Note: Descriptions are shown in the official language in which they were submitted.
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COLD-PLASMA DEPOSITION TREATMENT OF SEEDS AND
OTHER LIVING MATTER
FIELD OF THE INVENTION
This invention pertains generally to the field of plasma processing of
materials and particularly to plasma coating of seeds and other living matter.
BACKGROUND OF THE INVENTION
The treatment of seeds can provide benefits to the planted seed in a
more economical and less polluting manner than the alternative of field
application.
There are two major objectives for the treatment of seeds: to alleviate stress
associated with the soil environment and to directly increase growth. Stress
associated with the soil environment may be biotic or abiotic in nature. For
example, the most common seed treatments alleviate biotic stress by reducing
the
damage caused by seed or soil borne pests (e.g., insects, fungi, etc.) on
seeds and
seedlings. Abiotic stress alleviation has been obtained by, for example,
modifying
the soil water oxygen relations surrounding the germinating seeds. Improvement
or
modification of plant growth and development can occur by direct application
of
nutrients or plant growth regulators to seeds.
One method that has been used to apply materials to seeds is seed
coating, the direct application of material to a seed. Typically, seed coating
refers
to the application of useful materials) to a seed without changing its general
shape
or size, whereas pelleted seed refers to seed to which inert fillers have been
added
to increase the apparent size and weight of the seed. Pelleted seed may be
produced
by a dry powder process, which can have the disadvantages that the powders may
not adhere well, they may result in poor loading (causing planting problems),
the
powder may be applied non-uniformly, and significant amounts of dust may be
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generated (which can be hazardous to operators). In film coating of seeds, the
active materials are dispersed or dissolved in a liquid adhesive which is
applied to
the seeds either with a fluidized bed treatment or using a pharmaceutical
coating
drum. Such film coatings can be applied in multiple layers and can increase
the
seed weight typically from 1 % to 10 % . Generally, such coatings are less
than 0.1
mm in thickness.
Seeds produced by commercial seed companies are commonly treated
with insecticides and fungicides to enhance the survivability and germination
rate of
the planted seed. A significant concern that has arisen as a result of such
treatment
of seed is the potential health hazards posed to farmers and other individuals
who
are involved in the transport and storage of such seed because of the
potential
airborne release of particles and toxins from the surfaces of the treated
seed. One
approach to this problem adopted by many seed companies has been the coating
of
the fungicide and insecticide treated seed with a polymer film to encapsulate
the
seeds and thereby significantly reduce the release of toxic materials into the
atmosphere during storage and handling of the seeds. The polymer coating of
the
seeds can also improve the survivability of seedlings under cold and wet
conditions.
Conventional seed treatment systems generally apply a coating to the
seeds by mixing the seeds with a slurry of chemicals and water or by applying
a
water based mist to the seeds. For coating of seeds with polymer films in
particular, mixing the seeds with a liquid slurry or agitating the seeds in a
mist of
the film forming material may result in uneven thicknesses of coatings of the
seeds.
A particular problem encountered with water based slurries and mists is that
some
amount of water is taken up by the seeds during the treatment process. If the
water
absorbed by the seed is excessive, under some conditions the treated seed will
be
subject to premature germination and reduced storage life.
A particular effort has been directed to the control of the timing of
germination in seeds. Under certain conditions, delayed germination of seeds
would greatly enhance the storage life of the seeds, whereas for other
applications,
enhanced or accelerated germination would provide better growth opportunities
.
The coating processes that have conventionally been used for seeds are not
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necessarily well suited to tailor the germination characteristics of the seeds
after
treatment.
SUMMARY OF THE INVENTION
In accordance with the present invention, living matter and
particularly seeds are treated by exposing the living matter to a cold plasma
to form
a plasma reacted deposit on the surfaces of the living matter. Polymer films
and
other coatings having desired characteristics and closely controlled
thicknesses can
be applied to seeds and other appropriate living matter in accordance with the
invention to encapsulate seeds treated with insecticides and fungicides, to
control
the germination characteristics of the seeds, either to accelerate or delay
germination, to protect the seeds from damage, to adhere chemicals or
biological
materials to the surfaces of the seeds or other appropriate living materials
such as
fungal mass, pollen, spores, and bacteria, to enhance the flow characteristics
of
bulk seeds, or to carry out a combination of such treatments. It is found
that, in
accordance with the invention, the plasma treatment conditions do not
significantly
affect the viability of the live seeds and other appropriate living matter
after
treatment. In addition, plasma treatment in accordance with the invention can
be
carried out to maintain the moisture level within the seeds or even to remove
moisture during the plasma treatment process. Because the plasma treatment
process in accordance with the invention is carried out under dry conditions,
no
additional moisture need be added to the seeds during the process.
In a preferred method of treating living seeds in accordance with the
invention to enhance the surface properties of the seeds, the seeds to be
treated are
enclosed in a reaction chamber, the reaction chamber is evacuated to a base
level,
and a selected gas is supplied to and a selected gas pressure is established
in the
reaction chamber. The gas is provided from a gas source from which the deposit
may be formed by a plasma reaction. A cold plasma is ignited in the gas in the
chamber and the seeds are exposed to the plasma for a selected period of time
to
react to form a plasma reacted deposit on the surfaces of the seeds. The gas
in the
chamber may be ignited by coupling RF power to the gas in the chamber in
various
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ways, including capacitive coupling and inductive coupling. In addition, the
RF
power may be coupled in pulses to the plasma in the reaction chamber.
Virtually any type of seed can be treated in accordance with the
present invention. For example only, these include standard food seeds such as
those for beans, corn, radishes, peas, soybeans, etc.
The gas provided by the gas source that is supplied to the reaction
chamber may be any of the various gases which will provide a plasma reacted
deposit on the surface of the seeds. By way of example only, such gases can
include organic gases such as octadecafluorodecalin (ODFD), aniline,
cyclohexane,
and hydrazine. The deposit of plasma reacted film from materials such as ODFD
provides tetrafluoroethylene macromolecular layers which yield smooth and non-
sticky surfaces. Such film coatings may be utilized to delay germination of
seeds
and reduce the uptake of water by seeds, in part because of the hydrophobicity
of
the deposited film. Other materials that may be deposited from a gas within
the
reaction chamber include macronutrients such as nitrogen, phosphorous,
potassium,
and sulfur, which may be deposited on and attached to the seed surface using
an
appropriate organic based plasma containing the nutrients. Micronutrients,
such as
boron, zinc, and chlorine may be attached in the same way. Growth promoters,
e.g., gibberllic acid type structures, may be attached to seeds in a similar
way.
Because the plasma treatment is carried out typically under lower
than atmospheric pressures and with a dry gas, no additional water need be
absorbed by the seeds during the treatment process. In this manner, unintended
early germination or potential rot of the seeds, which might result from water
based
treatment of the seeds, is avoided.
The plasma treatment process of the invention allows extremely thin
and precisely controlled coatings to be obtained. In addition, because the
surfaces
to be coated and the coating layer precursors are activated under plasma
environments, excellent adhesion of the deposited material is obtained.
Further objects, features, and advantages of the invention will be
apparent from the following detailed description when taken in conjunction
with the
accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
Fig. 1 is a schematic view of a plasma reactor system for carrying
out the present invention.
Fig. 2 is a survey X-ray photo-electron spectroscopy for chemical
analysis (ESCA) graph for seed (beans) treated in accordance with the present
invention.
Fig. 3 is a high resolution X-ray photo-electron spectroscopy for
chemical analysis (ESCA) graph for seed (beans) treated in accordance with the
present invention.
Fig. 4 are bar graphs illustrating percent germination of Pisum
sativum variant Little Marvel over time for a control sample and for a sample
treated with CFa RF plasma.
Fig. 5 are bar graphs illustrating percent germination over time of
Pisum sativum variant Alaska for a control sample and for a sample treated
with a
CF4 RF plasma.
Fig. 6 are bar graphs illustrating percent germination over time for
Raphanus sativus for a control sample and for a sample treated with a CFa RF
plasma.
Fig. 7 are bar graphs illustrating percent germination over time for
Glycine max for a control sample and for a sample treated with a plasma
containing
aniline .
Fig. 8 are bar graphs illustrating percent germination over time for
Zea mays for a control sample and for a sample treated with a plasma
containing
aniline.
Fig. 9 are bar graphs illustrating percent germination over time for
Zea mays for a control sample and for samples treated at two different
pressures
with a plasma containing cyclopentane.
Fig. 10 are bar graphs illustrating percent germination over time for
Glycine max for a control sample and for samples treated with a plasma
containing
cyclopentane at two different pressures.
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Fig. 11 are bar graphs illustrating percent germination over time for
Glycine max for a control sample and for a sample treated with a plasma
containing
perfluorodecaline.
Fig. 12 are bar graphs illustrating percent germination over time for
Zea mays treated with plasma containing perfluorodecaline.
Fig. 13 are bar graphs illustrating percent germination over time for
Zea mays for a control sample and for samples treated with a plasma containing
hydrazine and a plasma containing perfluorodecaline.
Fig. 14 are bar graphs illustrating percent germination over time for
Zea mays for a control sample and for samples treated with perfluorodecaline
for
various treatment times.
Fig. 15 are bar graphs illustrating percent germination over time for
Phaseolus vulgaris for a control sample and for samples treated with a plasma
containing perfluorodecaline for various treatment times.
DETAILED DESCRIPTION OF THE INVENTION
The present invention encompasses cold plasma reacted deposit of
material on the surfaces of living matter such as seeds without significantly
affecting
the viability of the living matter. Cold plasmas are non-thermal and non-
equilibrium plasmas, versus hot plasmas which are thermal or equilibrium
plasmas.
In a cold plasma, the kinetic energy of the electrons is high while the
kinetic energy
of the atomic and molecular species are low; in a hot plasma, the kinetic
energy of
all species is high, and organic materials would be damaged or destroyed in a
hot
plasma. In a cold plasma the plasma temperatures are near normal atmospheric
temperatures and generally well below the boiling point of water. It has been
discovered in accordance with the present invention that appropriate cold
plasma
treatments of living matter such as seeds not only does not destroy the seeds
but
also allows the seeds to remain viable so that they will germinate when
planted
under appropriate conditions.
With reference to Fig. l, an exemplary cold plasma reactor system
which may be utilized to carry out the invention is shown generally at 10. The
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reactor system includes a cylindrical reaction vessel 11 (e.g., formed of
Pyrex
glass, lm long and 10 cm inside diameter) which is closed at its two ends by
disk
shaped stainless steel sealing assemblies 12 and 13. The end assemblies 12 and
13
are mounted to mechanical support bearings 16 and 17 which engage the sealing
assemblies 12 and 13 to enable rotation of the reaction vessel 11 about its
central
axis, i.e., the central axis of the cylindrical reaction vessel. Hollow shaft
(e.g. ,
0.5" inside diameter) ferrofluidic feedthroughs 19 and 20 extend through the
sealing
assemblies 12 and 13, respectively, to enable introduction of gas into and
exit of gas
from the reaction chamber. A semicylindrical, outside located, copper upper
electrode 21 is connected to an RF power supply 22, and a lower, similar
semicylindrical copper electrode 24 is connected to ground (illustrated at
25). The
two electrodes 21 and 24 closely conform to the cylindrical exterior of the
reaction
vessel 11 and are spaced slightly therefrom, and together extend over most of
the
outer periphery of the reaction vessel but are spaced from each other at their
edges
a sufficient distance to prevent arcing or discharge between the two
electrodes. The
foregoing arrangement is only exemplary of the many electrode arrangements
that
may be used to couple power to the plasma. For example, a central internal
electrode (not shown) may be extended into the reaction chamber along the
central
axis rather than using external electrodes.
The present invention carries out a plasma reacted deposit of material
on seeds and other living matter such as with a film formed from a gas which
is
capable of depositing a cold plasma mediated film. The source gas is held in
containers 26, e.g., storage tanks. The source gases in the containers 26 may
be a
variety of gases (e.g., argon, ammonia, air, oxygen, octadecafluorodecalin,
etc.)
typically compressed under pressure. The source gas may also be provided from
liquid or solid source materials that are volatilized, such as by heating, or
from
liquid or solid particulate aerosols (e.g., nitrogen fixing bacteria), all of
which shall
be referred to herein as a "gas." The flow of gas from a source cylinder 26 is
controlled by needle valves and pressure regulators 27 which may be manually
or
automatically operated. The gas that passes through the control valves 27 is
conveyed along supply lines 28 through flow rate controllers 30 to a gas
mixing
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chamber 31 (e.g., preferably of stainless steel), and an MKS pressure gauge 32
(e.g., Baratron) is connected to the mixing chamber 31 to monitor the pressure
thereof. A supplementary valve 33 is connected to the mixing chamber 31 to
allow
selective venting of the chamber as necessary. The mixing chamber 31 is
connected
to the feedthrough 19 that leads into the interior of the reaction chamber 11.
A
digital controller 34 controls a driver motor 35 that is connected to the
assembly 19
to provide controlled driving of the reaction chamber in rotation _
The second feedthrough 20 is connected to an exhaust chamber 37 to
which are connected selectively openable exhaust valves 38, 39 and 40, which
may
be connected to conduits for exhaust to the atmosphere or to appropriate
recovery
systems or other disposal routes of the exhaust gases. A liquid nitrogen trap
42 is
connected to an exhaust line 43 which extends from the chamber 37 by stainless
steel tubing 44. The trap 42 may be formed, e.g., of stainless steel (25 mm
inside
diameter). A mechanical pump 45 is connected through a large cross-section
valve
46 via a tube 47 to the trap 42 to selectively provide vacuum draw on the
reactor
system to evacuate the interior of the reaction chamber 11 to a selected
level.
The power supply 12 is preferably an RF power supply (e.g., 13.56
MHz, 1,000 W) which, when activated, provides RF power between the electrodes
21 and 24 to capacitively couple RF power to the gas in the reaction chamber
within
the reaction vessel 11. Conventional coils for inductively coupling RF power
to the
plasma may also be used (e.g., a coil extending around the reaction vessel
11). A
Farraday cage 50 is preferably mounted around the exterior of the reaction
vessel to
provide RF shielding and to prevent accidental physical contact with the
electrodes.
The reactor vessel may be rotated by the drive motor 35 at various
selected rotational speeds (e.g., 30-200 rpm), and it is preferred that the
vacuum
pump and associated connections allow the pressure in the reaction chamber
within
the vessel to be selectively reduced down to 30 mT.
The following are examples of commercial parts that may be
incorporated in the system 10: RF-power supply 22 (Plasma Therm Inc. RTE 73 ,
Kresson N.J. 08053; AMNS-3000 E; AMNPS-1); mechanical vacuum pump 45
(Leibold-Heraeus/Vacuum Prod. Inc., Model: D30AC, Spectra Vac Inc); pressure
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gauge 32 (MKS Baratron, Model: 622AO1TAE); digitally controlled rotating
system 34, 35 (DC motor Model 42528, Dayton Electric Mfg. Co.; DART
Controls Inc. controller).
In utilization of the plasma treatment system 10 in accordance with
the invention, it is generally preferred to carry out a plasma-enhanced
cleaning of
the reactor prior to treatment to eliminate possible contaminants. An
exemplary
cleaning step includes introduction of oxygen gas from one of the tanks 26
into the
reaction chamber and ignition of a plasma in the gas at, e.g., a power level
of 300
W, a gas pressure of 250 mT, an oxygen flow rate of 6 scan, and a typical
cleaning
period of 15 minutes.
For carrying out treatment of seeds and other living material in
accordance with the invention, the reactor is opened to allow access to the
interior
of the reaction vessel 11 by, e.g., disconnecting one of the vacuum sealing
assemblies 19 or 20 from the cylindrical reaction vessel, and inserting the
seeds into
the interior of the vessel, followed by resealing of the assemblies into
vacuum tight
engagement with the reaction vessel 11. Sealable ports may also be formed in
the
sealing assemblies. The pump 45 is then operated to evacuate the plasma
reactor to
a desired base pressure level based on the seed origin water vapor or the
artificially
supplied plasma gases and vapors. The desired gas which will be used to form a
reaction product film on the seeds is then introduced from the source
containers 26,
and a desired gas pressure level in the reaction chamber is established. The
RF
power supply 22 is then turned on (generally, it is preferred that the power
be
supplied in pulses) to ignite the plasma in the gas introduced into the
reaction
chamber defined by the reaction vessel 11 and the end sealing assemblies 12
and 13.
For treating seeds, it is preferred that the drive motor 35 be operated to
rotate the
reaction chamber 11 to tumble the seeds during the plasma reaction process so
that
all surfaces of the seeds are exposed to the plasma for a relatively uniform
period of
time to enable the surfaces of the seeds to have a uniform deposit of material
thereon. The material deposited may be very thin, e.g., comprising a monolayer
of
molecules (~ 20 t~ thick), which is strongly bonded to the surface and which
functionalizes the surface for various purposes. It is a particular advantage
of the
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present invention that because the seeds are exposed to a dry gas during the
plasma
process rather than a liquid based slurry or a mist, the thickness of the
coating on
the seeds can be well controlled and unintended build-up of material on some
surfaces of the seeds or inadequate coverage of other seed surfaces, which can
occur with liquid based treatments, is avoided. In addition, as noted above,
because
the seeds are exposed to a dry gas during plasma treatment, no additional
moisture
need be introduced into the seeds, and because of the evacuation of the
chamber
below atmospheric pressure, some removal of moisture from the seeds during
plasma processing can be obtained if desired. After the selected period of
time,
sufficient to provide a desired film deposited from the source gas onto the
surface of
the seeds, has elapsed, the power supply 22 is turned off, the pump 45 is then
operated to evacuate the reaction chamber to draw out the remaining source
gases
and any byproducts which can be vented to the atmosphere or disposed of as
appropriate, and then atmospheric air is introduced into the chamber to bring
the
pressure in the reaction chamber to normal atmospheric pressure before one of
the
sealing assemblies 12 or 13 is opened to allow removal of the treated seeds.
If desired, the plasma treatment processes can be stopped periodically
to allow the collection of samples of the seeds for analytical and biological
evaluations .
In addition to the preferred RF plasma reaction apparatus discussed
above, the invention may be carried out using other plasma treatment
apparatus,
including static inductively or capacitively coupled RF plasma reactors, DC-
discharge reactors, and atmospheric pressure barrier discharges. Such
apparatus
are not preferred for certain applications of the invention. Static reactors
may yield
non-uniform treatment of the seeds or other material. Atmospheric pressure
discharges usually require a narrow electrode gap, and they generally cannot
uniformly expose the seed (or other particulate matter) surfaces to the
discharge.
Additionally, because of the particulate nature of seeds etc., the ability to
use
vacuum tight seals is limited, which may result in contamination problems.
Barrier
discharge processes are also less efficient because of the short free path of
the
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plasma particles and, consequently, the fast recombination of the active
species in
the gas phase.
The utilization of the present invention to provide cold-plasma
mediated deposit of materials including films on seeds and other living matter
can
introduce significant surface modifications to the seeds without affecting the
viability of the seeds. The surface deposit may be hydrophobic, delaying
germination of seeds, or hydrophilic, accelerating germination. Plasma
treatment in
accordance with the invention can allow the deposit of bioactive molecules,
fungicides (e.g., organal-copper derivatives), and even bacteria (e.g.,
nitrogen-
fixing bacteria) onto seed surfaces. Where the seeds have previously been
treated
with fungicides and insecticides, the surface coating provided by the present
invention using appropriate source gases can form films that seal in the
insecticide
and fungicide to minimize the amount of toxic dust that may be generated
during
storage and handling of the seeds.
A variety of source gases may be utilized to provide a gas that will
deposit a coating on the surfaces of the seeds by the cold plasma process. For
purposes of exemplifying the invention only, such source gas can include
octadecafluorodecalin (ODFD), aniline, cyclohexane, hydrazine,
hexafluoropropane
oxide, perfluorocyclohexane, hexamethyldisoloxane, cyclosiloxanes, vinyl
acetate,
polyeyhylene gylcol oligomers, mixtures of these, as well as many others.
The active species of the plasma, including charged and neutrals
species, have energies comparable with the chemical bonds of organic
compounds,
and consequently these species can cleave molecules and accordingly can
generate
active molecular fragments, such as: atoms, free radicals, ions of either
polarity,
etc. These molecular fragments, assisted by electrons and photons, generate
specific gas phase and surface recombination reaction mechanisms which can
lead
to the formation of new molecular or macromolecular structures, and to the
extraction of low molecular weight, volatile molecular fragments of substrate
origin.
By controlling the external (power, pressure, flow rate, etc.) and
internal (energy distribution of charged and neutral species, particle
densities, etc.)
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plasma parameters, these processes can be tailored to provide predominant
recombination processes to deposit material from the plasma onto the seeds or
other
material being treated.
Other factors like molecular structures, gas composition and pulsing
characteristics also can influence significantly the nature of the plasma-
mediated
reaction mechanisms. Carbon tetrafluoride plasmas do not deposit fluorinated
macromolecular layers under common RF cold plasma conditions due to the
intense
etching effects related to the high plasma-generated fluorine atomic
concentrations.
However, the presence in the gas mixture of fluorine atom scavengers (e.g.
hydrogen) allows the deposition of macromolecular layers. Thus, under
appropriate
conditions, source gases such as CFa can be utilized to deposit material on
surfaces
rather than etch the surfaces.
The reaction mechanisms related to deposition and etching processes
are significantly different. Etching reactions are characterized by the fast
generation of low molecular weight, volatile molecules and molecular
fragments,
while deposition reactions require less volatile, higher molecular weight
species.
Many types of seeds or other living matter may be treated in
accordance with the present invention. Again, for exemplification only, such
living
matter which may be treated in accordance with the invention includes beans
such
as Phaseolus vulgaris, corn (Zea mays), radish (Raphanus sativus), peas (Pisum
sativum), and soybeans (Glycine max).
Typical radio frequency (RF) power applied to the plasma is in the
range of 150 W, with typically a pulsed application of the RF power, e.g.,
SOO~s
pulse period and 30 % duty cycle. A typical pressure in the reactor during the
discharge is about 200 mT with plasma flow rates of 6 scan. These are typical
only and are not to be construed as limiting or defining the scope of the
process
conditions that may be used. Various treatment times may be carried out to
provide
the desired thickness of coating, depending on the source gas, while retaining
the
viability of the seeds. Typical treatment times may range from a half a minute
to
20 minutes although longer or shorter times may be appropriate.
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Survey and high resolution X-ray photo-electron spectroscopy for
chemical analysis (ESCA) can be carried out to determine the surface
characteristics
of the treated seeds. For example, with seeds (beans) treated with ODFD, ESCA
data indicate the presence of a relatively high relative fluorine atomic
concentration
on the seeds' surfaces and the existence of dominant CFX non-equivalent Cls
carbon
functionalities, as illustrated in Figs. 2 and 3. These data indicate that the
ODFD-
plasma exposed seeds were coated with polytetrafluoroethylene (Teflon-like)
macromolecular layers. Comparative atomic force microscopy images taken of the
seeds show that the seeds have a smooth surface in comparison to untreated
seeds.
The following examples illustrates the viability and the germination
rates of the seeds treated in accordance with the invention. After plasma
treatments, seeds were placed in seed germination trays. Control samples
consisted
of seeds that had been kept under vacuum condition only. Using sterile
techniques
and a laminar flow hood, treated and untreated seeds were transferred from
polyethylene bags into the germination trays. Each tray was provided with
moist
seed germination paper that was folded over to completely cover the seeds.
Germination paper was maintained in a moist condition by misting with
distilled
water as required. The humidity within each tray was maintained at a level
over
90% relative humidity. The germination trays were then introduced into a
germination growth chamber (from Hoffman Manufacturing Inc.) under the
following selected environmental conditions: day/night temperature:
28°C/25°C;
photo exposure: 16 hours; average photosynthetic photon flux (PPF) equal to
100p mol/mZs at the seeds' surface. The seeds were examined every 24 hours
under the laminer flow hood for signs of germination. When radical germination
was noted, seeds were counted as having germinated and the time was recorded.
Seeds were continuously counted until the germination rate was consistent over
a
three-day period.
The germination data indicated that CFa treatment of radish and pea
seeds exhibited delayed germination; aniline-plasma treated soybeans and corn
seeds
recorded accelerated germination; cyclopentane and hydrazine plasma treatment
shortened only slightly the germination of soybeans and did not affect the
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germination of corn (experiments performed at two different pressures, 70 and
150
mT did not generate significant differences in the germinations); and
perfluorodecaline-plasmas substantially delayed the germination growth of bean
and
corn seeds, with the longer the plasma treatment time, the longer the delay of
germination. Fig. 4 illustrates results with Little Marvel variant of Pisum
sativum
treated with carbon tetrafluoride RF plasma at 200 mT for five minutes to
provide a
plasma mediated deposit on the surfaces of the seeds. Fig. 5 shows a similar
plasma treatment for the Alaska variant. In both cases, germination is
delayed.
Fig. 6 shows the results for a similar CFa plasma treatment of Raphanus
sativus
illustrating delayed germination for the plasma treated seed, but there was
essentially no difference in long term germination versus the control. Fig. 7
shows
the results for plasma treatment of Glycine max with aniline containing
plasma,
illustrating the acceleration of germination for the plasma treated seed with
no
difference in long-term germination over the control. Similar results were
obtained
for a similar plasma treatment with an aniline containing plasma for Zea mays
as
shown in Fig. 8. Fig. 9 illustrates the results for Zea mays germination for
cyclopentane plasma treatment at two different pressures, illustrating an
accelerated
germination for the seeds treated at the higher pressure but with no long-term
difference in germination compared to the control. Fig. 10 shows the results
for a
similar treatment of Gylcine max with cyclopentane, illustrating accelerated
germination for the plasma treated seeds with minor differences in long-term
germination of the plasma treated seed as compared with the control. Fig. 11
shows the results for treatment of Glycine max with perfluorodecaline
containing
plasma, illustrating delayed germination for the plasma treated seed. Fig. 12
shows
the results for a similar plasma treatment of Zea mays with perfluorodecaline,
illustrating significantly delayed germination and reduced long-term
germination for
the plasma treated seed under plasma treatment conditions of 300 mT pressure
for
ten minutes. Fig. 13 shows comparative results for Zea mays treated with
plasmas
containing hydrazine and plasmas containing perfluorodecaline at 200 mT for 20
minutes. The comparative data show no significant long-term difference in
germination between the plasma treated seed and the control, but with a
significant
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delay in germination for the perfluorodecaline plasma treated seed and a
slight
acceleration of germination for the hydrazine treated seed. Fig. 14
illustrates the
results for several samples of Zea mays treated with plasma containing
perfluorodecaline at 200 mT for plasma treatments times of 2, 5 and 20 minutes
.
As illustrated therein, all plasma treatments significantly delayed early
germination
of the treated seed while long-term germination was slightly reduced for the
two
minute treated seed and significantly reduced for the 20 minute treated seed.
Fig .
shows the results for similar plasma treatments of Phaseolous vulgaris for
treatment with plasmas containing perfluorodecaline at 200 mT for treatment
times
10 of 2, 5 and 20 minutes. The data show that germination was delayed for all
of the
treated samples, with the amount of the delay in germination directly related
to the
length of the treatment time. However, the long-term germination rates for all
treatment times were essentially the same, slightly reduced from the control
germination rate. The foregoing data illustrate that germination rates can be
15 accelerated or delayed for various of types of seed by plasma treatments
with
appropriate plasma source gases, with long-term germination rates that are
similar
or essentially identical to untreated seeds by appropriate choice of plasma
treatment
conditions such as gas pressure and treatment time.
From these data, several conclusions can be drawn. Cold-plasma
treatments in accordance with the invention can induce significant surface
modifications on various seeds, while maintaining the viability of the seeds.
Plasma
deposited thin fluorocarbon layers can cause delays in seed germination, which
may
be due to the hydrophobic nature of such films and, consequently, to the
reduced
water permeation through the films to the seeds. Such delayed germination
seeds
may be intermixed with regular germination seeds to provide phased germination
of
seeds being planted, and seeds treated in this manner may be stored for longer
periods of time, e. g. , for more than one year or to be conserved during
space
travel, etc. The plasma deposition process allows immobilization of bioactive
molecules, such as fungicides and bacteria (e.g., nitrogen-fixing bacteria) or
plant
nutrients on the seed surfaces. While the plasma treatment may be carried out
in
accordance with the invention to deposit protective films over previous
treatments
CA 02368180 2001-10-09
WO 00/78124 PCT/US00/17214
-16-
including bacteria, the seeds may be pretreated by a plasma cleaning process
to
clean the surfaces of the seeds and to sterilize the seed surfaces to kill
bacteria and
fungus, etc., before applying a protective film coating in accordance with the
invention.
It is understood that the invention is not confined to the particular
embodiments set forth herein as illustrative, but embraces such modified forms
thereof as come within the scope of the following claims.
