Reprinted from Tree Planters' Notes
Vol. 27, No. 2, pp 20-22
Germination of cascara seed
About This File:
This file was created by scanning the printed publication.
M. A. Radwan
Misscans identified by the software have been corrected;
however, some mistakes may remain.
Principal Plant Physiolop;ist, Paczfic Materials and Methods
Northwest Forest and Range g'peri­
ment Station, USDA, Forest Service Use of potassium gibbereliate, but not of
thiourea,
represents
a
practical
alternative
wild,
mature plants growing
Olympia,
Washington.
near
Fruit
were
to artificial stratification when spring plant­
macerated in water, and "full" seeds
ing is desirable.
were cleaned of other material by
Cascara buckthorn (Rhamnus pur­
shiana DC.), a deciduous shrub or small tree, has a natural range ex­
tending from British Columbia east to western Montana and south to central California
(4).
In addition t6 the well-known medicinal value of its bark, cascara provides protec­
tion for watersheds and food and •
The seeds.-Ripe fruit were gath­
ered in mid-August 1972 from three
cover for wildlife.
The limited information on ger­
mination and seedling production of cascara includes reports on embryo dormancy,
a pregermination treat­
ment of about 90 days of cold, moist stratification to break dormancy, fall or spring (after stratification) sow­
ing in the nursery at I-inch (2.54­
cm)
depth and shading of seedbed areas, and a maximum germination by stratified seed of only 40 percent (4, 6).
Clearly, much more informa­
tion is needed if maximum seedling production is to be achieved in the nursery and in the field. repeated
decantation.
Seeds
were
then blotted to remove moisture, air­
dried for 2 to 3 days at room tem­
perature to a moisture content of 7.8
percent, packed in a plastic bag, and
stored at 5°C until used in tests.
Stratification. -Seeds, enclosed in
nylon netting, were soaked in dis­
tilled water for 48 hours in the dark
at
room
temperature.
Seeds
were
then drained of excess water, placed
in sealed plastic vials covered with
heavy-duty aluminum foil to exclude
light, an d placed in a refrigerator at
2D
to
5DC.
Stratification
periods
(treatments) were 0, 28, 56, 84., 112,
and 140 days; and times at which
stratification was begun were sched­
uled so that all treatments were com­
pleted the same day.
Chemical treatments.
-
K-GAa
and thiourea were tested in two sep­
arate
experiments.
Solutions
used
were: 0, 100, 250, and 500 plm of
K-GAR and 0, 1, 2, and 3 percent of
'
thiourea. Test solutions were freshly
This study was designed to deter­
prepared with distilled .water, and
mine effects of different periods of seeds were soaked in the appropriate
cold,
various solution for 48 hours in the dark and
concentrations of potassium gibber­
drained as with water in the strati­
ellate
fication
moist
stratification,
(K-GAa)
and thiourea solu­
experiment.
Treated
seeds
tions, and light on germination of were not rinsed with water or al­
dormant cascara seeds. Limited pot lowed to dry before germination.
Germination tests.
-
Following
treatment (stratification, K-GAa, or
thiourea), seeds were placed in lots
of 50 in 9-cm plastic Petri dishes on
one circle of Whatman No. 3 filter
paper moistened with 7 ml of dis­
tilled water; more water was added
during tests as needed. In each of the
three
experiments,
seeds
of
each
treatment ,( six stratification periods
and four K-GA
and four thiourea
test solutions) were germinated si­
multaneously both in light and in
darkness. Seeds tested for germina­
tion in the dark were placed in the
dishes under a darkroom light with
a
green
wrapped
safelight
in
filter
and
aluminum foil.
then
There
were six 50-seed replicates for each
treatment, equally divided between
germination
tests
in
light and in
darkness.
In each experiment, dishes were
randomly transferred to an incuba­
tor programed for alternating diur­
nal temperatures of 30± 1 DC for 10
hours and . 20±1 DC for 14 hours;
preliminary
experiments
showed
such regime superior to constantly
maintained temperature. Cool-white
fluorescent light of about 900 lux
was available to seeds germinating
in light during the higher tempera­
ture.
Germinants
were counted
at
weekly intervals for 4 weeks and,
for dark germination, counts were
made under the green safelight. Pro­
trusion of radicle through the seed­
coat was used as criterio
for ger­
mination.
pregermina­
Germination percents were calcu­
tion treatments were carried out in
lated. Final, cumulative germination
seed were sown in soil at two differ­
the dark to accentuate effects of light
data of each experiment were sub­
ent depths. during germination.
jected to analysis of variance after
experiments were also conducted to evaluate
seedling
production
after In
all
experiments,
arc-sine transformation, and means
were compared according to Tukey's
test
only 3 percent in the dark. Stratifica­
tion was effective in promoting ger­
mination.
(7).
Seedling production tests.­
In
the
dark,
however,
germination remained very low
(5
Chemically treated (500 plm K-GA:l
percent or less) for up to 84 days of
and 3-percent thiourea soaks as indi­
stratification,
cated above) and untreated seeds were
creased to 55 percent after 112 days
then significantly in­
used in three four-pot tests. In each
of chilling, and reached a maximum
test, seed were sown in two I-gallon
of 88 percent after 140 days. In con­
(3.8-liter) pots at a depth of
trast, seeds exposed to light after
lis
inch
(0.3 cm) and in the other two at 1
stratification
inch
faster and more completely. Thus,
(2.54. cm) . Pots contained a
soil-vermiculite-peat
moss
mixture
always
germinated
germination in light amounted to 23
and held 100 seeds each. After they
percent after 28 days of stratifica­
were watered, pots of treated seeds
tion, increased steadily with length
were placed immediately in the incu­
of stratification period, and reached
bator used above. Remaining pots
92
were
chilled for 112 days.
transferred
to
the
incubator
percent
Table
after 16 weeks of natural stratifica­
after
2
seeds
summarizes
had
been
effects
of
tion outdoors. In each test, emerged
K-GA3 and thiourea soaks on ger­
seedlings were counted at weekly in­
mination
tervals for 6 weeks after emergence
cascara seeds. Data indicate that ef­
of
unstratified,
dormant
began.
fectiveness of these compounds as
substitutes for stratification varied
with the chemical uoed and its con­
Results
centration
Effects of
and,
more
importantly,
with light conditions during germi­
Germination
stratification
duration
nation. Thus, for K-GA:l solutions
on germination are shown in table 1.
of equal concentration, germination
Without
germination
in light was faster and higher than
was less than 20 percent in light and
germination in darkness. Maximum
stratification,
Table 1.-Cumulative germination percents of cascara seed in light and in
darkness after stratification in the dark 1
7
14
0
5
19 d
28
0
0
14
23 d
56
0
6
16
29 d
84
4
22
52
72b
80
88
91
92 a
o
germination in light than in dark­
ness and was also most effective at
the highest concentration of 3 per­
cent, producing maximum germina­
tion of 88 percent.
Highest total germination for the
most effective stratification (92 per­
cent) ,
K-GAs
thiourea
(87
(88
percent) ,
percent)
and
treatments
was essentially the same. Speed of
germination,
siderably
however,
among
varied
treatments.
con­
Thus,
at midpoint of the germination tests
(14 days), percents of total germina­
tion achieved were 96, 57, and 5 for
stratification, K-GA:J, and thiourea,
respectively.
Germinants
from
K-GA3
treat­
ments appeared as healthy and nor­
mal as those resulting from strati­
fied seeds. The thiourea germinants,
on the other hand, were relatively
weak, and many radicles had brown­
ish tips. Similar phytotoxic effects
after
treatment
by
thiourea
have
been reported with other species
(8).
Seedling Production
Average number of seedlings pro­
duced varied among treatments and
by depth of sowing. Thus,
from
21
28
In the light ------- -------------
0
140
1
Days in germination test
o
112
500 plm K-GA 3' Similarly, thiourea
promoted faster and more complete
at
Vs
inch (0.3 cm) , seedling production
Stratification period
(days)
germination of 87 percent was ob­
tained in light after treatment with
88
90
90
90 a
--------------------- In the dark --------------------
o
0
0
3 e
28
o
0
0
2 e
56
o
0
0
2 e
84
o
0
4
5 e
thiourea
treatment
(54
cent) was significantly (P
=
per­
0.05)
less than from K-GA:J (87 percent)
or stratification (80 percent)
ments.
Similar
differences
treat­
among
treatments were also evident at 1
inch
(2.54 cm)
where percents of
seedlings produced
=
33, K-GAg
tion
fore,
=
=
were:
thiourea
60, and stratifica­
40. Fewer seedlings, there­
were
consistently
produced
when seeds were sown deeper in the
112
48
52
53
55 c
soil. In addition, the greater sowing
140
72
84
86
88 a
depth always delayed seedling emer­
Percents are averages of three 50-seed replicates. In the last column, means followed
by the same letter do not differ significantly (P
=
0.05) by Tukey's test.
gence by an average of 2 days and
produced spindly plants. There were
no differences in appearance among
soak times other than those tested
seedlings resulting from the various
would
seed
also in the dark (3).
treatments
planted
at
when
the
seeds
were
(0.3
cm)
Vs-inch
depth.
effect
complete
germination
Results from the pot experiments
ing depth now recommended
(4)
duction
cascara
seeds exhibited very low germina­
also,
of
seedlings.
support
The
results,
germination
data.
tion and were considered dormant at
tive as stratification, indicating that
amount of lif!ht necessary to trigger
mancy
was
completely
stratification,
and
Dor­
broken
light
by
promoted
germination is low and, hence, not
critical
when
K-GAa-treated
seeds
higher germination until seeds had
are planted in soil. On the other
been stratified for 140 days when in­
hand, the much lower seedling pro­
fluence
duction with thiourea reflects phyto­
of
light
was
completely
eliminated. This response is similar
toxic effects on the radicles obse1'\ ed
to that of other species with dormant
during germination tests.
seeds
and
tion
light-requiring
where
dormancy
germina­
is
useful
Literature Cited
1. Baskin, J. M., and C. C. Baskin.
1971. Germination of
Treatment
Cyperus inflexlIs
l\'1uhl. Bot. Gaz. 132: 3-9.
2. Bonner, F. T.
1967. Germination of sweet gum seed in
response to light. J. For. 65: 339.
3. Evenari, M.
1965. Light and seed dormancy.
In
W.
Ruhland (ed.) Encyclopedia of plant
physiology, IS (2): 804:847. Springer­
Verlag, New York.
4. Hubbard, R. L.
1974. Rhamnlls
1. Buckthorn.
In
Seeds
of woody plants in the United States.
with K-GAa,
hut not
typically
with thiourea, represents a practical
broken hy a period of stratification
during which germination hecomes
alternative to artificial stratification
for hreaking cascara's dormancy
decreasingly sensitive to light
when spring sowing in the nursery
(2, 9).
prove
potential of different seed lots.
Thus, K-GA:I proved to he as effec­
fruit maturity
and dispersal.
should
is
As with the seeds of many woody
harvested
treatment
show that the I-inch (2.54-cm) sow­
much too deep for maximum pro­
freshly
the
for quick evaluation of germination
Discussion and Conclusions
plants,
or in the field is desirahle. Moreover,
USDA,
Agric.
Handb.
No.
450,
p.
704-108, iIIus.
5. McLemore, B. F.
1964.. Light during stratification hastens
dark-germination of loblolly pine seed.
For. Sci. 10: 348-349.
In some of these species, the light re­
quirement can
he fulfilled during
stratification (5).
data
Stratification-germination
show
a
months
lowed
requirement
for
by
full
of
4
Chemical
fol­
treatment
ahout
stratification
total
Table 2.-Cumulative germination percents of cascara seed in light and in
darkness after treatments with potassium gibberellate (K-GA ) and thiourea 1
germination
of approximately 90 percent. These re­
K-GA. (pim)
sults are not consistent with avail­
ahle
information
mum
indicating maxi­
germination
of
40
percent
ancy is prohahly due to differences
in viahility and dormancy of seeds
tested and methods used for strati­
o
o
o
3
14 e
2
12
24
36 c
250
2
16
37
56 b
500
4.
50
75
87 a
5 f
o
o
0
2
100
2
2
7
250
o
6
16
25 d
500
2
10
21
31 cd
chemical
Thus,
application
or 3 percent thiourea hroke
dormancy
chilling
was
requirement
availahle
Although
and
during
similar
500
p lm
replaced
when
o
o
0
3
12 cd
1
o
o
4
18 c
2
o
o
24
36 b
3
o
4
60
88 a
In the dark ---------------------.
light
germination.
germination
reported with other species
---------------------- In the light
the
re­
sponses to these chemicals have heen
conceivahle that
Thiourea (percent)
treatments.
K-GA
seed
of
9 ef
EXPERIMENT II
Dormant cascara seeds responded
to
28
EXPERIMENT I
---------------------. In the light ---------------------­
fication an'd germination.
favorahly
21
---------------------. In the dark
This discrep­
(4, 6).
14
100
after a recommended 3-month strati­
fication period
Days in germination test
7
(1) , it is
concentrations
or
1
o
o
o
O
le
1
o
o
o
2 e
2
o
o
o
8 d
3
o
4.
8
8 d
Percents are averages of three 50-seed replicates. In the last column, within each of
the two experiments, means followed by the same letted s) do not differ significantly
(P
=
0.05) by Tukey's test.
6. Mirov, N. T., and C. J. Kraebel.
1939. Collecting and handling seeds of
wild plants. Civ. Conserv. Corps For.
Publ. . No. 5, 42 p. U.S. Gov. Print.
Off., Washington, D.C.
7. Snedecor, G. W.
1961. Statistical methods applied to ex­
periments in agriculture and biology.
534 p. The Iowa State Univ.
Press,
Ames.
8. Tukey, H. B., and R. F. Carlson
1945. Breaking the dormancy of peach
seed by treatment with thiourea. Plant
Physiol. 20: 505-516.
9. Vaartaja, O.
1956. Photoperiodic response in germi­
nation of seed of certain trees. Can. J.
Bot. 34: 377-388.