THE EFFECT OF POLYETHYLENE GLYCOL 6000
AND OTHER CHEMICAL PREIREATMENT 0N
ASPARAGUS SEED GERMINATION

Thesis for the Degree of M. S.
MICHIGAN STATE UNIVERSITY
WAYNE BOYD COUSINS
1975

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ABSTRACT

THE EFFECT OF POLYETHYLENE GLYCOL 6000 AND OTHER CHEMICAL
PRETREATMENT ON ASPARAGUS SEED GERMINATION
By

Wayne B. Cousins

Asparagus seeds (Asparagus officinalis L.) were pretreated
in different chemical solutions to improve germination in cool sandy
soils. Soaking seeds for sixteen days in an aerated polyethylene
glycol (PEG) 6000 solution (40g/100 ml distilled water) enhanced speed
of seedling emergence. Total emergence and total germination were also
improved by soaking seeds in PEG 6000 for sixteen days. Pretreatment
in CaCl2 (lO-ZM) solution for 24 hours improved speed of germination.
When a CaCl2 (10-2M) solution soak followed sixteen days of PEG
6000 pretreatment, the greatest improvement in speed of emergence
was obtained. When seeds were soaked in PEG 6000 for sixteen days

followed by CaCl for one day, 44% emergence was obtained seventeen days

2
after sowing compared to 1% emergence for untreated seeds.

Mbisture content of asparagus seeds soaked in PEG 6000 was inversely
related to PEG 6000 concentration. It appears that PEG 6000 has an
affinity for water. When the concentration of PEG 6000 increased,
hydrogen bonding between water and the ether oxygens of PEG increased;
in turn the amount of water imbibed by the seed is reduced. It appears
that the percent water within the seed is critical for radicle emergence.

If the concentration of PEG 6000 is 40g/100 ml distilled water, the critical

percent moisture needed for radicle emergence is not obtained. This

allows the seed to be presoaked for long periods of time (16 days)

without germination or apparent detrimental effects.

THE EFFECT OF POLYETHYLENE GLYCOL 6000 AND OTHER CHEMICAL

PRETREATMENT ON ASPARAGUS SEED GERMINATION

by

Wayne Boyd Cousins

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements

for the degree of

MASTER OF SCIENCE

Department of Horticulture

1975

ACKNOWLEDGMENTS

The author wishes to express his sincere appreciation to Professor
Hugh Price for his help as advisor and Chairman of the advisory commit-
tee, and to Professors Jim Notes and Clarence Hansen for their guidance
as this work was being conducted and for their review and suggestions
in the preparation of this manuscript.

The author also wishes to thank those members of the Department
of Horticulture who made their laboratory facilities available during

this period.

ii

TABLE OF CONTENTS

Title Page
List of Tables iv
List of Figures vi
Introduction 1
Literature Review 1
Materials and Methods 7
Section I
Chemical Pretreatment of Asparagus Seeds 7

Sections II and III
Polyethylene Glycol Pretreatment of Asparagus Seeds 10

Results and Discussion 8
Section I
Chemical Pretreatment of Asparagus Seeds 8
Section II

Polyethylene Glycol Pretreatment of Asparagus Seeds 13
Section III
PEG 6000 and CaCl Pretreatment of Asparagus Seeds 25

2
Summary and Conclusion 31
List of References 35
Appendix

iii

Title

Table

Table

Table

Table

Table

Table

Table

Table

of

LIST OF TABLES

Table

Effect of chemical pretreatment of asparagus
seed for 24 hours on subsequent develOpment
after 36 days in a petri dish (50 seeds total
per replication)

Effect of polyethylene glycol (PEG) 6000 pre-
treatment of asparagus seeds on total percent
seedling emergence after 50 days (25 seeds
total per replication)

Effect of polyethylene glycol (PEG) 6000 pre-
treatment of asparagus seeds on time to 50%

of total emergence (25 seeds total per replic-
ation)

Effect of polyethylene glycol (PEG) 6000 pre-
treatment of asparagus seeds on time to 50%
of total germination (25 seeds total per
replication)

Effect of polyethylene glycol (PEG) 6000 and
calcium chloride pretreatment of asparagus seeds
on the number seedlings emerged after seven-
teen days from sowing (100 seeds total per
replication)

Effect of polyethylene glycol (PEG) 6000 and
calcium chloride pretreatment of asparagus
seeds on total percent emergence after 45
days from sowing (100 seeds total per
replication)

Effect of polyethylene glycol (PEG) 6000 and
calcium chloride pretreatment of asparagus
seeds on total percent germination after 21
days in a petri dish (100 seeds total per
replication)

Effect of cold treatment of asparagus seeds
on subsequent seedling development after

36 days in a petri dish (50 seeds total per
replication)

iv

16

l7

18

26

27

28

39

Title of Table

Table 9.

Table 10.

Table 11.

Effect of cold storage on asparagus seeds

later soaked in gibberellic acid 4/7 on

subsequent seedling development after 40

days in a petri dish (50 seeds total per
replication) 40

Effect of Ethephon pretreatment of asp-

aragus seeds on subsequent seedling deve-

lopment after 40 days in a petri dish (50

seed total per replication) 41

Effect of concentrated H SO scarification
of asparagus seeds on germination (33 seeds
per replication) 42

LIST OF FIGURES

Title of Figure

Figure 1. Effect of pretreating asparagus seeds in
polyethylene glycol (PEG) 6000 on percent
moisture within the seed (10 seeds total
per replication)

Figure 2. Effect of polyethylene glycol (PEG) 6000
pretreatment for sixteen days on asparagus
seed germination (25 seeds total per
replication)

Figure 3. Effect of polyethylene glycol (PEG) 6000
pretreatment for sixteen days on asparagus
seedling emergence (25 seeds total per
replication)

Figure 4. Effect of pretreating asparagus seeds in 40g
of polyethylene glycol (PEG) 6000 per 100 ml
of water for sixteen days and/or one day
of soaking in calcium chloride on the
emergence rate (100 seeds total per
replication)

vi

INTRODUCTION

In today's world of mechanization, producing crops efficiently
is one of the main goals of a grower. Direct seeding has become a very
important practice to increase efficiency for the grower. Compared to
transplanting, direct seeding provides more disease free seedlings,
more flexibility in planting schedules and plant population and greater
speed in planting as well as lower establishment cost. (38).

In Michigan 17,000 acres of asparagus (Asparagus officinalis L.)

 

were harvested in 1974 producing 12,750 tons. This is an increase of
2,500 acres harvested over 1972. The market value of asparagus harvested
in Michigan in 1974 was $8.6 million or greater than $500 an acre.

The conventional method of establishing a field of asparagus is
with one or two year old crowns planted in the bottom of a seven to
eight inch trench. However, planting crowns is a very expensive operation
costing approximately $258 an acre (2). Establishing an asparagus field
by direct seeding has presented one major problem. It takes from three
to six weeks for the seedlings to emerge from cool, sandy soils (7).
When asparagus seeds are planted in the bottom of a six inch v-shaped
trench, erosion of the sides of the trench often occurs prior to seedling
emergence and covers the seed with four to six inches of soil. The
seeds may never emerge from this depth resulting in a poor stand which
is uneconomical to maintain.

Asparagus spear diameter is affected by crown depth. If asparagus
is direct seeded at .75 to 1.0 inch depth and not lowered, the average
weight per spear is 40 to 50 percent less than the spear weight from

1

asparagus established by crowns at the same time (29). This reduction
is not desirable because small spear size reduces the value and quality
of the crop. To solve this problem, Michigan State University has
deve10ped a Lister-transplanter (l) to lower direct seeded asparagus
crowns to a desired depth. This machine lifts a ribbon of soil containing
the crowns onto a conveyor belt. While the crowns are on the conveyor,
a middle buster forms a trench nine to ten inches deep into which the
ribbon of soil is lowered. Using the Lister—transplanter method for
lowering crowns, the total cost of establishing an acre of asparagus is
$174 (2). However, obtaining an adequate stand of field seedlings is
still an important factor.

Early work by Borthwick (7) on asparagus germination showed that
if seeds were soaked in water for 110 hours at 30°C, then germinated at
room temperature, 64% of the seeds had germinated after two days while
none of the non-soaked seeds had germinated. Asparagus seeds showed no
signs of dormancy and would germinate readily after harvesting. Borthwick
also showed that the optimum germination temperature for asparagus seeds
was 86°F.

Komoti (17) showed that placing asparagus seeds in a 0 to 5°C cold
storage for two months resulted in better germination than was obtained
from seeds that were not cold treated. Germination was also improved by
scarifing the seeds in concentrated HZSOAfor ten minutes. After four days
the acid treated seeds obtained 84% germination while only 5% of the
untreated seeds germinated. In contrast to Borthwick, Komoti reports that
there was dormancy present in asparagus seeds just after harvest and

that the dormancy was intensified by drying.

Growth regulators have been added to seeds to improve germination.
Bradbeer gt §l° (8) showed that treating hazel nut seeds with gibberellic
acid increased germination by substituting for stratification which is
normally required for germination. In the case of hazel seeds abscisic
acid was the chemical retarding germination. Treatment with gibberellic

acid and/or stratification reduced the concentration of abscisic acid

or gibberellic acid synthesis was increased. Ketring §£_al, (16) found
that gibberellic acid treatment of peanut seeds increased the production
of ethylene gas and increased germination. Toole 2; a1. (37) reported
that an ethylene treatment for peanut seeds increased germination;
however, when ethylene was combined with carbon dioxide the best germination
rate was obtained. Work done on tomato seeds (32) also showed an improvement
in germination rate with the addition of ethylene and carbon dioxide.
Lettuce (3) and rape (35) were some of the other crops which ethylene
has increased germination.

'Hardening' has improved germination. It is a process of soaking
the seeds for 24 hours then drying the seeds for 24 hours. This cycle
may be repeated three or four times. Austin gt El! (4) and Hegarty (9)
reported that carrot seeds which were hardened had a higher rate of
germination than did the untreated seeds. Hegarty also found that two
of five cultivars of corn seed tested showed a significant improvement
for hardened seeds compared to untreated seeds. Hegarty also reported
that carrot seeds hardened in a solution of KZHPoainstead of water improved
in germination rate.

Inorganic salts have been used to improve seed germination. Oyer

33 El- (28) found that soaking tomato seeds in solutions of KNO3and

K3P041mproved germination at suboptimal temperatures. Other work done
with KNO3(10) showed an increase in germination for pigweed, yellow
foxtail, timothy and barnyardgrass. Work done on pollen (6,19) showed
that pretreating the spores with calcium increased germination.

Water and polyethylene glycol 6000 have been used to increase
germination. Bleak gt 31. (5) showed that emergence of several forage
grasses was greatly improved by pretreatment for 30 to 60 hours in 16°C
water. Heydecker g£_§1, (11) reported that presoaking onion, carrot,
beet and celery seeds with polyethylene glycol (PEG) 6000 greatly improved
the rate of germination. In the case of onion, seeds pretreatment for
23 days in 29g of PEG 6000 per 100 ml of distilled water, the treated
seeds germinated in 20 hours at 10°C compared to 9.3 days for untreated
seeds. These results were obtained by allowing seeds to air dry for
one hour after their removal from the PEG 6000 solution. However, if
the same onion seeds were allowed to air dry fully then the pretreated
seeds required three days to germinate which was 6.3 days sooner than
non-soaked seeds. Heydecker gt a1. (11) feels that PEG 6000 places an
osmotic suction on the seed which counteracts the suction of the imbibing
seed. In other words, if the osmotic potential of the solution was too
weak then the seeds would germinate in the solution; however, if the
osmotic potential was too high then insufficient water is absorbed and
the seed's metabolism is not stimulated.

One advantage for soaking seeds in PEG 6000 is that the molecule is
very large and cannot pass into the plant cells (11,13,15,21,24,25,36).

This permits prolonged pretreatment of seeds without chemical harm.

However, the larger PEG molecules such as 6000 and 20,000 contain ions
of aluminum and magnesium which may be toxic to the plants (13,20,21).
Janes (13) reported that pepper roots placed in a solution from one
particular lot of PEG 4000 were brown and appeared flaccid after 24 hours.
If the same solution were passed through a column of standard Bantam
demineralizing resin, the roots grown in the solution showed no signs of
injury after seven days. Studies have been conducted where no toxic
effects develop when the plants are grown in unpurified solutions of PEG
6000 and PEG 20,000 (15,25,26). Mexal 25 31. (24) reported that osmotic
potentials of -12 bars for PEG 4000 and -7 bars for PEG 6000 decreased
the oxygen availability severely. This may be the source of some toxic
effects when seeds are soaked in PEG 6000 and not the aluminum and
magnesium ions (12).

Another problem is that the osmotic potential for polyethylene glycol
changes inversely with temperature. Taking this into account Michel
ggugl. (27) has developed an equation to calculate the osmotic
potential. The equation is as follows:

Osmotic potentia1= -(1.18x10‘2)C-(1.18x10-4)CZ+(2.67x10_4)CT
+(8.39x10-7)C2T

where,

0
II

concentration of PEG in g/kg water

T8 temperature in degrees C
The changes in the osmotic potential as a function of temperature are
speculated to be caused by hydrogen bonding between PEG and water, and
as the temperature increases the hydrogen bonding is reduced producing

a lower osmotic concentration.

Work done on pea seeds (22), grown in a -506 joules/kg solution
of PEG 6000 showed a decrease in germination rate. Similar results
(14) were obtained for lettuce, sunflower and citrus seeds grown in
-l.1, -2.3 and -4.1 bars of PEG 6000 solution.

Even though very little work has been published dealing with
pretreating asparagus seeds to improve germination rate, the work done
with other seeds is enormous. However, most of the work has been in the
area of dormancy breaking and light substitution. Still there are many
ideas and treatments which have been tried on other crops which can be
performed on asparagus to determine if the seeds will germinate faster.
This thesis reports results of research conducted to achieve faster

germination of asparagus seeds in cool soils.

MATERIALS AND METHODS

Section I

Chemical pretreatment of asparagus seeds

Asparagus officinalis L. (cv. Mary Washington) seeds were soaked

 

in different chemical solutions for 24 hours. The four treatments were
potassium nitrate (KNOB), calcium chloride (CaClz), gibberellic acid
(GA 4/7) and Alar. Seeds that were not soaked before germination were
the control. After 24 hours of soaking, the seeds were removed and
allowed to air dry for 24 hours. Fifty seeds from each treatment were
placed in a lO—cm petri dish which contained one 9-cm'Whatman #1 filter
paper. Approximately five milliliters of distilled water was added to
the seeds in each petri dish. The petri dishes were placed in a 68°F
growth chambef and kept in total darkness. To assure an adequate water
supply for the seeds, the dishes were checked daily. Each treatment was
replicated five times. After 36 days the seeds were removed and fresh

weight, shoot length and germination count were determined.

RESULTS AND DISCUSSION

Section I

Chemical pretreatment of aspargggs seeds

Seedlings from asparagus seeds presoaked in CaCl2 at the highest
concentration (lO-ZM) and seeds soaked in an intermediate concentration
Alar (lo-3M) were greater in both fresh weight and shoot length than
seedlings from seeds that were not pretreated (Table 1). Seedlings from
seeds soaked in the highest concentration of Alar (lO-ZM) showed a marked
improvement over untreated seeds in average shoot length; however, there
was no significant difference in fresh weight compared to seedlings from
untreated seeds. The rest of the treatments were not significantly
different from untreated seeds except seeds soaked in the lowest
concentration of Alar (lo-4M) which showed a significant decline in fresh
weight. Total germination was not significantly different even though
it varied from a low of 22.4 for seeds soaked in 10’3M of CaCl

2

of 32.4 for seeds soaked in 10- M of CaClz.

2 to a high

Table 1. Effect of chemical pretreatment of asparagus seed for 24
hours on subsequent seedling development after 36 days
in a petri dish (50 seed total per replication)

 

Chemical Conc. Fresh Weight Average Shoot Number of
(M) (gm) Length (mm) Seeds Germinated
-2 *
KNO3 10 0.38 ab 12.1 a 25.8 a
KN03 10"3 0.33 ab 10.8 a 22.6 a
0a012 10‘2 0.92 d 31.2 c 32.4 a
CaCl2 10"3 0.29 ab 12.2 a 22.4 a
GA 4/7 10'3 0.55 be 14.5 a 27.8 a
GA 4/7 10‘4 0.35 ab 15.5 a 24.0 a-
Alar 10‘2 0.77 cd 24.1 b 29.0 a
Alar 10'3 0.93 d 26.0 be 29.0 a
Alar 10’4 0.21 a 8.4 a 28.0 a
Alar 10"3
and _4 0.35 ab 11.4 a 26.2 a
GA 4/7 10
Not Soaked (Control) 0.55 bc 14.3 a 30.6 a

 

*
Means within columns followed by common letters are not significantly
different at the 5% level (Duncan's Multiple Range Test).

MATERIALS AND METHODS

Section II and III

Polyethylene glycol pretreatment of asparagus seeds

Asparaggs officinalis L. (cv. Mary Washington) seeds were presoaked

 

in nine concentrations of polyethylene glycol (PEG) 6000. Flasks containing
150 ml of the PEG solution and 1000 seeds were aerated using compressed
air passed through an aeration stone. The flow of air to each flask
was kept constant by a clamp at the head of the line running to each
flask. The air flow was adjusted so that small air bubbles could be
seen saturating the solution. Water was added to flasks each day to
replace evaporation loss. Solutions were thereby maintained at the
desired concentration. In section II samples were taken periodically
during the 30 days of pretreatment. At each sampling 60 seeds were
removed from each of four replicated flasks. 0f the 60 seeds removed
25 seeds were used in a germination test, 25 seeds were used in an
emergence test and the final 10 seeds were used to determine percent
moisture. Seeds remaining in the flasks were placed in a fresh solution
of PEG 6000. The seeds used for the germination and emergence studies
were rinsed in distilled water to remove the excess PEG 6000 and allowed
to air dry for 24 hours before being planted. The seeds for the percent
moisture determinations were also rinsed with water, blotted dry and
placed in crucibles and weighed.

The seeds used for the emergence study were planted l/2 inch deep

in 2 parts loam and a 1 part sand soil mix. The soil was sterilized

10

11

before being placed in a 20xl4x3 inch flat in a 65°F greenhouse. No
fertilizer was added to the soil. The flats were watered twice a week

and counts were made on the emerged seedlings when the shoots were 1/2 inch
tall. Counts were made twice weekly for three weeks. Fifty days after
sowing the shoots were counted and cut at the soil surface for fresh

and dry weight determinations. The shoots were placed in a 150°F oven

for 48 hours, removed, cooled for 30 mdnutes and weighed to determine

dry weight.

For the germination test petri dishes were covered with Parafilm
with a 1 cm2 hole cut in the Parafilm on one side of the dish (18). Two
pieces of 7-cm diameter Whatman #2 filter paper were placed on top of
the Parafilm.with a small portion of the filter paper out and placed
through the hole to act as a wick. Twenty five ml of distilled water
was placed in the petri dish and 25 seeds were placed on top of the
filter paper and covered with the petri dish lid. This method allowed
the seeds to be in contact with water but not submerged. The dishes
were then placed in a 18°C incubator. Counts of the germinated seeds
started seven days after the seeds were placed in the petri dish and
continued two to three times a week until 17 of the 25 seeds had germinated
or 33 days had passed whichever came first. Seeds were counted as
germinated if the radicle was visible.

To determine percent moisture content (30), ten seeds per replication
were placed in a crucible and weighed following their removal from the
different PEG 6000 pretreatments. They were then placed in a 130°C oven
for 60 minutes after which they were removed and allowed to air cool for

30 minutes before they were weighed.

12

In section III the PEG 6000 concentration giving the greatest
increase in speed of seedling emergence was combined with the CaCl2
presoaking described in section I. The asparagus seeds were presoaked
in a 40 gram/100 ml solution of PEG 6000 utilizing the aeration system
described previously. Ten days after initiation of the presoaking
treatments, the PEG 6000 solution in one-half of the aerated flasks
was replaced with fresh solution; the remaining flasks retained the
original PEG 6000 solution. At l6, l9, and 22 days after the presoaking
treatments were initiated, samples of 600 seeds from each flask.were
removed. Of the 600 seeds, 100 seeds were used for a germination test
and an additional 100 seeds were used for an emergence test. The
remaining 400 seeds were split into two lots and soaked for an additional
day in two concentrations of CaCl2 before being prepared for a germination
and emergence test. Four hundred additional seeds (not presoaked in
PEG 6000) were also split in two lots and soaked in the different
concentrations of CaClZ. Six replications were used per treatment.

The experiment in section III was terminated after 45 days for the

emergence test and after 21 days for the germination test.

RESULTS AND DISCUSSION

Section II

Polyethylene glycol pretreatment of asparagus seeds

There was no significant difference in total seedling emergence
(Table 2) for any treatment through the 13th day. After sixteen days of
soaking the seeds soaked in 20 and 40 grams of PEG 6000, solutions had a
67 and 73% seedling stand respectively, while the untreated seeds had a
seedling stand of only 44%. Seeds soaked in a 40 gram solution of PEG 6000
had significantly greater percent seedling emergence than untreated seeds
after 20, 23, 27 and 30 days of presoaking. Seeds soaked in a 35 gram solution
of PEG 6000 for 20, 23 and 30 days also had significantly greater percent
seedling emergence than the untreated seeds.

A11 seeds pretreated for 27 days required significantly less time for
50% of total seedling emergence (Table 3) than untreated seeds except seeds
soaked in-a 20 and 25 gram solution of PEG 6000. Seeds presoaked for sixteen
days in a 40 gram solution of PEG 6000 were not significantly different than
untreated seeds. However, it took only 23.4 days for 9.1 seedlings (50% of
seedlings emerged) to emerge while the untreated seeds took 25.5 days for
only 5.5 seedlings (50% of seedlings emerged) to emerge. Although the results
were not significantly different between seeds soaked in a 40 gram solution
of PEG 6000 for sixteen days and untreated seeds, it did take less time for
more seedlings from the treated seeds to emerge. Seeds presoaked for sixteen
days in a 40 gram solution of PEG 6000 solution required significantly less

time for 50% of total petri dish germination than untreated seeds (Table 4).

13

14

Percent moisture in seeds soaked in concentrations of 25 grams to
40 grams of PEG 6000/100 ml water showed that the higher the concentration
of PEG the lower the amount of water imbibed by the seeds over a period of
time (Figure 1). Seeds soaked in a 5 gram/100 ml water solution of
PEG 6000 imbibed water faster than seeds soaked in distilled water.
It is possible that PEG 6000 at a low concentration has very limited
hydrogen bonding of water to ether oxygens of PEG 6000. Since the osmotic
pressure in the PEG 6000 solution is less than distilled water, the
seed will imbibe water faster in a 5 gram/100 ml water solution of PEG
6000 because of the greater diffusion pressure deficit. However, as
the concentration of PEG 6000 increases the disruption within the PEG
molecule increases, in turn, increasing the amount of hydrogen bonding
of water to the ether oxygens of PEG 6000 (27). Even though the
diffusion pressure deficit is also increasing, less water is available
to be imbibed by the seed.

The different pretreatment concentrations appeared to have a toxic
effect deve10p (Table 2). Treatments underlined in Table 2 gave the
best total emergence before a steady decline in total emergence
occurred. If seeds presoaked in a 10 gram/100 ml water solution of
PEG 6000 were used as the example, the best total emergence occurred
after six days of pretreatment in PEG 6000 and steadily declined as the
seeds remained in solution longer. It also appeared that as the solution
concentration increased more days of presoaking were required before
the toxic effect was induced. In the case of seeds presoaked for six

days in a 10 gram solution of PEG 6000, the seeds internally probably

15

reached a critical point in their pregermdnation status. If the seeds
were soaked longer than six days, damage to the seed probably resulted
when the seed was air dried. Seeds soaked in a 5 gram/100 ml water
solution of PEG 6000 attained a 70% total emergence after three days
of presoaking. Soaking the seeds in the 5 gram/100 ml water solution
of PEG 6000 longer than three days showed a steady decline in total
emergence whereas seeds soaked in distilled water required eight days
of soaking before they reached maximum total emergence.

Asparagus seeds presoaked in 40 gram/100 ml water solution of
PEG 6000 germinated in the petri dish much sooner than untreated seeds
(Figure 2) and were significantly better than untreated seeds through
the 12th day. For shoot emergence (Figure 3) the asparagus seeds
presoaked in 40 gram/100 ml water solution of PEG 6000 emerged
significantly better than untreated seeds for each day counted except
the 20th day.

Seeds presoaked in distilled water, 5 gram, 10 gram and 15 gram/
100 ml water solution of PEG 6000 germinated while presoaking. This
was why there was missing data for these pretreatments in Tables 2,

3 and 4.

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19

Figure 1. Effect of pretreating asparagus seeds in polyethylene
glycol (PEG) 6000 on percent moisture within the seed
(10 seeds total per replication)

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21

Figure 2. Effect of polyethylene glycol (PEG) 6000 pretreatment
for sixteen days on asparagus seed germination (25
seeds total per replication)

22

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23

Figure 3. Effect of polyethylene glycol (PEG) 6000 pretreatment for
sixteen days on asparagus seedling emergence (25 seeds
total per replication)

24

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RESULTS AND DISCUSSION

Section III

PEG 6000 and CaCl pretreatment of asparagus seeds

2
There was no interaction between seeds soaked in the same solution
and seeds soaked in the changed solution. Seeds treated in a 40 gram/
100 ml water solution of PEG 6000 for sixteen days significantly
improved germination and emergence (Tables 5, 6, 7 and Figure 4)_
compared to untreated seeds. However, when seeds pretreated in PEG

6000 for sixteen days had an additional day of pretreatment in a CaCl2

solution, seedling emergence seventeen days after sowing was enhanced
significantly compared to seeds treated in PEG. However, there were no
significant differences for total germination and total emergence for
seeds presoaked in PEG 6000 for sixteen days compared to seeds soaked
in PEG 6000 for sixteen days followed by one day soaking in CaCl2
(Tables 6 and 7).

Seeds soaked in PEG 6000 for 19 and 22 days and CaCl2 showed a
slight decline in beneficial results when compared to sixteen days of

presoaking (Tables 5 and 6). There was no doubt that soaking in PEG

6000 for sixteen days plus one day in a CaCl2 solution is the best pretreatment.

25

26

Table 5. Effect of polyethylene glycol (PEG) 6000 and calcium
chloride pretreatment of asparagus seeds on the number
seedlings emerged after seventeen days from sowing
(100 seeds total per replication)

Number Emerged

 

 

 

 

 

PEG 6000 CaCl2 Days Soaked

40g/100ml H20 (M) 16 19 22
PEG 1x10‘2 44.0 C* 31.6 c 39.8 c
PEG 5x10"2 36.7 c - 29.1 c 29.7 b
PEG ----- 27.9 b 18.3 b 29.7 b
—-- 1x10'2 3.5 a 3.8 a 11.2 a
-—- 5x10'2 4.0 a 6.2 a 15.8 a

Not Soaked 1.0 a 1.8 a 8.7 a

 

*
Means within columns followed by common letters are not significantly
different at the 5% level (Duncan's Multiple Range Test).

27

Table 6. Effect of polyethylene glycol (PEG) 6000 and calcium
chloride pretreatment of asparagus seeds on total
percent emergence after 45 days from sowing (100
seeds total per replication)

Percent Emerged

 

 

 

 

 

PEG 6000 CaCl2 Days Soaked
40g/lOOml H20 (M) 16 19 22

PEG 1x10"2 79.9 e* 68.7 cd 62.5 b
PEG 5x10"2 72.5 c 72.6 d 53.1 ab
PEG ----- 73.6 c 58.2 be 52.3 ab
--- 1::10’2 43.5 b 52.8 ab 54.7 b
--- 5x10'2 45.7 b 60.0 be 56.3 b

Not Soaked 27.3 a 46.5 a 42.5 a

 

*
Means within columns followed by common letters are not significantly
different at the 5% level (Duncan's Multiple Range Test).

 

 

28

 

 

 

Table 7. Effect of polyethylene glycol (PEG) 6000 and calcium
chloride pretreatment of asparagus seeds on the total
percent germination after 21 days in a petri dish (100
seeds total per replication)
Percent Germinated
PEG 6000 CaCl2 Days Soaked
40g/100md H20 (M) 16 19 22
-2 *
PEG 1x10 84.3 b 79.3 a 83.0 a
PEG 5x10'2 79.7 b 79.2 a 81.6 a
PEG --—-- 80.5 b 70.5 a 75.0 a
--- 1x10"2 66.7 a 75.3 a 73.3 a
--- 5x10‘2 66.3 a 75.2 a 74.2 a
Not Soaked 61.0 a 78.7 a 70.8 a

 

*
Means within columns followed by common letters are not significantly

different at the 5% level (Duncan's Multiple Range Test).

29

Figure 4. Effect of pretreating asparagus seeds in 40g of poly-
ethylene glycol (PEG) 6000 per 100ml of water for six-
teen days and/or one day of soaking in calcium chloride
on the emergence rate (100 seeds total per replication)

30

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SUMMARY AND CONCLUSION

Total seedling emergence was greatly enhanced by presoaking in a

40 gram/100 ml water solution of PEG 6000. Heydecker gg'al. (ll)
theorized that pretreatment in PEG 6000 allows the 'slow' and 'fast'
seeds to reach the same stage of preparedness for germination. With
asparagus seeds it is possible that there is this difference within
the seed population. Some groups of seeds could contain more of a
population of 'slow' seeds than 'fast' seeds causing poor emergence.
Experiments in sections II and III showed a large variability in
percentage of total emergence for untreated seeds. Poor uniformity
for direct seeded asparagus would also cause a problem in the field.

Seeds treated (Tables 5 and 6) with PEG 6000 and CaCl improve chances

2
for a suitable stand of seedlings by allowing the seedlings to emerge
faster in cool soils, reducing the time the seed stays dormant in
the soil.

PEG 6000 has an interesting effect on water uptake of the seed.
Shull (33) found cocklebur seeds had an osmotic potential greater than
900 atmospheres. If water is imbibed by the seed as Meyer and Anderson
(23) postulate, then asparagus seeds soaked in higher concentrations
of PEG 6000 should absorb more water than seeds soaked in distilled water.
However, this is not the case with PEG 6000. As the concentration

increases, PEG 6000 increases its affinity for water (27). If a

concentration of PEG 6000 is selected as the 40 gram/100 ml water solution

31

32

which was used on asparagus seeds, then less water is imbibed by the
seed compared to imbibition in distilled water (Figure 1). This
decrease in water imbibition allows the seed to advance its pregermination
metabolism part way to germination but because of the reduced water
uptake the seed will not germinate in the solution.

Apparently the seed does not have to completely germinate for it
to be damaged by either presoaking or drying (Table 2). In this case
drying the seed is the damaging effect. The underlined numbers show
the best total emergence in the particular solutions. After this soaking
time the total percent emergence drops off steadily. It is possible that
presoaking the seed longer advances the seed beyond a desirable stage
of pregermination and air drying the seed for 24 hours damages it.
High concentration of PEG 6000 solution increases the soaking duration
necessary to induce seed damage by air drying.

With asparagus seeds it is possible that Ca+2 is bound by pectins
in the middle lamella (6). It also could trigger the metabolism of
carbohydrates such as cellulose, callose and pectin as it does in pollen
germination, in turn possibly benefiting asparagus seed germination.

The results obtained by working with PEG 6000 are very exciting.
By pretreating asparagus seed for sixteen days in a 40 gram/100 ml water
solution of PEG 6000 and one day in a lxlO-ZM solution of CaCl2 more
direct seeding of asparagus beds could be used at a savings to the grower
who now plants crowns. This is just the beginning of the experiments

that could be performed using PEG 6000. One area could be pretreating

33

seeds with a PEG 6000 solution and a nutrient mixture instead of water.
Another area would be PEG 6000 treating of asparagus seeds with a
higher concentration of the chemical, and finally PEG 6000 treating

of seeds followed by soaking in different chemical solutions. This

work shows much promise and should definitely be continued.

LIST OF REFERENCES

10.

11.

12.

LIST OF REFERENCES

Anonymous. 1973. Progress report of asparagus research.
Research Report 217. Michigan State Univ. Agric.
Expr. Station.

Anonymous. 1974. Report of asparagus research. Agric. Engr.
Dept. Michigan State University.

Abeles, F. B. and J. Lonski. 1969. Stimulation of lettuce seed
germination by ethylene. Plant Physiol. 44:277-280.

Austin, R. B., P. C. Longden, and J. Hutchinson. 1969. Some
effects of 'hardening' carrot seeds. Ann. Bot. 33:883-895.

Bleak, A. T. and W. Keller. 1972. Germination and emergence of
selected forage species following preplanting seed treat-
ments. Crop Sci. 21:9-13.

Brewbaker, J. L. and B. H. Kwack. 1963. The essential role of
calcium ions in pollen germination and pollen tube growth.

Borthwick, H. A. 1925. Factors influencing the rate of germina-
tion of the seed of Asparagus officinalis. Calif. Tech. Paper
18.

 

Bradbeer, J. W. and N. F. Pinfield. 1967. Studies in seed dorm-
ancy. III. The effects of gibberellin on dormant seeds of
Corylus avellana L. New Phytol. 66:515-523.

 

Hegarty, T. W. 1970. The possibility of increasing field estab-
lishment by seed hardening. Hort. Res. 10:59-64.

Hendricks, S. B. and R. B. Taylorson. 1974. Promotion of seed
germination by nitraten nitrite, hydroxylamine, and ammonium
salts. Plant Physiol. 54:304-309.

Heydecker, W., J. Higgins, and R. Gulliver. 1973. Bringing seeds
to the brink of germination. The Grower. 81:1134-1135.

Janes, B. E. 1966. Adjustment mechanisms of plants subjected to

varied osmotic pressures of nutrient solution. Soil Science.
101:180-188.

35

13.

14.

15.

l6.

17.

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240

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36

Janes, B. E. 1974. The effect of molecular size, concentration
in nutrient solution, and exposure time on the amount and
distribution of polyethylene glycol in pepper plants. Plant
Physiol. 54:226-230.

Kaufmann, M. R. 1969. Effects of water potential on germination
of lettuce, sunflower, and citrus seeds. Can. J. Bot.
47:1761—1764.

Kaul, R. 1966. Relative growth rates of spring wheat, oats,
and barley under polyethylene glycol-induced water stress.
Can. J. Plant Science. 47:611-617.

Ketring, D. L. and P.W. morgan. 1971. Physiology of oil seeds.
11. Dormancy release in virginia-type peanut seeds by
growth regulators. Plant Physiol. 47:488-492.

Komoti, S. 1958. studies on temperature treatments of seeds.
II. Dormancy and germinating temperature in garden aspar-
agus seeds. Hakkaido Nogyo Shikenjo Res. Bul. of the Nat.
Agric. Expr. Station. 73:9-19.

Knudson, L. L. and T. W. Tibbitts. 1973. Wickeaction method
for germination of seeds. Hort. Sci. 8:472.

Kwack, B. H. 1964. The effect of calcium on pollen germination.
Proc. Amer. Soc. Hort. Sci. 86:818-823.

Lagerwerff, G. V., G. Ogata, and H. E. Eagle. 1961. Control
of osmotic pressure of culture solutions with polyethylene
glycol. Science. 133:1486-1487.

Lawlor, D. W. 1970. Absorption of polyethylene glycols by
plants and their effect on plant growth. New Phytol.
69:501-513.

Manohar, M. S. 1966. Effect of "osmotic" systems on germina-
tion of peas (Pisum sativum L.). Planta. 71:81-86.

 

Meyer B. S. and D. B. Anderson. 1952. Plant Physiology. D. Van
Nostrand Company, Inc. New York.

Mexal, J., J. T. Fisher, J. Osteryoung, and C. P. P. Reid. 1975.
Oxygen availability in polyethylene glycol solutions and its
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37

Michel, B. E. 1970. Carbowax 6000 compared with mannitol as a
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Oyer, E.B. and D. E. Koehler. 1966. A method of treating
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p. 626.

Putnam, A. R. 1972. Efficany of a zero-tillage cultural system
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Roberts, E. H. and D. L. Roberts. 1972. Moisture content of
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Robbins, W. W. and H. A. Borthwick. 1925. Development of the
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Sanok, W. J. 1972. The influence of carbon dioxide and ethy-
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State University.

Shull, C. A. 1916. Measurement of the surface forces in soils.
Bot. Gaz. 62:1-31.

Takatori, F. H., J. I. Stillman, and B. Power. 1968. Direct
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Takayanagi, K. and J. F. Harrington. 1971. Enhancement of germ-
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47:521-524.

Tarkow, H., W. C. Feist, and C. F. Southerland. 1966. Interac-
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Toole, V. K., W. K. Bailey, and E. H. Toole. 1964. Factors
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39:822-832.

Wilcox, G. E. and P. E. Johnson. 1970. Direct seeding tomatoes
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Purdue Univ. Agric. Expr. Station.

APPENDIX

39

Table 8. Effect of cold treatment of asparagus seeds on sub-
sequent seedling development after 36 days in a petri
dish (50 seeds total per replication)

 

Cold Average Shoot Number of
Treatment (8°F) Fresh Weight Length Seeds Germinated

(hours) (grams) (mm)

0 0.110 5.1 22.8

1 0.134 5.2 25.6

2 0.089 4.8 26.8

3 0.224 5.1 23.0

4 0.057 3.7 19.2

 

There are no significant differences

40

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41

Table 10. Effect of Ethephon pretreatment of asparagus seeds on
subsequent seedling development after 40 days in a
petri dish (50 seed total per replication)

 

Average Shoot Number of
Ethephon Fresh Weight Length Seeds Germinated
(PPm) (gm) (mm)
1000 0.016 2.6 15.2
750 0.010 2.1 13.4
500 0.036 1.0 14.8
250 0.110 5.1 13.4

Not Soaked 0.110 5.1 22.8

 

42

Table 11. Effect of concentrated H 80 scarification of asparagus
seeds on germination (33 seeds per replication)

Percent Germination

 

Time in H SO Days in Petri Dishes

 

 

 

2 4
(min) 11 28
5 0.1 0.3
10 0.0 0.0
15 0.0 0.3

Not Soaked 12.7 20.0

 

MIC CIH IGAN STATE UNIVERSITY LIBRARIE