Germination studies of clay-coated sweet pepper seeds


Sachs, M.; Cantliffe, D.J.; Nell, T.A.

Journal of the American Society for Horticultural Science 106(3): 385-389

1981


Seed germination of sweet pepper (Capsicum annuum L.) is inhibited after the seed is coated. The inhibitory effect of pellet-coating of 'Early Calwonder' pepper seed was caused by the physical properties of the coating materials. Clay coating limited part of the oxygen (02) from reaching the germinating seed and provided a mechanical barrier to protrusion of the radicle. Clay-coated pepper seed germinated satisfactorily on filter paper in a high 0 2 environment or with minimum moisture on agar. Pellet coating formulations which would provide more 0 2 to the imbibing seed would assure comparable germination of raw and coated sweet pepper seed.

J.
Amer.
Soc.
Hon.
Sci.
106(3):385-389.
1981.
Germination
Studies
of
Clay-coated
Sweet
Pepper
Seeds'
M.
Sachs,
2
D.
J.
Cantliffe,
3
and
T.
A.
Nell
3
University
of
Florida,
Gainesville,
FL
32611
Additional
index
words.
Capsicum
annuum,
pelleted
seeds,
oxygen
requirement
Abstract.
Seed
germination
of
sweet
pepper
(Capsicum
annuum
L.)
is
inhibited
after
the
seed
is
coated.
The
inhibitory
ef-
fect
of
pellet-coating
of
'Early
Calwonder'
pepper
seed
was
caused
by
the
physical
properties
of
the
coating
materials.
Clay
coating
limited
part
of
the
oxygen
(0
2
)
from
reaching
the
germinating
seed
and
provided
a
mechanical
barrier
to
protrusion
of
the
radicle.
Clay-coated
pepper
seed
germinated
satisfactorily
on
filter
paper
in
a
high
0
2
environment
or
with
minimum
moisture
on
agar.
Pellet
coating
formulations
which
would
provide
more
0
2
to
the
imbibing
seed
would
as-
sure
comparable
germination
of
raw
and
coated
sweet
pepper
seed.
Coated
seeds
are
widely
used
in
the
production
of
field,
vegeta-
ble,
and
ornamental
crops.
The
use
of
coating
is
advantageous
in
seeding
small
seeds
(tobacco,
begonia)
and
seeds
which
are
mor-
phologically
unrounded,
elongated,
or
pointed
(lettuce,
celery).
The
availability
of
coated
seeds
contributed
to
the
development
of
the
current
procedures
for
precision
seeding
of
various
crops
in
field
and
nursery
operations.
Based
on
earlier
work
(1,
13)
and
their
own
findings,
Millier
and
Scoter
(9)
concluded
that
the
inherent
problems
with
the
com-
lIteceived
for
publication
January
10,
1981.
Florida
Agricultural
Experiment
Sta-
tion
Journal
Series
No.
2860.
The
research
was
supported
in
part
by
a
grant
from
Speedling,
Inc.,
Sun
City,
Fla.
The
cost
of
publishing
this
paper
was
defrayed
in
part
by
the
payment
of
page
charges.
Under
postal
regulations,
this
paper
therefore
must
be
hereby
marked
f:dvertesement
solely
to
indicate
this
fact.
-
On
a
sabbatical
leave
from
the
Agricultural
Research
Organization,
The
Volcani
F
einer,
Ret-Dagan,
Israel.
Vegeta
Crops
and
Ornamental
Horticulture
Department,
respectively.
mercially
available
pelleted
seed,
compared
to
raw
seed,
are
re-
duction
in
the
germination
rate
and
lowering
of
total
seedling
emergence.
However,
recent
studies
showed
that
most
pelleted
seed
at
present
gives
as
good
seedling
emergence
as
does
raw
seed,
and
total
emergence
and
coefficient
of
variability
of
seed-
ling
weights
are
equal
for
coated
and
raw
seeds
(5,
1
1).
Al-
though
coated
seeds
emerge
somewhat
later
than
raw
seeds,
it
is
with
no
apparent
sacrifice
in
overall
performance
of
the
crop
test-
ed
and
does
not
reduce
yields
(3,
6,
10).
When
Bell-type
pepper
seeds
are
coated
they
do
not
germinate
properly,
and
therefore
pelleted
sweet
pepper
seeds
are
not
used
by
growers.
The
current
study
was
undertaken
to
determine
the
cause
of
the
loss
of
germinability
of
coated
sweet
peper
seeds.
Materials
and
Methods
`Early
Calwonder'
pepper
seeds
were
germinated
in
6-cm
Petri
dishes,
at
25
1°C
(2)
on
Whatman
#3
filter
paper
to
which
2
ml
of
deionized
H
2
O
was
added.
The
seeds
were
germinated
in
the
J.
Amer.
Soc.
Hort.
Sci.
106(3):385-389.
1981.
385
dark,
but
daily
counts
were
performed
in
the
laboratory
under
light.
A
seed
was
considered
as
germinated
at
the
first
sign
of
radi-
cle
protrusion.
Germination
of
clay-coated
seed
could
be
re-
corded
only
12-24
hr
after
actual
radicle
protrusion
through
the
seed
coat.
The
course
of
germination
was
plotted
graphically
and
the
values
"P"
(final
percentage),
"S"
(time
in
days
till
germina-
tion
had
reached
P16),
and
"R"
(rate
in
percent
per
day
between
P/6
and
5P/6)
were
calculated
from
the
curve
(4).
All
treatments
consisted
of
4
replicates
of
25
or
30
seeds
each.
All
experiments
were
repeated
at
least
twice.
Raw
seeds
(Asgrow
Seed
Co.
Kolamazoo,
Mich.)
were
pelleted
by
Moran
Seeds,
Inc.,
Salinas,
Calif.
All
seeds
used
in
this
study
originated
from
the
same
seed
lot.
In
experiments
in
which
the
effect
of
high-oxygen
environment
was
tested,
open
Petri
dishes
with
seeds
were
placed
in
450-m1
sealed
glass
jars.
One
layer
of
6-mm
glass
beads
and
5
ml
of
H,0
on
the
bottom
of
each
jar
ensured
high
humidity.
The
jars
were
opened
daily
to
permit
seed
counting.
The
sealed
jars
were
flushed
daily
with
10-15
volumes
of
compressed
0
2
or
com-
pressed
air
via
rubber
septums
in
the
cover
of
the
jars.
Internal
gaseous
pressure
in
the
jar
was
the
same
as
atmospheric
pressure
at
all
times,
except
for
the
flushing
periods
(6-8
min.)
In
preparations
for
scanning
electron
microscope
observations,
whole
coated
and
raw
pepper
seeds
were
mounted
on
aluminum
stubs
with
double
sided
tape
or
tube
coat
(G.
C.
Electronics
Co.,
Rockford,
Ill.),
oven
dried
at
70°C
overnight,
then
sputter-coated
with
600
rim
of
gold-palladium.
Specimens
were
viewed
in
an
Hi-
tachi
scanning
electron
microscope
(SEM),
model
S-450,
using
an
accelerating
voltage
of
20
Kv.
.
Seed
cross
sections
were
pre-
pared
by
halving
non-oven
dried
seeds
with
a
single
edge
razor
blade
and
were
viewed
immediately.
Results
and
Discussion
The
final
percentage
of
the
germination
at
25°C
of
raw
vs.
coat-
ed
seed
was
very
similar
(95
and
93%,
respectively),
whereas
the
start
of
the
germination
and
the
rate
of
germination
were
highly
different
(Fig.
I
).
Raw
seed
started
to
germinate
within
2.4
days
with
a
rate
of
46%
per
day
and
coated
seed
within
12.2
days
with
a
rate
of
8%
per
day.
When
raw
pepper
seeds
were
germinated
at
25°C
in
the
pres-
ence
of
coating
materials
(25
raw
seed
with
the
clay
material
re-
moved
from
25
coated
seed,
in
each
replicate),
germination
characteristics
were
very
similar
to
those
of
the
control
raw
seeds
(Fig.
2).
Thus,
the
coating
material
exerted
no
inhibitory
effect
on
germination.
The
rate
of
germination
of
decoated
seeds
was
slightly
lower
compared
to
raw
seeds
(41%
vs.
32%
per
day,
re-
spectively).
The
latter
differences
were
consistent
in
3
separate
experiments,
though
not
statistically
significant.
Pepper
seed
has
a
relatively
large
micropylar
cavity
(Fig.
3-A)
through
which
the
radicle
protrudes
during
germination
(Fig.
3-B,C).
After
decoat-
ing,
some
clay
still
remained
within
the
micropylar
cavity
(Fig.
3-
D).
Possibly
the
small
delay
in
germination
(compared
to
raw
seed)
was
caused
by
the
residue
of
coating
materials
remaining
in
the
cavity
situated
above
the
radicle.
The
decreased
rate
of
germination
brought
about
by
coating
pepper
seed
might
have
resulted
from
an
interference
with
0
2
dif-
fusion
through
the
coating
material
to
the
embryo.
In
the
presence
of
high
0
2
,
raw
pepper
seed
germinated
about
1
day
faster
than
seeds
which
were
germinated
in
air.
When
germinated
in
0,,
coated
seeds
germinated
as
rapidly
as
raw
seed
in
air
and
20
to
24
days
earlier
than
coated
seeds
germinated
in
air
(Fig.
4).
When
'Early
Calwonder'
seed
was
transferred
from
air
to
a
100%
0
2
environment
(on
the
4th,
8th,
or
12th
day
after
initiation
of
imbibition)
it
was
found
that
the
high
0
2
brought
about
rapid
release
of
the
"low
oxygen
inhibited
germination"
(Fig.
5).
The
high
0
2
effect
was
not
immediate,
and
germination
started
only
2
days
after
transfer
of
the
seed
from
air
to
the
high
0
2
environment.
High
0
2
treatment
exerts
its
effect
only
through
a
continuous
exposure
to
the
seed.
Short-term
exposure
(up
to
12
hr)
at
differ-
ent
times
within
the
first
10
days
of
imbibition
had
no
effect
on
germination
of
the
clay-coated
seed
(data
not
presented).
When
coated
seeds
were
imbibed
in
a
high
0
2
environment
for
I
day.
then
transferred
to
air,
germination
was
the
same
as
in
continuous
air
(Fig.
6).
After
2
days
in
high
0
2
,
before
transfer
to
air,
germi
-
nation
was
initiated
rapidly
in
approximately
40%
of
the
seeds
:
A
3-day
or
longer
exposure
to
high
0
2
resulted
in
rapid
germination
of
all
the
viable
coated
seeds
upon
transfer
to
air.
100
GE
RMIN
A
TIO
N
4
2
RAW
SEED
COATED
SEED
0
-0
12
16
24
28
DAYS
AT
25°C
0
60
z
1
7
-
4
cc
LAJ
(0
2
•—•
RAW
SEED
0-0
COATED
SEED
a---ADECOATED
SEED
RAW
SEED
+COATED
MATERIAL
4
8
12
16
20
24
28
DAYS
AT
25°C
Fig.
1.
Germination
of
raw
and
clay-coated
'Early
Calwonder
pepper
seed
at
25°C.
Fig.
2.
Germination
of
raw,
coated,
decoated,
and
raw
seed
in
the
presence
of
Coating
material
('Early
Calwonder'
pepper).
386
J.
Amer.
Soc.
Hort.
Sci.
106(3):385-389,
1981.
•ww
,„
.....
402:111011100
161
.
1101i6
Vl
U
C
I
a
iR
41.
7
.,
5seu
"
500U
Fig.
3.
Scanning
electreon
micrographs
of
'Early
Calwonder'
pepper
seed.
A)
Whole
raw
seed.
B)
Half
seed.
C)
Germinating
seed
(25°C,
4
days).
D)
Decoated
seed.
The
findings
that
coated
seed
imbibed
in
air
will
start
to
germi-
nate
only
2
days
after
transfer
to
high
0
2
(Fig.5),
that
short
expo-
sure
(up
to
12
hr)
to
high
0
2
would
not
hasten
germination
in
air,
and
that
only
3
days
(the
time
it
takes
for
raw
seed
to
start
germi-
nation
in
air)
of
continuous
exposure
to
high
0
2
would
result
in
full
germination
of
coate
d
pepper
see
d
(Fi
g.
6)
p
o
i
n
t
e
d
to
the
pos-
sibility
that
high
0
2
is
needed
to
maintain
the
overall
high
level
of
m
etabolism
in
the
ger
m
i
na
ti
ng
coate
d
see
d—
f
r
om
the
start
of
the
imbibition
to
radicle
elongation.
J.
Amer.
Soc.
Hort.
Sci.
106(3):
385-389.
1981
,
It
was
concluded
that
the
inhibitory
effect
of
clay-coating
of
pepper
seed
was
caused
by
the
physical
properties
of
the
coating
materials
which
limited
0
2
availability
to
the
seed.
The
fact
that
coated
sweet
pepper
seeds
are
inhibited
more
than
other
vegetable
seeds
may
imply
differences
in
0
2
affinity
among
various
species
during
the
germination
processes.
Two
new
coating
formulations
designed
to
provide
greater
0,
permeability
were
tested
to
determine
their
effect
on
the
germina-
tion
behavior
of
sweet
pepper
seed.
Seed
coated
with
"Moran-
387
I
P
RAW
SEED
AIR
el
,
"
OXYGENO
COATED
SEED
AIR
0-0
II
OXYGEN
0-0
GE
RM
I
N
A
TIO
N
RAN
SEED
0-4
MORAN-COAT
0-0
MORAN.COAT
5
h
--
MORAN-COAT
10
,5-6
24
28
32
36
4
8
12
16
2fJ
DAYS
AT
25'C
10
i00
.4,11
qr
CONSTANT
AIRO-0
MAY
OXYGEN
111--111
2DAYS
OXYGEN
0-0
3
DAYS
OXYGEN
111-11
$
4
DAYS
OXYGEN
6-8
SDAYS
OXYGEN
4
8
12
16
DAYS
AT
25°C
20
24
32
4
8
12
d6
20
24
28
DAYS
AT
25°C
Fig.
4.
Germination
of
raw
and
clay-coated
'Early
Calwonder'
pepper
seed
in
high
0
1
environment.
Fig.
6.
Germination
of
clay-coated
'Early
Calwonder'
pepper
seed
imbibed
for
various
durations
in
high
0,
and
then
transferred
to
air.
100
4
40
it
I
CONSTANT
OXYGEN
X
AIR
-
4
DAYS
—4
OXYGEN
12
AIR
-
8
DAYS—,
OXYGEN
rj
AIR
12
DAYS—,OXYGEN
X
CONSTANT
AIR
2
0
4
2
12
*
20
24
28
32
36
DAYS
AT
25'C
.:111.
5.
The
effect
of
high
0
2
on
germination
clay-coated
'Early
Calwonder'
seed
alter
imbibition
for
various
periods
of
time
in
air.
Coat
5"
and
"Moran-Coat
10"
formulation
resulted
in
a
consid-
erable
improvement
in
germination
when
compared
to
a
standard
"Moran-Coat"
formulation
(Fig.
7).
Both
the
start
of
the
germi-
nation
(8.2,
13.8,
and
19.8
days
respectively)
and
germination
rate
(34,
15.
and
12%
per
day,
respectively)
were
increased.
However,
all
seed
coatings
still
delayed
the
start
of
germination
when
compared
to
raw
seed.
Decreased
emergence
of
clay-coated
carrot,
lettuce,
onion,
to-
mato,
and
sugar-beet
seeds
and
sand-coated
lettuce
seed
was
re-
ported
to
he
greatest
when
soil
moisture
content
was
high
(7,
8,
9)
It
was
also
found
that
the
coating
material,
in
some
manner,
removed
0
2
from
water
as
it
passed
through
the
coat
toward
the
seed
(
12).
Thus,
if
a
balanced
air
to
water
ratio
was
created
during
germination,
inhibition
of
germination
from
the
clay
coating
might
be
eliminated.
Such
conditions
can
be
met
by
germinating
coated
seeds
on
solidified
agar.
When
clay-coated
pepper
seed
was
germinated
on
0.8%
agar,
seeds
coated
with
various
coating
formulations
("Moran-Coat,"
"Moran-Coat
5"
,
and
"Moran-
Coat
10")
had
similar
germination
patterns
(Fig.
8).
Germination
on
agar
was
more
rapid
with
these
coating
formulations
than
ger-
Fig.
7,
Germination
of
'Early
Calwonder'
pepper
seed
coated
with
different
"Moran-Coat"
formulations.
mination
on
filter
paper
(Fig.
7).
Since
coated
seed,
placed
on
agar,
did
not
germinate
as
fast
as
raw
seed
it
indicated
that
an
o
p
ti-
mum
moisture/air
balance
was
not
yet
achieved
in
the
coating
clay
material.
In
further
experiments,
it
was
established
that
exposure
to
high
0
2
overcame
the
effect
of
clay-coating
in
delaying
(by
about
24
,
hr)
germination
of
'Ithaca'
lettuce
(20°C,
light)
and
'Flora-Dade
tomato
(25°,
dark)
seed.
Yet,
the
same
treatment
did
not
enhance
the
germination
of
clay-coated
'2-14'
celery
(20°,
light)
and
'2356'
tobacco
(20°,
light)
seed
(Sachs,
unpublished
data).
Thu
s
it
can
be
generalized
that
coa
t
e
d
s
ee
d
of
species
which
react
dif-
ferently
to
high
0,
treatment
reflect
the
different
responses
of
the
various
seeds
to
the
restricted
0,
flow
through
clay-coating.
The
use
of
coating
formulations
which
allow
a
better
0,
supply
the
the
seed,
such
as
"Moran-Coat
5"
or
"Splitkote"
(a
coating
formulation
made
by
Royal
Sluis
,
Inc.,
Salinas,
Calif.)
(Sachs.,
unplished
data)
indicate
s
th
a
t
c
l
a
y-
coa
ti
ng
o
f
sweet
pepper
seed!
possible
without
the
adverse
effects
of
reduced
rate
and
lower
fi-
nal
percentage
of
germination.
388
J.
Amer.
Soc.
Hort.
Sci.
106(3).385-389.
1981.
.
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10
4
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12
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AT
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20
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in
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'Early
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