controlled
alternaria rot in stored mangoes. The acid treatment alone
was as effective as the combination of acidified prochloraz
and HWB (Prusky et al . 2006).

Other approaches
As the use of post-harvest fungicides is becoming more
and more limited, the development of new approaches
that exploit natural or induced fruit resistance represent a
feasible approach to reduce the reliance on the chemicals
for the control of post-harvest diseases. Induction of host
resistance is a good strategy to control post-harvest
diseases. The use of various chemical, physical and
biological elicitors can artificially induce host resistance
(Wilson et al . 1994). The exogenous application of salicylic
acid (SA), which is involved in the disease resistance in
plants, has been demonstrated to be effective in enhancing
the disease resistance in mango fruit (Zainuri et al . 2001;
Zeng et al . 2006). The post-harvest application of SA at
2000 ppm concentration in 'Kensington' mangoes reduced
the severity of anthracnose, but doses up to 1000 ppm were
not very effective (Zainuri et al . 2001). The vacuum
infiltration of 1 mmoll −1 SA in 'Matisu' mango also
enhanced the disease resistance against anthracnose by
increasing the activities of phenylalanine ammonia lyase
(PAL) and b -1,3-glucanase in SA-treated fruit (Zeng et al .
2006). The use of 2, 4-dichlorophenoxyacetic acid (2, 4-D)
may be helpful in strengthening the abscission zone and
thus preventing its breach by the stem-end rot pathogen.
A treatment of hot-water brushing and prochloraz followed
by 2,4-D at 75 to 175 μg ml −1 diluted in wax reduces the
stem-end rot and side rot diseases in mango by 50-70%
during prolonged storage (Kobiler et al . 2001). The
exposure of mango fruit to UV-C and infrared (IR) for
3-5 min also reduced the incidence of anthracnose, but did
not control stem-end rot and brown rot (Duvenhage 2000).
The exposure to IR radiation in controlling anthracnose

Biological control
Biological control using microbial antagonists is a relatively
new approach that can be used as a part of an integrated
post-harvest disease management strategy to reduce the use
of synthetic fungicides. The efficacy of biological control
agents can be improved if applied with the recom-
mended fungicide, used at a lower concentration. The trial