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Scientia
Horticulturae
135
(2012)
164–170
Contents
lists
available
at
SciVerse
ScienceDirect
Scientia
Horticulturae
journa
l
h
o
me
page:
www.elsevier.com/locate/scihorti
Review
Lenticels
on
mango
fruit:
Origin,
development,
discoloration
and
prevention
of
their
discoloration
H.
Rymbaia,
Manish
Srivastava,
R.R.
Sharmab,∗,
S.K.
Singha
aDivision
of
Fruits,
Horticultural
Technology,
Indian
Agricultural
Research
Institute,
New
Delhi
110
012,
India
bDivision
of
Post
Harvest
Technology,
Indian
Agricultural
Research
Institute,
New
Delhi
110
012,
India
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
12
September
2011
Received
in
revised
form
3
November
2011
Accepted
17
November
2011
Keywords:
Lenticel
discoloration
Lenticel
origin
Prevention
of
lenticel
discoloration
Mangifera
indica
L.
a
b
s
t
r
a
c
t
Lenticels
are
macroscopic
openings
occurring
on
the
surface
of
mango
fruit
and
are
responsible
for
gaseous
exchange
and
transpiration.
Lenticel
originates
from
the
ruptured
stomata
during
fruit
enlarge-
ment
and
growth,
reaching
their
maximum
size
at
full
maturity
of
fruit.
Distribution
of
lenticel
is
2–3
times
higher
in
the
apical
region
of
the
fruit
than
middle
or
shoulder
portion
at
all
growth
stages.
Although,
the
mechanism
of
lenticel
discoloration
(LD)
is
poorly
understood,
however
few
studies
revealed
that
it
is
due
to
several
factors
including
cultivar
differences,
movement
of
air
and
water
through
lenticel
and
mem-
brane
damage
and
liberation
of
phenolics,
as
a
consequence
of
inadequate
pre-
and
post-harvest
handling.
LD
in
mango
cultivars
is
a
serious
problem,
affecting
the
appearance
and
economic
value
of
the
fruit.
A
little
information
is
available
on
the
prevention
of
LD,
which
indicates
that
it
can
be
prevented
by
adopt-
ing
standardized
pre-
and
post-harvest
strategies
like
drying
of
orchard
soil,
fruit
bagging,
desapping
of
harvested
fruit
and
storage
in
ventilated
chamber.
©
2011
Elsevier
B.V.
All
rights
reserved.
Contents
1.
Introduction
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165
2.
Origin
and
structure
of
lenticel
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165
3.
Stages
of
lenticel
development
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165
4.
Factors
associated
with
lenticel
discoloration
(LD)
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165
4.1.
Moisture
status
at
harvest
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165
4.2.
Cultivar
differences
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166
4.3.
Postharvest
handling
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166
4.4.
Storage
temperatures.
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166
5.
Mechanism
of
lenticel
discoloration
(LD)
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166
6.
Cultivar
variations
in
lenticel
discoloration
(LD)
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167
7.
Lenticel
discoloration
(LD)
in
relation
to
phenolics
contents
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8.
Lenticel
in
relations
to
pathogen
invasion
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167
9.
Lenticel
discoloration
(LD)
and
loss
of
cosmetic
appearance
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167
10.
Lenticel
discoloration
(LD)
in
relation
to
market
value
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167
11.
Lenticel
as
essential
evil
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168
12.
Prevention
of
lenticel
discoloration
(LD)
in
mango
fruit
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12.1.
Drying
of
orchard
soil
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12.2.
Fruit
bagging
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12.3.
Use
of
insect
predators
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168
12.4.
Harvesting
method
and
desapping
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168
∗Corresponding
author.
Tel.:
+91
11
2584
8428;
fax:
+91
11
2584
2155.
E-mail
address:
rrs
fht@rediffmail.com
(R.R.
Sharma).
0304-4238/$
–
see
front
matter
©
2011
Elsevier
B.V.
All
rights
reserved.
doi:10.1016/j.scienta.2011.11.018
Author's personal copy
H.
Rymbai
et
al.
/
Scientia
Horticulturae
135
(2012)
164–170
165
12.5.
Hot
water
treatment
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168
12.6.
Storage
conditions.
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168
13.
Conclusion
and
prospects
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169
References
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169
1.
Introduction
Mango
(Mangifera
indica
L.)
is
the
most
popular
fruit
in
the
trop-
ical
regions
of
the
world
and
in
India
it
is
acknowledged
as
‘King
of
fruits’
owing
to
its
delicious
taste,
capitative
flavor,
attractive
aroma
and
commercial
value
(Sivakumar
et
al.,
2005).
Commercial
culti-
vation
of
mango
is
done
in
over
87
countries
of
the
world,
and
at
present,
it
is
cultivated
on
an
area
of
3.6
mha
with
the
production
of
31.5
million
MT
(Anonymous,
2010).
India
is
the
largest
producer
of
mango
which
produces
15.02
million
tonnes
of
mango
from
an
area
of
2.31
mha
with
a
productivity
of
6.5
MT/ha
(Anonymous,
2011).
In
India
about
30
commercially
cultivars
are
grown,
of
which
only
few
are
preferred
in
international
market.
Quality
and
appearance
are
the
important
factors
determining
the
suitability
of
cultivars
for
export
purposes.
In
most
mango
producing
countries
of
the
world,
producers
face
the
problem
of
LD
on
the
fruit
surface
(Tamjinda
et
al.,
1992),
though
cultivars
are
not
equally
susceptible.
It
is
a
serious
problem
from
the
consumer’s
preference
point
of
view,
because
the
dark
colored
spots
and
skin
blemishes
on
fruit
affect
the
cosmetic
appearance,
which
gives
an
undesirable
impression.
It
is
incorrectly
associated
with
pathogenic
infection,
consequently
depreciating
economic
value
of
fruit
(O’Hare
and
Prasad,
1992).
Thus
LD
has
become
one
factor
for
unacceptability
and
economic
loss
in
mangoes
(Bally
et
al.,
1997).
Lenticel
is
gaseous
exchange
facilitator
associated
with
fruit
peel,
or
more
correctly,
exocarp
(Du
Plooy
et
al.,
2009a)
and
have
economic
significance
in
mango
fruit
marketability
at
national
and
international
level.
An
effort
has
therefore
been
made
to
review
the
work
done
on
lenticel
in
mango.
Emphasis
has
been
given
on
origin,
structure
and
develop-
mental
stages
of
lenticel
on
mango
fruit.
Besides,
mechanisms
and
factors
associated
with
LD,
and
impact
of
discoloration
on
loss
of
cosmetic
and
market
value
of
mango
fruit
have
also
been
given
due
consideration.
2.
Origin
and
structure
of
lenticel
Although,
numerous
studies
have
been
conducted
on
differ-
ent
aspects
of
mango
fruit
development
but
few
have
been
on
anatomy
of
mango
fruit.
Like
in
other
fruit,
the
peel
of
mango
protects
the
fruit
from
several
external
factors.
Anatomical
and
histological
structures
of
plant
influence
their
adaptation
to
differ-
ent
environmental
conditions
(Polıto
et
al.,
2002).
Changes
occur
in
anatomical
structures
of
various
organs
such
as
leaf,
fruit
when
exposed
to
extremes
of
environmental
factors
(Dubey,
1994).
In
order
to
understand
the
structural,
functional
and
discoloration
of
mango
lenticel
better,
it
is
essential
to
know
their
origin
and
devel-
opment.
Dietz
et
al.
(1988)
proposed
that
lenticel
may
originate
in
one
or
two
ways
viz.;
from
preformed
stomata,
or
from
shearing
of
the
fruit
epidermis
as
a
result
of
rapid
fruit
growth.
Tamjinda
et
al.
(1992)
found
that
cells
below
the
lenticel
are
smaller
than
the
surrounding
cells
and
have
larger
intercellular
space
conforming
to
the
situation
in
stomata.
In
fruit
like
apple,
pear
and
cherries,
stretching
and
rupturing
of
the
stomata
due
to
fruit
growth
and
enlargement
can
mostly
be
the
beginning
of
lenticel
development,
though
the
lenticel
so
developed
cannot
always
be
regarded
as
‘true
lenticel’.
This
is
due
to
the
absence
of
a
distinct
phellogen
below
the
lenticel
(Wilson
et
al.,
1972).
This
was
later
confirmed
by
Bally
(1999)
in
mango
who
observed
that
ruptured
stomata
leads
to
lenticel
formation
in
mango.
Lenticel
associated
with
fruit
rind
is
considered
epidermal
structures
that
also
form
a
part
of
the
exo-
carp
(Du
Plooy
et
al.,
2009a),
due
to
their
superficial
position
and
integration
with
sub-epidermal
layers
(Du
Plooy
et
al.,
2006).
The
exocarp
is
primarily
composed
of
natural
wax,
cutin,
epidermal
layer,
sub-epidermal
tissue
and
may
also
include
structures
such
as
stomata
and
trichomes.
Therefore,
lenticel
in
mango
appeared
to
be
derived
from
stomata
(Du
Plooy
et
al.,
2009a),
the
pore
being
delimited
by
non-functional
guard
cells
and
sub-stomatal
cavity
lined
by
loosely
packed
cells,
which
probably
delimits
the
lighter
area
of
peel
visible
on
the
fruit
surface.
Prinsloo
et
al.
(2004)
con-
ducted
the
Raman
spectroscopic
observations
on
epicuticular
wax
layer
on
mango
fruit
and
confirmed
lenticel
structure.
These
loosely
packed
cells
differ
in
shape,
cell
density,
and
virtual
absence
of
plas-
tids
from
the
normal
peel
parenchyma
cells.
There
appeared
to
be
little
further
differentiation
of
the
lenticel
structure,
which
presum-
ably
acts
as
a
channel
for
water
loss
from
the
fruit
(Everett
et
al.,
2008).
3.
Stages
of
lenticel
development
Lenticel
after
their
appearance
on
fruit
peel,
gradually
inten-
sify
in
color
with
fruit
maturity.
Stomata
are
prominent
on
young
fruit
but
gradually
degenerate
in
older
fruit,
which
leads
to
the
formation
of
lenticel
(Scora
et
al.,
2002).
This
was
confirmed
by
Bally
(1999)
who
studied
the
development
of
lenticel
and
found
that
stomata
were
present
on
mango
fruit
from
the
earliest
stages
of
development.
He
reported
that
at
anthesis,
the
stomata
were
between
1
and
5
mm
in
diameter,
the
stomata
remained
intact
until
the
fruit
reach
approximately
38
g
(35
mm
wide
and
50
mm
long),
but
then
started
to
rupture,
forming
lenticels,
which
remained
on
it
till
maturity.
Khader
et
al.
(1992)
also
noticed
that
lenticel
appar-
ently
manifested
fully
up
to
60
days
after
fruit
set
with
an
average
of
3167
lenticel
per
fruit
and
remained
unaltered
thereafter.
They
also
observed
that
lenticel
distributions
per
unit
area
were
two
or
three-fold
higher
in
the
apical
region
of
fruit
than
in
the
middle
and
shoulder
regions
at
all
growth
stages
(Khader
et
al.,
1992).
Previ-
ously,
lenticel
is
considered
as
static
structures
(Wutz,
1955),
but
now
these
are
treated
as
non-static,
which
undergoes
structural
modifications
during
the
fruit
development
(Rosner
and
Kartusch,
2003;
Kalachanis
and
Psaras,
2007).
4.
Factors
associated
with
lenticel
discoloration
(LD)
LD
is
now
considered
as
a
serious
post-harvest
problem
and
rea-
son
for
LD
have
been
investigated
from
various
horticultural
and
post-harvest
management
points
of
view
(O’Hare
and
Prasad,
1992;
Willis
and
Duvenhage,
2002).
Lenticel
damage
is
typically
apparent
immediately
after
harvest
and
packing
as
small
dark
spots
about
1–5
mm
diameter
(Duvenhage,
1993).
However,
Manifestation
of
lenticel
damage
is
exacerbated
by
a
range
of
pre-
and
post-harvest
factors
that
include
occurrence
of
rain
at
harvest,
fruit
washing,
fruit
brushing
and
fruit
disinfestation
by
irradiation
(Joyce
et
al.,
2011).
These
factors
are
discussed
below.
4.1.
Moisture
status
at
harvest
In
general,
lenticel
damage
is
more
severe
and
prominent
when
fruit
are
harvested
wet
(Duvenhage,
1993).
Everett
et
al.
(2008)
observed
that
fruit
after
2
h
of
imbibing
water
became
more
Author's personal copy
166
H.
Rymbai
et
al.
/
Scientia
Horticulturae
135
(2012)
164–170
susceptible
to
lenticel
damage,
while
hydrated
fruit
after
2
h
of
los-
ing
water
were
less
susceptible
to
lenticel
damage,
because
peel
cells
in
hydrated
fruit
became
more
turgid
and
thus
susceptible
to
damage.
This
was
also
confirmed
by
(Duvenhage,
1993)
who
observed
that
lenticel
damage
was
significantly
greater
in
fruit
picked
wet
compared
to
those
picked
dry.
4.2.
Cultivar
differences
Cultivars
differ
in
their
susceptibility
to
LD.
Report
from
South
Africa
indicated
that
out
of
three
cultivars
examined
for
LD,
‘Tommy
Atkins’
and
‘Keitt’
were
more
susceptible
and
while
‘Kent’
was
least
(Oosthuyse,
1998;
Bezuidenhout
et
al.,
2003;
Bezuidenhout
and
Robbertse,
2004).
In
Australia,
LD
is
more
evident
on
‘Calypso’
than
other
cultivars,
such
as
‘Kensington
Pride’,
‘R2E2’
and
‘Honey
Gold’
(Joyce
et
al.,
2011).
The
LD
also
affects
several
mango
culti-
vars
and
occurs
in
different
mango
producing
regions
around
the
world
(Du
Plooy
et
al.,
2004).
Although,
susceptible
cultivars
often
display
variable
affliction,
discoloration
of
lenticel
on
mango
fruit
surface
is
not
unique
to
any
area
or
cultivation
practice
(Du
Plooy
et
al.,
2009a).
4.3.
Postharvest
handling
After
harvest,
inadequate
handling
or
postharvest
treatments
especially
when
sap
or
latex
is
in
contact
with
the
skin,
has
shown
to
increase
LD.
Postharvest
treatment
include
dipping
fruit
in
hot
water
at
45 ◦C
for
30
min
(Jacobi
et
al.,
2001);
at
46 ◦C
for
120
min
in
‘Tommy
Atkins’
(Mitcham
and
Yahia,
2009),
a
combination
of
hot
water
and
hot
air
(Jacobi
et
al.,
1996);
washing
fruit
in
one
or
several
disinfectants
or
soap
including
Agral®,
Cold
Power®or
Mango
Wash®(Bally
et
al.,
1997);
or
washing
fruit
in
ambient
water
(O’Hare
et
al.,
1996)
were
shown
to
increase
LD.
In
‘Tommy
Atkins’
postharvest
handling
increases
lenticel
spotting
in
a
cumu-
lative
way
and
both
red
and
black
lenticel
spotting
were
caused
principally
by
washing
fruit
in
a
calcium
hydroxide
solution
to
pre-
vent
sap
burn
(Simão
de
Assis
et
al.,
2009).
In
the
same
study
they
suggested
that
black
lenticel
spotting
occurs
principally
through
physical
processes
involving
the
entry
of
water
into
the
lenticel
and
the
subsequent
collapse
and
discoloration
of
sub-lenticellular
cells.
In
contrast,
red
lenticel
spotting
is
a
physiological
process
involving
anthocyanin
production
in
response
to
low
temperature
in
which
water
entry
to
the
lenticel
plays
a
great
role
(Simão
de
Assis
et
al.,
2009).
4.4.
Storage
temperatures
Temperature
management
is
one
of
the
most
important
factors
affecting
the
LD
and
quality
of
fresh
produce.
Storage
temperatures
below
10–12 ◦C
accelerated
the
incidence
of
red
spots
LD
(Pesis
et
al.,
2000).
Several
attempts
have
been
made
to
understand
the
aetiology
of
LD
including
effect
of
soil
type,
meteorological
factors,
nutritional
status,
water
balance,
pest
control
measures
and
water
baths
on
the
pack
line
but
none
of
these
studies
could
satisfactorily
explain
the
aetiology
of
developing
conditions
for
LD.
5.
Mechanism
of
lenticel
discoloration
(LD)
The
mechanism
by
which
discoloration
of
lenticel
is
relatively
poorly
understood
physico-chemical
mechanisms
(Joyce
et
al.,
2011).
Some
studies
have
been
conducted
to
establish
the
relation-
ship
between
LD
and
entry
of
air,
involvement
phenolics,
enzymes,
etc.
For
example,
Tamjinda
et
al.
(1992)
described
the
micromor-
phology
and
histo-chemistry
of
discolored
lenticel
on
the
cultivars
‘Namdokmai’
and
‘Falan’.
They
reported
that
the
discoloration
of
the
surrounding
tissue
was
due
to
air
and
water
entry
through
the
lenti-
cel.
The
intensifying
discoloration
on
‘Keitt’
and
‘Tommy
Atkins’
may
be
the
result
of
endomembrane
collapse
and
the
liberation
of
polyphenol
oxidase
(PPO)
activity,
which
leads
to
the
accumulation
of
phenolics
in
response
to
physiological
stress
(Beckman,
2000;
Du
Plooy
et
al.,
2004;
Bezuidenhout
et
al.,
2005)
by
the
fruit
tissue
surrounding
the
lenticel
(Grassmann
et
al.,
2002).
The
accumula-
tion
of
phenolics
into
the
cell
wall
was
observed
due
to
increase
in
electron
dense
material.
Initially
there
was
accumulation
of
simple
phenolics,
which
later
became
increasingly
coagulated,
electron-
dense
and
hardened.
Discoloration
was
therefore
observed
as
a
controlled
process
whereby
the
lenticel
cavity
and
neighboring
tis-
sues
are
encapsulated
by
cells
containing
phenolic-laden
vacuoles
and
reinforced
cell
walls
(Du
Plooy
et
al.,
2006).
Hardening
of
phe-
nolics
was
linked
to
increasingly
complex
phenolics
in
the
vacuoles
as
they
became
more
conjugated
in
advanced
stages
of
LD
(Scalet
et
al.,
1989).
There
was
a
clear
distinction
of
chronology
of
events
and
chemi-
cal
changes
on
cell
wall
of
mesophyll
cells
in
the
immediate
vicinity
of
the
lenticel
lumen
between
non-discoloration
and
discoloration
lenticel
(Du
Plooy
et
al.,
2006).
In
the
same
study,
Du
Plooy
et
al.
(2006)
observed
that
phenolic
compounds
deposited
only
in,
and
therefore
limited
to
the
tissue
in
the
vicinity
of
the
lenticel
cav-
ity.
The
close
proximity
of
resin
ducts
to
lenticel
suggests
that
these
ducts
may
act
as
the
transport
route
for
elicitors
(terpenes
as
volatile)
of
the
reactions
associated
with
cell
wall
phenolics
depo-
sition
(Diaz
et
al.,
1997;
Bezuidenhout
et
al.,
2005).
These
elicitors
may
originate
within
the
resin
duct,
with
terpenoids
being
the
most
likely
compounds
to
cause
membrane
disruption
(Lalel
et
al.,
2003).
Mobilized
terpenoids
through
resin
duct
diffuse
into
the
interstitial
fluid,
following
an
intercellular
route
towards
the
lenticel
lumen.
They
further
suggested
that
direct
contact
between
resin
ducts
and
lenticel
cavities
were
seldom
observed,
but
the
presence
of
distinct
zones
were
indicative
of
phenolic
compounds
in
the
walls
of
mes-
ophyll
cells
situated
between
these
structures.
The
electron-dense
cell
wall
material
also
increased
gradually
from
outside
of
the
cell
wall
to
the
inside,
suggesting
arrival
of
cell
wall-linking
reactants
through
the
apoplastic
route
(Du
Plooy
et
al.,
2006).
On
arrival
in
the
cell
wall,
terpenes
disintegrated
the
integrity
of
tonoplast
of
the
sub-lenticellular
cells,
causing
vacuolar
bound
phenols
to
come
into
contact
with
polyphenol
oxidase
present
in
the
cell
walls.
The
product
of
a
resultant
reaction
is
quinine
accumulating
as
a
brown-
ish
deposit
in
the
cell
walls,
visible
from
outside
as
black
marking
around
the
lenticel
(Bezuidenhout,
2005).
Progressive
chemical
changes
also
occur
in
the
vacuolar
con-
tents
of
affected
mesophyll
cells.
The
observed
red
coloration
(red
spots)
lenticel
on
the
fruit
surface
is
reported
to
be
due
to
the
pro-
duction
of
anthocyanins
(Kangatharalingam
et
al.,
2002),
flavonoids
(Dixon
and
Paiva,
1995),
and
phenylpropanoid
derivatives
(Du
Plooy
et
al.,
2009b).
The
development
of
red
pigmented
lesions
was
considered
to
be
a
plant
response
associated
with
biotic
and
abi-
otic
stress
signals
and
the
subsequent
release
of
polyphenol
oxidase
(Dixon
and
Paiva,
1995)
within
the
lenticel.
Permeation
or
infiltra-
tion
of
such
phenolics
to
the
neighboring
cells
is
restricted
by
the
reinforced
cell
walls,
thereby
isolating
the
point
of
stress
and
caus-
ing
discoloration
of
the
affected
cells.
Internal
encapsulation
of
the
lenticel
probably
forms
a
protective
barrier
between
the
lumen
and
the
proximal
tissues
to
resist
pathogen
attack
(Dixon
and
Paiva,
1995;
Beckman,
2000).
Several
factors,
both
environmental
and
physiological,
have
also
been
observed
as
triggers
or
signals
for
this
self-defense
mecha-
nism,
which
in
turn,
has
made
the
occurrence
of
LD
difficult
to
predict
and
manage
(Loveys
et
al.,
1992;
Tamjinda
et
al.,
1992;
Willis
and
Duvenhage,
2002;
Du
Plooy
et
al.,
2004).
Thus
discol-
oration
is
the
result
of
a
self-defense
strategy
to
protect
the
lenticel
and
immediate
surrounding
tissues.
Du
Plooy
et
al.
(2006)
reported
Author's personal copy
H.
Rymbai
et
al.
/
Scientia
Horticulturae
135
(2012)
164–170
167
that
no
disrupted
membranes
and
discolored
lenticel
had
con-
tinued
metabolic
reactions,
which
supports
the
idea
that
LD
is
a
manifestation
of
an
active,
stress-related
self-defense
mecha-
nism
that
fruit
underwent
before
harvest
(especially
by
wind
or
cold)
(O’Hare
et
al.,
1996;
Jacobi
and
Giles,
1997).
The
signals
for
stress-related
phenolics
to
develop,
and
the
reason
for
genotypic
variations
for
sensitivity
towards
this
signal
are
still
unclear
(Du
Plooy
et
al.,
2009b).
Besides,
the
most
sensitive
cell
zone
seems
to
be
around
lenticel
where
peel
disorder
effectively
occurs
(Gazzola
et
al.,
2004).
6.
Cultivar
variations
in
lenticel
discoloration
(LD)
At
microscopic
level,
mango
cultivars
cannot
be
distinguished
with
certainty
by
comparing
only
cuticle
thickness
and
wax
layer
architecture
(Du
Plooy
et
al.,
2009b).
Morphological
lenticel
char-
acteristics
that
can
be
attributed
to
specific
cultivars
are
size
of
the
lumen
or
cavity,
internal
organization
of
the
lenticel
and
distribu-
tion
and
density
of
the
epicuticular
wax
on
the
walls
of
the
lenticel
(Du
Plooy
et
al.,
2009a).
Du
Plooy
et
al.
(2009a)
studied
the
transverse
section
of
mango
fruit
lenticel
using
scanning
electron
microscopy
(SEM),
which
showed
that
these
superficial
differences
in
morphology
were
con-
founded
anatomically.
Among,
the
cultivars
‘Tommy
Atkins’
fruit
had
the
most
organized
and
cavernous
lenticel,
with
the
small-
est
stomata
(Du
Plooy
et
al.,
2009a).
The
epicuticular
wax
layer
on
the
cavity
walls
of
this
lenticel
was
often
initially
continuous
with
that
on
the
fructosphere.
However,
within
a
short
distance,
it
became
a
sparse
monolayer
and
disappeared
altogether.
They
further
reported
that
the
other
cultivars
‘Kent’
and
‘Keitt’
had
more
disorganized
lenticel,
with
‘Kent’
more
so
than
‘Keitt’.
Again,
in
most
lenticel,
epicuticular
wax
layers
continued
from
the
fructosphere
into
the
lenticel
lumen,
but
only
‘Kent’
had
an
abundant,
complex
layer
right
to
the
bottom
of
the
cavity.
The
wax
in
‘Keitt’
lenticel
diminished
and
disappeared
from
the
walls
of
cells
lining
the
lower
end
of
the
cavity,
although
not
as
rapidly
as
that
of
‘Tommy
Atkins’
(Du
Plooy
et
al.,
2004).
Most
of
the
varieties
are
not
equally
sus-
ceptible
to
LD
(Bally
et
al.,
1997).
In
Africa,
LD
on
‘Tommy
Atkins’
was
lesser
than
on
‘Keitt’
fruit
(Cronje,
2009).
‘Tommy
Atkins’
and
‘Keitt’
were
more
susceptible
to
LD
than
Kent
(Oosthuyse,
1998;
Bezuidenhout
et
al.,
2003;
Bezuidenhout
and
Robbertse,
2004).
In
Australia,
LD
was
more
evident
on
‘Calypso’
than
other
cultivars,
such
as
‘Kensington
Pride’,
‘R2E2’
and
‘Honey
Gold’
(Joyce
et
al.,
2011).
Although
cultivar-dependant
morphology
has
been
indicated
by
SEM,
yet
no
differences
were
visible
between
discolored
groups
for
any
of
the
cultivar.
This
indicated
that
discoloration
did
not
cause
structural
deviations
such
as
necrotic
lesions
(Du
Plooy
et
al.,
2009a).
The
visual
differences
were
therefore
expected
to
be
at
cel-
lular
level,
which
was
confirmed
by
the
studies
of
Du
Plooy
et
al.
(2009a)
who
used
transmission
electron
microscopy
(TEM)
of
the
corresponding
tissue.
The
distinct
discoloration,
they
observed
was
the
result
of
substances
deposited
in
vacuoles
and
cell
walls,
a
pos-
sible
result
of
physiological
defense
reactions
(Dixon
et
al.,
2002).
7.
Lenticel
discoloration
(LD)
in
relation
to
phenolics
contents
Lenticel
on
fruit
is
vulnerable
to
possible
infection
during
ripen-
ing
and
senescence
stage.
The
accumulation
of
phenolics
presents
a
rapid
and
efficient
blocking
and
protection
mechanism
against
such
infections
(Matern,
1994;
Wink,
1997).
Du
Plooy
et
al.
(2009b)
determined
the
phenolic
profiles
of
discolored
tissue
of
‘Tommy
Atkins’
fruit.
The
phenolics
obtained,
were
phenolic
acids,
glyco-
side
bound
phenolic
acids,
ester
bound
phenolic
acids,
and
cell
wall
bound
phenolic
acids.
This
study
revealed
that
non-discolored
lenticel
had
lower
concentrations
of
all
the
phenolic
fractions,
fol-
lowed
by
red
discolored
and
lastly,
dark
discolored
lenticel.
This
was
due
to
phenolic
acid
functionality
as
discussed
by
several
stud-
ies
(Dixon
and
Paiva,
1995;
Beckman,
2000;
Dixon
et
al.,
2002;
Grassmann
et
al.,
2002;
Zhou
et
al.,
2004).
Combined
with
the
resin
chemistry
and
terpenoid
profiles
(John
et
al.,
1999;
Bezuidenhout
and
Robbertse,
2004),
it
could
give
some
explanation
why
some
cultivars
are
more
prone
to
LD.
O’Hare
et
al.
(1999)
also
confirmed
similar
browning
on
mango
peel
due
to
artificial
induction.
8.
Lenticel
in
relations
to
pathogen
invasion
A
little
is
known
about
the
role
of
fungal
pathogens
in
lenticel
damage
on
mango
fruit.
Everett
et
al.
(2008)
in
avocado
observed
isolation
from
lenticel
showing
diffuse
browning
failed
to
yield
pathogenic
fungi,
but
saprotrophic
fungi
were
found.
In
the
same
study,
they
failed
to
detect
fungal
structures
in
lenticel
damaged
tissue.
These
results
show
that
the
cause
of
lenticel
damage
is
not
fungal,
but
there
is
a
possibility
that
saprophytic
fungi
invade
dam-
aged
lenticel
tissue,
and
then
fungal
pathogens
invade
to
cause
infection,
but
no
direct
evidence
was
found
for
this
hypothesis.
Instead,
mechanical
damage
increased
the
incidence
of
both
dis-
eases
and
lenticel
damage
(Everett
et
al.,
2008).
Lenticel
damage
symptoms
are
weakly
correlated
with
diseases
that
develop
on
the
fruit.
Instead
of
being
a
causal
relationship,
it
is
possible
that
as
both
were
worsened
by
injury
then
both
symptom
types
may
be
related
to
mechanical
damage
rather
than
to
each
other.
Thus,
damaged
lenticel
can
only
act
as
sites
for
secondary
infection
for
diseases
(Robinson
et
al.,
1993).
9.
Lenticel
discoloration
(LD)
and
loss
of
cosmetic
appearance
LD
is
evidenced
by
the
darkening
of
tissue
immediately
sur-
rounding
lenticel
on
the
skin
of
mango
fruit
(Oosthuyse,
2002).
Blemish
development
is
limited
to
the
lenticel
perimeter
and