Note: Descriptions are shown in the official language in which they were submitted.
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METHODS FOR IMPROVING GROWTH AND CROP PRODUCTIVITY OF PLANTS
BY ADJUSTING PLANT HORMONE LEVELS, RATIOS AND/OR CO-FACTORS
BACKGROUND OF THE INVENTION
1. Field of the Invention
[001] The present invention generally relates to methods for improving the
growth and crop productivity of plants by adjusting plant hormone levels
and/or
ratios. These methods are also useful for improving the resistance of plants
to
infestation by insects and pathogens, while, at the same time, improving plant
growth
by controlling plant hormones. More specifically, the present invention is
directed to
methods for achieving those goals by applying an effective amount of one or
more
plant hormones to the plant tissue. Alternatively, these goals are achieved by
applying to the plant tissue other substances that effect the level of one or
more
plant hormones in the plant tissue, causing the hormone(s) to move into a
desired
range.
1. Description of the Background
[002] Plant hormones have been known and studied for years. Plant
hormones may be assigned to one of five categories: auxins, cytokinins,
gibberellins, abscisic acid and ethylene. Ethylene has long been associated
with
fruit ripening and leaf abscission. Abscisic acid causes the formation of
winter buds,
triggers seed dormancy, controls the opening and closing of stomata and
induces
leaf senescence. Gibberellins, primarily gibberellic acid, are involved in
breaking
dormancy in seeds and in the stimulation of cell elongation in stems.
Gibberellins
are also known to cause dwarf plants to elongate to normal size. Cytokinins,
e.g.,
zeatin, are produced primarily in the roots of plants. Cytokinins stimulate
growth of
lateral buds lower on the stem, promote cell division and leaf expansion and
retard
plant aging. Cytokinins also enhance auxin levels by creating new growth from
meristematic tissues in which auxins are synthesized. Auxins, primarily indole-
3-
acetic acid (IAA) promote both cell division and cell elongation, and maintain
apical
dominance. Auxins also stimulate secondary growth in the vascular cambium,
induce the formation of adventitious roots and promote fruit growth.
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[003] Auxins and cytokinins have complex interactions. It is known that the
ratio of auxin to cytokinin will control the differentiation of cells in
tissue cultures.
Auxin is synthesized in the shoot apex, while cytokinin is synthesized mostly
in the
root apex. Thus, the ratio of auxin to cytokinin is normally high in the
shoots, while it
is low in the roots. If the ratio of auxin to cytokinin is altered by
increasing the
relative amount of auxin, root growth is stimulated. On the other hand, if the
ratio of
auxin to cytokinin is altered by increasing the relative amount of cytokinin,
shoot
growth is stimulated.
[004] The most common naturally occurring auxin is indole-3-acetic acid
(IAA). However, other synthetic auxins, including indole-3-butyric acid (IBA);
naphthalene acetic acid (NAA); 2,4-dichlorophenoxy acetic acid (2,4-D); and
2,4,5-
trichlorophenoxy acetic acid (2,4,5-T or agent orange) are known. While these
are
recognized as synthetic auxins, it should be acknowledged that IBA does
naturally
occur in plant tissues. Many of these synthetic auxins have been employed for
decades as herbicides, producing accelerated and exaggerated plant growth
followed by plant death. Agent orange gained widespread recognition when it
was
used extensively by the United States Army and Air Force in deforestation
applications during the Vietnam War. 2,4-D finds continuing use in a number of
commercial herbicides sold for use by the home gardener.
[005] Compounds are classified as auxins based on their biological activity in
plants. A primary activity for classification includes simulation of cell
growth and
elongation. Auxins have been studied since the 1800's. Charles Darwin noticed
that
grass coleoptiles would grow toward a uni-directional light source. He
discovered
that the growth response of bending toward the light source occurred in the
growth
zone below the plant tip, even though it was the tip that perceived the light
stimulus.
Darwin suggested that a chemical messenger was transported between the plant
tip
and the growth zone. That messenger was later identified as an auxin.
[006] All plants require a certain ratio of auxin, i.e., IAA, to cytokinin for
cell
division. While the ratios may vary, it is well known that the ratio of IAA to
cytokinin
must be much greater for cell division in the apical meristem tissue than the
ratio in
the meristem tissue of the roots. Each part of a plant may require a different
IAA to
cytokinin ratio for cell division. For example, different ratios may be
required for cell
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division in the stem, fruit, grain and other plant parts. In fact, it has been
estimated
that the ratio for apical meristem cell division may be considerably more, in
fact, as
much as 1000 times greater than the ratio necessary for root cell division.
While the
mechanism by which this ratio is determined remains unknown, other hormones
and
enzymes are likely to be involved in its perception.
[007] Plants generally grow best at temperatures from about 68 F to about
87 F (about 21 - 30 C). In this temperature range it is presumed that plants
produce sufficient amounts of auxins, particularly IAA, to maintain normal
growth.
While ideal temperatures vary among species, crop plants typically grow best
in the
foregoing range. While temperature is an important factor, it should also be
noted
that other environmental factors can effect cell division. The moisture
content of the
plant, the nutrient status (especially the level of available nitrogen), the
light intensity
on the plant and the age of the plant, together with the temperature, all
effect the
ability of the plant to produce plant hormones, including IAA and cytokinin
which
dictate cell division.
[008] As the temperature rises above about 90 F (above about 31 C) or
falls below about 68 F (21 C) plant growth and cell division slow. As the
temperature further increases above about 90 F and drops below about 68 F,
the
production of IAA and other plant hormones decreases at an accelerating rate.
Thus, it becomes difficult, if not impossible, to achieve new cell growth at
temperatures above about 100 F. Similarly cell division slows and then ceases
as
temperatures plunge significantly below about 68 F. During normal growing
conditions with adequate moisture and temperature, i.e., temperatures between
about 70 F and 90 F, the plants will produce an abundance of IAA. Cell
division
may be further impeded by other inhibitive compounds produced by IAA and other
plant hormones. As temperatures increase above about 90 F or below about 68
F,
the ability of plants to produce IAA rapidly diminishes.
[009] Plants respond to light during the growth process. The light in the
range of the red wavelengths is primarily used by plants in order to trigger
normal
plant growth. It also determines the plant's photoperiodism. When plants are
spaced at relatively high density in a field, red wavelength light is reduced
on plant
parts by the shading effect of neighboring plants. This causes the shaded
plant to
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seek out more sunlight and causes the extension of internode length as the
shaded
plant rapidly grows to seek more sunlight. It is well known that auxin
(particularly
IAA) moves from the light side of plant tissue to the dark side. When shading
of
lower plant parts becomes prominent in a field of plants, the movement of IAA
from
the new apical meristem tissue rapidly accelerates downward in the plant. The
movement of IAA downward will be dependent upon the amount of shade that
occurs
at the bottom of the plant.
[010] Since gibberellic acid tends to migrate in a plant to where there is the
most abundance of red wavelength light, it will tend to move upward in a plant
toward the apical meristem tissue. This, in turn, triggers the more rapid
movement
downward of IAA toward the shaded side of the plant. The amount of movement of
IAA downward will depend upon the positioning of the apical meristem tissue of
the
plant. If the apical meristem tissue is located more vertically from the plant
crown,
IAA movement downward will be greater. If the apical meristem tissue is
located
more horizontally relative to the plant crown, IAA movement will be less. If
the apical
meristem tissue on a branch or a limb is bent downward, it is very difficult
for IAA to
move against gravity and therefore its movement downward will be limited.
[011] When plants are rapidly growing under conditions that include ample
moisture, ideal temperatures and ample amounts of nitrogen fertilizer, auxins
are
efficiently transported out of the tissues where they are metabolized and move
downward in the plant. This results in the redistribution of auxin and the
reduction of
the auxin level in the tissues where it was produced. The result is tissues
that are
deficient in the level of auxin.
[012] The present invention is based upon the Stoller model for plant growth.
This model was developed from a combination of field observations and analysis
of
the scientific literature. This model takes into account published data on
plant
hormone levels and relates them to plant growth that can be observed to result
from
changes in these hormone levels. Although much research has been done over the
past century on plant hormones, this is to our knowledge the first
comprehensive
model relating levels of hormones directly to field-observed plant growth
responses.
This model also provides for the first time an applicable method for
controlling plant
growth in the field with natural plant hormones to generate desired growth.
Although
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there is a broad research base in the literature, most of this research deals
with only
one hormone or the specifics of the interaction of a subset of hormones within
a very
defined event. In addition most of this published work has been done in the
laboratory on model plants, or has been done in vitro in excised or disrupted
plant
tissues. Never before has a model been published that relates the wide array
of
hormone responses to one another within developmental events with an eye to
altering these responses to affect crop production by generating more ideal
growth.
[013] Ideal plant growth is defined as growth that would occur under
conditions of ideal temperature, moisture, light, and nutrient balance, and is
represented by adequate growth of both root and shoot tissues such that the
growth
of one tissue does not dominate at the expense of another tissue during any
growth
stage. During ideal growth a plant is neither infected by pathogens nor
invaded by
insects or parasites. An ideally growing plant is generally compact in
appearance,
with equal amounts of root and shoot mass, good color, and good flower and
fruit
set. An ideally growing plant will give the maximum yield possible from its
genetic
potential.
[014] There is a remarkable uniformity of boron requirements and/or boron
deficiency symptoms across plant and crop species. The youngest growing
tissues
are always affected first and in all cases root growth is rapidly impaired.
These are
the tissues in plants whose regulation and development is also controlled
largely by
plant hormones. Boron should extend the life and, therefore, the effectiveness
of
IAA by reducing the breakdown of IAA by IAA -oxidase. Boron has also been
shown
to increase polyamines, putrescine, spermidine, ascorbic acid, spermine, and
the
plant hormones, IAA and gibberellic acid. Thus, there is an important
interaction/enhancement or synergism between hormones, especially auxin, and
boron and other minerals in physiological activity. For example, boron appears
to
have a direct effect on transport of the plant hormone auxin, possibly by the
movement of auxin in and out of cells.
[015] Boron has been shown to be essential for nitrogen fixation by plants,
where it enhances the stability of the interconnections between the nodules
and the
plant roots. Moreover, from an evolutionary standpoint boron-regulated growth
may
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be correlated with the ability of vascular plants to maintain upright growth
and to form
lignified secondary walls.
[016] Boron deficiency and toxicity inhibit ATPase-dependent hydrogen
pumping and ATPase activity in sunflower roots and elicit proton leakage from
cells.
Thus, membrane activity is strengthened with sufficient and appropriate boron
levels
through more effective ATPase activity and controlled conductance across the
plasma membrane. Borate compounds can inhibit calcium-stimulated ATPase
activity as well as store-operated calcium entry channels. Boron enhances
phosphorylation and, therefore, signals transduction, including hormone
transduction, probably through a mediator whose transduction signals involve a
cascade of phosphorylations. It has been reported that boron deficiency
reduces
oxidative damage to cells and that ascorbate and glutathione levels decrease
dramatically with boron deficiency. It has also been suggested that the
oxidative
damage from boron deficiency is the result of impaired cell wall structure.
[017] Through its effect on proton secretion and on the activity of the plasma
membrane NADH oxidase, boron may be directly associated with cell growth. An
aploplastic target for the primary action of boron deprivation which signals
deeper
into the cell via endocytosis-mediated pectin along a putative cell wall
plasma
membrane cytoskeleton continuum has also been suggested. Boron in animals can
act both at the transcriptional and translational level. Further research will
likely bear
out similar action in plants. Boron is taken up by the plant and accumulates
at the
growing points where it enters the cell walls. Ninety (90) per cent of boron
in a plant
is in the cell walls in the pectin fraction referred to as the
rhamnogalacturonan region
where it may be involved in cell to cell adhesion and therefore cell signaling
for
effective plant growth. Pollen germination is especially sensitive to boron
deficiency.
It has been suggested that boron has an important role in ionic membrane
transport
regulation. Boron appears to be most active in the G2/M phase of the cell
cycle, i.e.,
just before and during mitosis when cells divide.
[018] Further derivatives of boron have been reported to have anti-fungal
and anti-bacterial activities. Those activities may be strengthened in
combination
with plant growth regulators, in particular auxin.
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[019] Those skilled in the art have longed sought environmentally friendly
methods for improving plant growth and crop productivity while also improving
the
resistance of plants to pathogens and insects. Thus, there has been a long
felt, but
unfulfilled need, for such methods. The present invention solves those needs.
SUMMARY OF THE INVENTION
[020] This invention provides a model for understanding the ways hormones
function in crop plants, and provides methods by which plant growth can be
manipulated through the addition of hormone solutions through application to
roots
or aerial tissues. The method relies on the observation that the root of the
plant is
the primary organ responsible for sensing environmental conditions and sending
hormone cues. Central to the invention is the observation that hormone
responses
are determined chiefly by the establishment of auxin and cytokinin gradients
within
the plant. It is the relative levels of hormones to one another and to auxin
and
cytokinin that are the determining factors for most hormone responses. By
altering
the hormone ratios within tissues through the application of one or more plant
growth
regulators, preferably auxin and/or cytokinin, we can alter plant growth
responses.
[021] The present invention is directed to methods for improving the growth
and crop productivity of plants by adjusting the level or ratio of plant
hormones in the
tissues of the plant. In the methods of the present invention, a plant hormone
in an
amount effective to produce the desired effect, e.g., improved growth,
improved fruit
set, or improved plant architecture, is applied to the plant tissue.
Improvements to
plant architecture may include more prolific and continuous root growth;
shorter
stature with shorter internodes; stalkier, more branching shoot configuration;
thicker
leaves with enhanced photosynthetic capacity and enhanced sugar
(photosynthate)
transfer to the anatomic, crop portions having economic interest to the
producer;
even, continuous and enhanced cell division and cell expansion resulting in
improved number and quality of flower pollination, fruit initiation, fruit
sizing and
compositional development; or similarly, enhanced tuber, seed, stem or leaf
development and performance with concomitant enhanced qualities in shipping,
storage or merchandising. While any of the plant hormones may be effective,
the
hormone is typically selected from the auxins, cytokinins, gibberellins and
abscisic
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acid. The presently preferred hormone is an auxin, particularly indole-3-
acetic acid
(IAA) or indole-3-butyric acid (IBA). However, the auxin is applied in an
amount
insufficient to negatively affect growth of the plant tissues. Alternatively,
other plant
growth regulators (PGRs), which act by altering the level, ratio or
effectiveness of
endogenous or applied hormones, may be used.
[022] The auxin is selected from the group consisting of the natural auxins,
synthetic auxins, auxin metabolites, auxin precursors, auxin derivatives and
mixtures
thereof. The preferred auxin is a natural auxin, most preferably indole-3-
acetic acid.
The presently preferred synthetic auxin is indole-3-butyric acid.
Alternatively,
manipulation of the auxin level within the desired range can be achieved by
application of a plant growth regulator or hormone, e.g., cytokinin or
gibberellic acid.
[023] In the methods of the present invention, a hormone, e.g., an auxin or
another PGR, is applied to the seed or tubers of the plant prior to planting.
Alternatively, the auxin or PGR is applied to the roots, foliage, flowers or
fruits of the
plant after planting. When applied to the seed or tubers, auxin is preferably
applied
at a rate of about 0.0028 to about 0.028 grams auxin per 100 kg. seed weight.
When applied to potato seed pieces, the rate of application may be calculated
so as
to result in about 0.0125 to about 2.8 grams auxin per hectare of planted
pieces.
When applied to the roots, foliage, flowers or fruits of plants, the auxin
should be
applied at a rate of about 0.0002 to about 0.06 grams auxin per hectare per
day.
Multiple applications may be required over an extended growing period.
[024] The hormone, e.g., an auxin or another PGR, may be applied as an
aqueous solution or as a powder. When applied as an aqueous solution, the
solution may be applied to the plant tissue by conventional spraying or
irrigation
techniques. The solution may further include a metal selected from the group
consisting of the alkaline earth metals, transition metals, boron and mixtures
thereof.
Such metals preferably are selected from the group consisting of calcium,
magnesium, zinc, copper, manganese, boron, iron, cobalt, molybdenum and
mixtures thereof. Seeds or tubers may be treated prior to planting by spraying
with
or by immersion in such aqueous solutions. The preferred method of applying
PGRs
may be along with a boron-containing solution. Boron will stabilize the auxin
in plant
tissues to which such solutions are applied.
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[025] The application of a metal, preferably boron, together with the PGR
appears to extend the effective life of the PGR, thus permitting longer times
between
repeat applications. Boron appears to improve the efficacy, both the life and
activity,
of added IAA by suppressing the activity and or synthesis of IAA-oxidase, the
enzyme that degrades IAA in plants. The anti-oxidant ascorbic acid may be part
of
the mechanism through which boron enhances IAA activity. Boron also enhances
sugar transport in plants, cell wall synthesis, lignification, cell wall
structure through
its borate ester linkages, RNA metabolism, DNA synthesis, phenol metabolism,
membrane functions and IAA metabolism. Further, boron is known to modulate
respiration. The boron requirement for reproductive growth is higher than that
for
vegetative growth. Boron interacts with auxin especially in cell elongation
such as
pollen tubes, trichomes and other cells. Boron also stimulates auxin-sensitive
plasmalemma NADH-oxidase and is necessary for the auxin stimulation of
ferricyanide-induced proton release in plant cells. Boron is also part of the
endocytosis mechanism of rhamnogalacturonan II dimers (linking through di-
ester
bonds) in formation of primary walls in dividing cells such as root tips,
trichomes or
pollen tubes. Thus, boron is linked with auxin-mediated cell division as well
as
auxin-mediated cell elongation. Finally, boron has been reported to have anti-
fungal
and anti-bacterial activities. Accordingly, it is believed that application of
PGRs,
together with boron, will improve the effect of the PGR in suppressing insect
and
pathogen infestation in plants.
[026] The hormone, e.g., an auxin or other PGRs, may also be applied as a
dry powder. In such applications, the hormone is mixed with an environmentally
and
biologically compatible material. The powder may be applied to the foliage,
flowers
or fruits of the plant by conventional dusting methods. Alternatively, the
powder may
be encapsulated in a biologically compatible material to provide slow release
when
placed on or near the seeds, tubers or roots of the plant. Exemplary
biologically
compatible materials include the clays, lignites, resins, silicones and
mixtures
thereof.
[027] The methods of the present invention improve plant architecture, e.g.,
by limiting excessive growth of vines, by controlling internode length, by
controlling
top growth, by controlling flower set, by increasing fruit size and/or by
increasing total
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crop yield. These improvements are achieved by applying an effective amount of
a
hormone, preferably an auxin, to the plant tissue.
[028] Finally, the present invention includes seeds and seed pieces for
producing plants having dispersed on the surface thereof a hormone, e.g., an
auxin
or other PGR, in an amount effective to alter plant architecture as explained
above,
but in an amount insufficient to negatively effect growth of the plant
tissues.
Alternatively, a plant growth regulator, e.g., a plant hormone such as
cytokinin or
gibberellic acid, which acts by affecting the level or effectiveness of
applied auxin
may be used. Such PGR should be dispersed on the surface of seeds or seed
pieces in an amount effective to manipulate the auxin level within the desired
range.
[029] The methods of the present invention have been found to improve the
growth and productivity of plants by altering plant architecture as explained
above.
Significantly, these improvements have been achieved without the use of
environmentally hazardous chemicals. The methods to the present invention
achieve these improvements by applying naturally occurring or synthetic plant
hormones to adjust the hormone levels and ratios within the plant tissues to
produce
the desired results. Thus, the long felt, but unfulfilled need for
environmentally
friendly methods for enhancing plant growth and productivity have been met.
These
and other meritorious features and advantages of the present invention will be
more
fully appreciated from the following detailed description and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[030] Other features and intended advantages of the present invention will
be more readily apparent by reference to the following description in
connection with
the accompanying drawings wherein:
[031] FIG. 1 is a graph illustrating the level of various plant hormones
present in plant tissue during the plant growth cycle;
[032] FIG. 2 is a graph illustrating the gradient of auxin to cytokinin in
plant
tissue between the roots and the shoots of the plant;
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[033] FIG. 3 is a bar graph illustrating the effect on hypocotyl length
resulting
from treatment of radish plants with various plant hormones in accord with the
present invention as summarized in Table I;
[034] FIG. 4 is a bar graph illustrating the effect on leaf length resulting
from
treatment of radish plants with various plant hormones in accord with the
present
invention as summarized in Table I;
[035] FIG. 5 is a bar graph illustrating the effect on average shoot height
resulting from foliar applied treatment of radish plants with various plant
hormones in
accord with the present invention as summarized in Table II;
[036] FIG. 6 is a bar graph illustrating the effect on the average total fruit
weight of tomatoes produced from plants treated with various plant hormones in
accord with the present invention as summarized in Table III;
[037] FIGS. 7 is a bar graph illustrating the effect on the average fruit
weight
of individual tomatoes produced from plants treated with various plant
hormones in
accord with the present invention as summarized in Table III;
[038] Fig. 8 is a bar graph illustrating the length of, respectively, the
first,
second and third internodes resulting from treating cucumber plants with
different
plant hormones, either alone or in combination, in accord with present
invention as
summarized in Table IV;
[039] Figs. 9a - 9e are bar graphs illustrating, respectively, the average
vine
length, average internode number, average number of branches, average
internode
length and average fruit length of cucumber plants treated with various plant
hormones in accord with the present invention as summarized in Table V;
[040] Figs. 10a - 10c are bar graphs illustrating, respectively, the average
plant height, canopy diameter and root weight of pepper plants treated with
various
dosage rates of a plant growth regulator solution in accord with the present
invention
as summarized in Table VI; and
[041] Figs. 11 a and 11 b are bar graphs illustrating, respectively, the
average
yield per plant and percentage of peppers graded large / fancy from pepper
plants
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treated with various dosage rates of a plant growth regulator solution in
accord with
the present invention as summarized in Table VII.
[042] While the invention will be described in connection with the presently
preferred embodiments, it will be understood that it is not intended to limit
the
invention to those embodiments.
DETAILED DESCRIPTION OF THE INVENTION
[043] Plant hormones during Development
The Stoller model for plant growth states that plant growth is a direct
response to hormone signals and hormone balance, and this balance is dynamic,
changing with plant age and in response to environmental conditions such as
temperature, moisture, nutrient balance, and light. Early in seed formation,
cytokinin
levels briefly rise to a maximum level, and this rise coincides with a period
of rapid
cell division (Lur and Setter 1993). This is followed by a rise in auxin,
gibberellin and
abscisic acid levels (Marschner 1986). In the beginning stages of plant growth
following seed inhibition, cytokinin is the first hormone produced. This is
perhaps
most obvious through the observation that during seed germination, the
radicle, or
seedling root, is the first structure to emerge from the seed coat. The root
is the
primary site of cytokinin biosynthesis (Davies 1995). Cytokinin then moves
from the
root tip upward into the shoot, and establishes a gradient in which cytokinin
is high in
root tips and decreases gradually toward the shoot apex. Once cytokinin has
reached the shoot apex, cell division is stimulated. These new shoot tissues
produce auxin, and this auxin is the dominant hormone in young shoot tissues
(Davies 1995). During this stage, cell division and therefore growth is
directly
correlated to the relative amounts of auxin and cytokinin in the tissue, as
the length
of time cell division will occur is dependent on the relative amounts of these
hormones. When levels in the tissue are adequate, cell division will occur.
When
levels of one or both of these hormones decrease below a critical ratio, cell
division
will cease. If hormones can be added to tissues at this time, the period of
cell
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division can be prolonged. This will potentially increase cell number and,
therefore,
size of plant tissues.
[044] The auxin produced in the new shoot tissues travels down the stem to
the roots, where it stimulates cell division to generate lateral root growth.
As auxin is
transported out of shoot tissues, it stimulates the synthesis of gibberellic
acid (GA).
Therefore, after the stage of cell division, gibberellin levels begin to rise
in the tissue
while cytokinin and auxin levels fall (Marschner 1986). If auxin transport
does not
occur, gibberellic acid biosynthesis will not occur (Wolbang and Ross, 2001).
While
auxin seems to be most responsible for the expansion of leaf cells,
gibberellic acid
plays an important part in the elongation of stem cells (Fosket 1994). A high
level of
auxin transport downward will generate greater biosynthesis of gibberellic
acid, and
thus longer internode length. Gibberellic acid also causes elongation of
stolons in
potato, and high gibberellic acid levels in potato stolons will prevent
tuberization.
During this period in which gibberellin dominates, cell size increases. See
Fig. 1.
[045] Toward the end of cell sizing, ethylene and abscisic acid (ABA) levels
rise and cell maturity is reached. The auxin that was synthesized during the
cell
division stage stimulates not only gibberellic acid production, but also
ethylene
biosynthesis. Ethylene in turn stimulates ABA biosynthesis (Hansen and
Grossman
2000). Ethylene and abscisic acid levels are responsible for tissue maturation
and
will eventually trigger senescence and death, once auxin, gibberellin and
cytokinin
levels decrease (Pessarakli 1994).
[046] In addition to normal production during development, ethylene and
abscisic acid can also be synthesized in response to plant stress. Often times
a
surge of reactive oxygen species coincides with increased ethylene (Abeles, et
al.,
1992). Abscisic acid and ethylene mediate several events associated with
senescence and fruit ripening. Abscisic acid causes stomatal closure resulting
in
decreased carbon dioxide exchange and decreased photosynthesis, and abscisic
acid inhibits sucrose mobilization by preventing phloem loading (Davies 1995).
In
addition several other events follow the increase in ethylene and abscisic
acid during
senescence and ripening including chloroplast breakdown, increased
respiration,
and protein and DNA degradation (Abeles et al 1992).
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[047] Sites of Hormone Synthesis and Distribution
Cytokinin is produced in meristematic tissues, primarily in the root, and
can be transported to other tissues through the xylem and phloem
(Pessarakli,1994).
Auxin is also produced in meristematic tissues, especially in shoots. Auxins
can be
transported downward through parenchyma cells via the action of polar auxin
transporters, or can be transported in any direction through sieve tubes of
the
phloem (Pessarakli,1994). Gibberellins are produced in growing tissues, with
the
highest concentrations of gibberellic acid being in roots and developing
seeds, and
lower concentrations in shoots and leaves. Gibberellic acid can be transported
through both the xylem and the phloem. Abscisic acid is produced in all
tissues and
is transported to growing regions through either xylem or phloem. Ethylene is
synthesized in all tissues and moves rapidly by diffusion (Pessarakli,1994).
[048] Plant Hormone Interactions
The growth of the plant is clearly a complex of responses to the
interactions of many hormones. As stated earlier, it is well documented that a
high
cytokinin to auxin ratio will favor shoot development while a low cytokinin to
auxin
ration will favor root development (Pessarakli,1994). These hormones also
regulate
the levels and possibly the transport of one another. Indole-3-acetic acid
(IAA) can
alter cytokinin levels and vice versa (Zhang et al 1996). In addition, other
hormones
affect the synthesis, degradation, and transport of one another. Gibberellic
acid
stimulates IAA oxidase activity to bring down IAA levels following the cell
division
stage. It is known that gibberellic acid can stimulate it's own biosynthesis
through the
repression of negative regulators of transcription (Gazzarrini and McCourt,
2003),
and that IAA is required for gibberellic acid biosynthesis (Wolbang and Ross
2001).
IAA has also been shown to stimulate the production of ethylene, and ethylene
causes an increase in abscisic acid synthesis (Hansen and Grossman 2000).
[049] In addition to regulating the levels of one another, the hormones also
interact to affect plant processes as determined by the ratio of one hormone
to
another. High levels of abscisic acid and ethylene in young leaves will not
induce
senescence, and in young leaves auxin, gibberellic acid, and cytokinin levels
are still
relatively high. However in mature leaves, where auxin, gibberellic acid, and
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cytokinin levels have dropped, abscisic acid and ethylene do promote
senescence.
Thus, by changing the timing of the hormone fluxes in tissues, it is possible
to
change the timing of developmental events such as senescence.
[050] Hormones also affect the transport of metabolites in the plant. Sucrose
and gibberellic acid move in the opposite direction of IAA. In other words, in
tissues
where IAA levels are being reduced, either due to transport or degradation,
gibberellic acid levels and subsequently sucrose levels rise. The mechanisms
by
which this process is mediated are unknown, but the transport of auxin
conjugates
appears to be involved in phloem loading (Davies 1995).
[051] It is also interesting to note that many of the mineral nutrients
associated in plant deficiencies are minerals involved in auxin metabolism.
For
example, zinc is a cofactor in auxin biosynthesis, and boron inhibits the IAA-
oxidizing
enzyme, thereby extending the half-life of IAA. Calcium is involved in auxin
transport
and auxin signaling pathways, and manganese and magnesium are cofactors for
enzymes that liberate auxin from conjugate storage forms. Again, altering the
nutrients that affect auxin content can skew the hormone balance and change
the
development of the plant.
[052] While these interactions are complex and there are intensive areas of
research on subsets of these interactions, we note one unifying factor.
Relative
levels of auxin and cytokinin to the other hormones seem to be central in the
interaction of these hormone signals. While the mechanisms of plant hormone
signaling pathways are unknown, the fact remains that an alteration of auxin
or
cytokinin levels will potentially alter these hormone interactions.
[053] Photosynthate Movement
Photosynthates in a plant normally move in an opposite direction to the
IAA gradient. When a plant is growing in a normal condition, IAA is produced
in the
apical meristem tissue and moves, by gravity, toward the basal part of the
plant.
When doing so, it directs the movement of photosynthates from mature leaves
toward the apical meristem tissue of the plant. The rapid growth of a plant is
merely
an indication of the quantity of photosynthates that are moving from mature
leaves to
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the apical meristem tissue of the plant. This would also indicate that the
gradient of
IAA movement downward increases as the rapidity of growth of the plant
increases.
[054] In most crops, movement of photosynthates toward the basal part of a
plant are even more desirable than the movement of photosynthates to the
apical
meristem tissue. Some examples of this are potatoes, beets, onions and other
crops
with storage tissue that develop on the lower end of the plant. Perhaps, more
importantly, the needs of roots for photosynthates are critical for the
survival of a
plant. As a plant tends to grow more rapidly, the root mass of a plant tends
to
decelerate in growth. This is primarily due to the lack of movement of
photosynthates to the apical meristem tissue. This is particularly true for
rapidly
growing plants such as corn, bananas, cotton, soybeans and many other plants
that
make rapid vertical growth.
[055] If one could decrease the gradient of IAA movement from the apical
meristem tissue to the roots, then the sink of the roots and/or developing
fruit on a
plant would have a much greater capability of competing for photosynthates
with the
apical meristem tissue. In other words, if the gradient of IAA movement from
the
apical meristem tissue downward could be reduced, there would be greater root
growth and fruit growth accompanied by uninterrupted supply of photosynthates
to
those tissues.
[056] The reduction of IAA gradient and the consequent increase of root and
fruit mass can be obtained by either the application of IAA and/or IBA in a
constant
supply to the roots so that the gradient of these two auxins moving upward in
a plant
is greater than the gradient of the natural occurring IAA produced at the
apical
meristem tissue to move down in the plant. This has been demonstrated through
research trials on onions, peppers, corn and soybeans. Applications of these
hormones are normally made on a weekly or bi-weekly schedule. This does not
mean to imply that a greater frequency would not be preferable.
[057] Another way to decrease the IAA gradient is a topical application of IAA
and/or IBA to the upper portions of the plant. This would tend to equalize to
the level
of IAA and/or IBA in all of the above ground plant tissue. When obtaining a
high
level of IAA and/or IBA in the above plant tissue, the gradient of IAA is
neutralized.
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This can be more effectively done with short intervals, e.g., two to three
days,
between these topical applications. Alternatively, these two auxins can be
added,
together with a boron solution, to maintain the activity of the IAA and/or IBA
over a
longer period of time. This is probably the preferred method of using IAA
and/or IBA
in regulating IAA gradient movement, because it eliminates more frequent
applications and the costs associated therewith.
[058] Tests involving the consistent application of IAA and/or IBA to corn
plants through a drip irrigation system were conducted at Texas A&M
University.
Also, tests involving the topical application of IAA and/or IBA were conducted
on
corn trials at Texas A&M University. Both of these trials produced
significantly
increased corn yields. It was noted that the root mass and the stalk diameter
of the
corn plants were much greater where these two methods of application of IAA
and/or
IBA were applied to the corn plant.
[059] One must realize that a corn stalk is merely made up of the basal
portion of the corn plant leaves. Increasing the stalk diameter is an
indication that
more photosynthates are moving from the leaves down to the basil portion of
the
leaves. This would be reflected by an increase in the diameter of the stalk.
This is
exactly what is noted when the above two methods of applying IAA and/or IBA
were
tested with corn plants.
[060] By being able to reverse the direction of photosynthate movement in a
plant while it is growing, both larger roots and fruits should be produced.
This is
exactly what happened in the Texas A&M University experimental trials on
onions,
peppers and corn. The control of photosynthate movement within the plant by
the
administration of IAA and/or IBA is a revolutionary concept and application
for
counteracting the hormonal activity which is normally due to light sensitivity
and the
effects of gravity on a growing plant.
[061] Hormonal Changes in Plants
Every plant tends to follow the same characteristic hormonal shifts as it
goes through various stages of growth. When a seed is planted the hormonal
shift is
from abscisic acid (ABA) which causes seed dormancy toward gibberellic acid
and/or
auxin. This is an enzyme related activity, which causes the germination of the
seed
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under proper moisture and temperature conditions. The first tissue that
usually
appears from the seed is the root.
[062] Roots have the ability to synthesize cytokinin. Their ability to
synthesize auxins is rather low. Therefore, in order to have adequate cell
division
the roots must receive a supply of IAA from the apical meristem tissue of new
growth. It is a demand from the roots for additional IAA that forces the
growing point
and new leaves from a plant. New cell growth provides IAA to be transported
downward to apical tissue of the root in order to trigger cell initiation and
cell division.
If the demand for IAA by the root system is greater then the upper portion of
the
plant can furnish, the root will trigger bud formation of new plants, which
originate
from the crown or the basal portion of the plant. This is manifested by
suckering on
corn, daughter plants on bananas, tillers on wheat, and vegetative stolons on
potatoes.
[063] As a plant undergoes its rapid growth stage, the bottom portion of the
plant is shaded. This effect of light differential causes a more rapid
movement of IAA
in the apical meristem tissue of a plant downward toward the basal portion of
a plant.
This, in turn, initiates movement of gibberellic acid upward to the apical
meristem
tissue of the plant, resulting in increased internode length.
[064] When the downward movement of IAA gradient increases, many
vegetative and reproductive buds remain in dormancy. Dormancy of these buds
will
not be released until the gradient of the downward IAA movement in the plant
is
reduced. Therefore, when a plant is growing rapidly many of the buds of the
main
sterns are inactive. It has often been observed that a rapidly growing plant
tends to
have reduced flowering and vegetative bud initiation.
[065] When the plant begins its reproductive cycle, i.e., flowering, the ratio
of
auxin to cytokinin is rapidly changed. During this period, the demand by the
buds for
auxin in order to accomplish cell division is high. The gradient of downward
auxin
movement in the plant can be significantly reduced, producing a curvature of
the
roots downward. This will also decrease the downward IAA gradient so that
fruits
are more capable of competing for photosynthates from mature leaves. This is
important in order to provide a constant supply of photosynthates to the
developing
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fruits. If this is not accomplished, many physiological disorders occur in the
fruits
during the period of development. During this period of fruit development, the
fruit is
constantly competing as a sink for photosynthates with the apical meristem
growing
tissue. It is important during this period that the competition of the apical
meristem
tissue for photosynthate sink is reduced compared to the sink of the fruit.
[066] It is well known that multiple fruiting on a plant part such as a tomato
truss or soybean raceme constantly compete for photosynthate supply. This is
also
common when noticing the fruit sizing on any cucurbit. The larger fruit is the
more
dominant fruit. It sizes at the expense of the fruit that are put in positions
further
away from the crown or the stem of the plant. This sequential sizing is caused
by
IAA dominance of the larger fruit over the small ones. This sequential sizing
can be
reduced through the application of an IAA and/or IBA material directly to the
fruiting
areas. This will enable the later sizing fruit to compete more favorably with
those
that size earlier. The reduction of sequential sizing is very important in
trying to
obtain uniformity of fruit, tubers and other reproductive plant parts.
[067] During the period of ripening the combination of ethylene and ABA tend
to dominate the plant cell, resulting in cell senescence. This senescence of
plant
cells in individual plant parts is normally referred to as ripening.
[068] As can be seen from the above comments, different ratios of hormones
are needed at different stages of growth. It is almost impossible to know
exactly the
ratio of various hormones in different plant species at different periods of
growth. It
is, therefore, proposed that auxin, cytokinin and/or gibberellic acid be
applied in
abundance at regular intervals to enable the plant to balance its own hormonal
needs. This is critical to the use of plant growth hormones in order to
control and
increase the yield of crops. This is particularly important in obtaining the
maximum
genetic expression from any of the plant cells that are developing during any
period
of the plant's growth cycle.
[069] In order to inhibit the effects of light (particularly red wavelength)
it is
necessary to control the movement of gibberellic acid inside the plant. This
can be
done by either using a gibberellic acid inhibitor or maintaining the stability
of IAA in
the apical meristem tissue, which in effect, regulates the activity of
gibberellic acid
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that moves to the apical meristem tissue. The latter can be done by
administering
auxin (particularly IAA or IBA) to the upper part of the plant in such
quantities or with
another compound, which will maintain auxin concentration over a longer period
of
time. When doing so, the dominance of gibberellic acid in the plant cell is
greatly
retarded by the abundance of IAA in the apical meristem tissue.
[070] The use of IAA as a topical application or applied through the root
system with regular abundance can control the activity of gibberellic acid and
thereby
control the growth of the plant during periods of plant shading due to high
plant
population, or in case of a tree, the shading of the internal parts of the
plant by the
leaves of the tree.
[071] The Function of Hormones in Tissues
The function of the root is to provide the nutrients, minerals, and water
needed by the plant to survive and reproduce. The Stoller model also assumes
that
the root is the primary sensing organ of the plant, with the root cap
functioning as a
"thinking cap" to gather information about the outside conditions and
communicate
these conditions to other parts of the plant to initiate a response within the
plant.
There is a great deal of evidence for this theory. Numerous studies on
gravitropic
and touch responses have implicated the root cap in determining the direction
in
which the root should grow (Massa and Gilroy 2003, Boonsirichai, et al. 2002).
Other studies, including some by Darwin, implicate the root cap in sensing
other
stimuli such as water potential (Eapen et al. 2003). The root cap is likely
the region
of the plant most responsible for sensing environmental conditions and
altering the
hormone balance of the plant accordingly. It has been shown that signals from
the
root cap can stimulate the formation of an auxin gradient in the root
(Boonsirichai et
al. 2002, Chen et al. 2002), and that this auxin gradient results in root
bending to
alter the direction of root growth. It is likely that root cap signals may be
carried
throughout the plant to alter the gradients of many hormones and affect growth
according to the environment the root caps perceive. The Stoller model takes
advantage of the role of the root cap in generating hormone signals through
the
application of plant hormones to the root area. Root application will be the
preferred
method of hormone application because it gives more consistent plant response
due
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to the fact that the root cap is the growth control center as well as the
natural source
of many hormone signals.
[072] The function of the shoot is to provide energy for growth through
photosynthesis, and to carry out reproductive processes. The shoot grows
primarily
in response to the conditions communicated from the root. The communications
are
likely perceived as a difference in the ratio of hormones to one another. The
result of
this communication is an alteration of growth. For example, if root growth has
been
prolific, the amount of cytokinin produced in new root tissues will be higher
relative to
levels when there is less growth. This cytokinin level will result in a change
in the
gradient of auxin to cytokinin that will increase the cytokinin content in
aerial tissues
and stimulate new cell growth. See Fig. 2. The greater the root mass, or the
stronger the cytokinin production, the more shoot growth will be stimulated.
Thus, a
high amount of cytokinin in roots during the vegetative growth stage can
sometimes
lead to excessive growth of vines in potato, and can also stimulate the
production of
lateral branching in dicots. During this vegetative period, the addition of
auxin to the
root area will prevent this unwanted top growth.
[073] IAA synthesized in new shoot tissues can then be transported to the
root, or can be diverted to any tissue along the way. High IAA concentrations
are
also critical to bud development of flowers and fruit development. This is
evidenced
by the fact that when temperatures are very high during flower set and fruit
set, there
is a high rate of flower abscission and fruit malformation. This results
because IAA
synthesis is inhibited at higher temperatures (Rapparinini, et al 2002)
possibly due to
the temperature optima of the nitrilase genes involved in IAA biosynthesis
(Vorwerk
et al., 2001). When plants make the transition to flowering, new flower
tissues
generate a large supply of auxin. This auxin is then transported out of the
flower. As
fruit and seed develop, these tissues, too, synthesize high levels of IAA,
which is
transported out.
[074] This auxin transport causes several things to happen. First, gibberellic
acid biosynthesis is stimulated in these tissues as the auxin is transported.
Second,
the auxin stimulates the release of sugars from the leaves. High levels of IAA-
ester
conjugates in phloem have been correlated with increased phloem loading of
sugars
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(Davies 1995). The sugar loaded into the phloem can then be transported into
developing fruits, tubers, or other sink tissues.
[075] Finally, and perhaps most importantly from a crop management
standpoint, this auxin moves into root tissues. Although some auxin in root
tissues is
beneficial, oversupply is harmful. Because roots normally have very low levels
of
auxin, root tissue is very sensitive to auxin levels. In fact it takes 100-
fold more IAA
to cause shoot sensitivity than it does to cause root sensitivity (Davies
1995). As a
result of the high sensitivity of roots to the auxin gradient, the transport
of large
quantities of IAA from fruiting bodies overloads these cells and inhibits root
cell
growth. This is evidenced by the observations that root decline coincides with
fruit
set in soybean, and soybean plants with higher pod numbers show faster
decline. An
overabundance of auxin can both inhibit cell division directly and increase
the
synthesis of ethylene and subsequently abscisic acid. This will ultimately
lead to root
senescence and plant death.
[076] The physical manifestations of this mass exodus of auxin into the roots
can be observed in many crops. In corn the number of adventitious roots, known
as
brace roots, will increase. In addition there will be an obvious downward turn
of root
growth and a decrease in meristematic root growth as evidenced by a lack of
fine
white roots. In legumes such as soybean and snap bean, this downward turn of
the
roots can also be observed, as can a decrease in meristematic roots and root
nodules. In potatoes, loss of meristematic root growth occurs, and other
stress
symptoms appear such as vine decline and sometimes verticillium wilt. This
early
root death can be altered by inhibition of this auxin flux into the roots,
either by
altering the IAA side of the gradient, or by adding cytokinin to counteract
the
increase. Prolonging root life will prolong the period in which fruiting
bodies fill and
mature.
[077] It is also important to note that these same conditions, i.e., an
increase
in auxin, abscisic acid, and ethylene, arise in roots when plants are under
stress
such as flooding, drought, and high salinity. Cytokinin application can reduce
these
stress hormone levels (Younis et al., 2003) and should therefore relieve the
stress.
The understanding that auxin production and transport actually becomes
inhibitory to
root growth is profound. Although it has been documented that auxin can be
applied
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to roots at levels high enough to arrest root growth, it has never been
suggested that
the plant synthesizes enough auxin to bring about its own death. It has also
been
observed that the supply of cytokinin can delay or even abolish senescence,
but it
has never been suggested that this is due to a balancing of auxin that would
otherwise lead to the production of factors that promote senescence in roots.
In our
ongoing experiments we are learning that cytokinin, when applied at or just
before
first flower, cannot only delay root decline, but can in fact increase
meristematic
roots to levels even higher than before flowering. This application will
increase plant
life and reduce plant stress, and has even been observed to alleviate symptoms
of
verticillium wilt infection in potato.
[078] Because conditions for plant growth are never ideal as defined here,
hormone levels are not always at optimum concentrations. By understanding how
hormone levels change in response to the environment and development of the
plant, we can learn how we can assist the plant to produce the results best
for our
particular situation. For example, if temperatures have been very high or very
low,
we understand that the plant will be unable to produce auxin, and we can
supplement it. Likewise we can alter the auxin and cytokinin gradients at
different
times of development to alter growth toward that which is most beneficial for
that
particular crop situation. When plants are very young, in the seedling or new
transplant stage, auxin should be applied to the roots. This will stimulate
early root
establishment and will be evident in plants that take hold faster and
initially produce
true leaves earlier than untreated plants. Low levels of auxin supplied to the
roots
throughout the vegetative stage will be beneficial in establishing and
maintaining
healthy roots, and will keep vineing down in sweet potato and irish potato.
[079] Most growers skilled in the art know the appropriate internode length
for their crop. If a grower wants to reduce the internode length of new shoot
growth,
an application of auxin to the roots will accomplish this. If internode length
should be
increased, an application of gibberellic acid to the shoots will deliver
results.
Likewise experienced growers know the appropriate amount of top growth for
their
crop. If top growth is too prolific, addition of auxin to the roots will slow
new shoot
development. If more top growth is desired, addition of cytokinin to the roots
will
stimulate more shoot growth and more branching. If a grower notices excessive
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flower abortion, a spray of auxin will help with retention. After plants have
made the
transition to flower, they oversupply auxin to the roots. Therefore cytokinin
should be
applied to the roots to balance this high level of auxin being transported
down from
flowers and fruits. In addition, if plants are under stress from heavy fruit
load,
flooding, drought, saline soils, or pathogen infection, ethylene and abscisic
acid build
up in the roots. Cytokinin should again be applied to correct this problem.
Addition
of cytokinin to the root area will balance the effects of excess auxin,
abscisic acid, or
ethylene and prolong root life.
[080] Through these applications it is possible to increase root size, extend
root life, decrease internode length, increase lateral branching, regulate the
appearance of new top growth and increase fruit quality. Through the methods
of
this invention, growers will gain an understanding of how crops grow and how
to
assist the crop plants to produce the maximum yield from their potential.
[081] The present invention is directed to methods for controlling the growth
of plant tissues by manipulating the levels and ratios of plant hormones in
the plant
tissue, particularly in the roots of the plants. By manipulating there hormone
levels
and ratios, growth of the plant can be controlled to increase root size,
extend root
life, alter internode length, increase lateral branching, regulate appearance
of new
top growth and increase fruit quality.
[082] In the methods of the present invention, a plant hormone, e.g., an
auxin, in an amount effective to produce the desired improved plant
architecture and
the resulting improvement in plant growth and productivity is applied to the
plant
tissue. While the auxin is applied in an amount sufficient to produce the
desired
result, it must be applied in an amount insufficient to negatively affect
growth of plant
tissue. Alternatively, the level, ratio or effectiveness of endogenous or
applied
hormone may be manipulated to fall within ranges to produce those results. The
desired manipulation can be achieved by applying other plant growth regulators
(PGRs), e.g., plant hormones such as the kinetins and gibberellins, more
specifically
cytokinin and gibberellic acid, and their precursors and/or derivatives in
effective
amounts.
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[083] The presently preferred plant hormones for use in the methods of the
present invention are the auxins. Auxins useful in the methods of the present
invention are selected from the group consisting of the natural auxins,
synthetic
auxins, auxin metabolites, auxin pre-cursors, auxin derivatives and mixtures
thereof.
The preferred auxin is indole-3-acetic acid (IAA), a natural auxin. The
preferred
synthetic auxin is indole-3-butyric acid (IBA). Other exemplary synthetic
auxins
which may be employed in the methods of the present invention include indole
propionic acid, indole-3-butyric acid, phenylacetic acid, naphthalene acetic
acid
(NAA), 2,4-dichlorophenoxy acetic acid, 4-chloroindole-3-acetic acid, 2,4,5-
trichlorophenoxy acetic acid, 2-methyl-4-chlorophenoxy acetic acid, 2,3,6-
trichlorobenzoic acid, 2,4,6-trichlorobenzoic acid, 4-amino-3,4,5-
trichloropicolinic
acid and mixtures thereof. Other plant growth hormones which act by altering
the
level or effectiveness of endogenous or applied auxin within the plant tissue
may
also be applied. These hormones (PGRs) may include ethylene, cytokinins,
gibberellins, abscisic acid, brassinosteroids, jasmonates, salicylic acids and
precursors and derivatives thereof.
[084] In one embodiment of the methods of the present invention, the plant
hormone, e.g., an auxin or another PGR, is applied to the seeds or tubers of
the
plant prior to planting. When applied to the seeds or tubers, e.g., to bean
seeds or
potato pieces, respectively, an auxin should be applied at a rate of about
0.0028 to
about 0.028 grams auxin per 100 kg seed weight. In a more preferred
embodiment,
the auxin is applied to seeds, e.g., bean seeds, at a rate of about 0.016 to
about
0.112 grams auxin per 100 kg seed weight. On the other hand, when applied to
potato seed pieces, the auxins should be applied at a rate to result in about
0.125 to
about 2.8 grams auxin per hectare of planted seed pieces. In a more preferred
embodiment, the rate of application to potato seed pieces should result in
about
0.125 to about 0.28 grams auxin per hectare of planted seed pieces. When
applied
to the roots, foliage, flowers or fruits of plants, the auxin should be
applied at a rate
of about 0.0002 to about 0.06 grams auxin per hectare per day, more preferably
at a
rate of about 0.002 to about 0.01 grams auxin per hectare per day. Application
may
be made over a series of days during the growing period based upon perceived
stress on the plants and observed infestation. Alternatively, another PGR may
be
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applied at a rate sufficient to manipulate the level of endogenous and/or
applied
auxin to within the stated ranges.
[085] In a more preferred embodiment of the methods of the present
invention, the hormone is applied to the roots, foliage, flowers or fruits of
a plant after
planting. While application to the roots or tubers prior to planting or by
soil
application after planting, may produce the best results in some
circumstances, in
others, application to the foliage may be preferred. The specific crop and the
desired
result must be taken into account when selecting an application method.
[086] The plant hormone, e.g., an auxin or another PGR, may be applied as
an aqueous solution or as a powder. When applied as an aqueous solution, the
solution may include a metal selected from the group consisting of the
alkaline earth
metals, the transition metals, boron and mixtures thereof. Preferred metals
include
calcium, magnesium, zinc, copper, manganese, boron, iron, cobalt, molybdenum
and mixtures thereof. Most preferred are calcium and boron. When included, the
metal may be present in a range from about 0.001 to about 10.0 percent-by-
weight,
preferably from about 0.001 to about 5.0 percent-by-weight. The preferred
method
of applying the PGRs may be along with a boron-containing solution, including
up to
about 10.0 percent-by-weight boron. Boron will tend to stabilize the auxins in
plant
tissues to which such solutions are applied.
[087] The application of a metal, preferably boron, together with the PGR
appears to extend the effective life of the PGR, thus permitting longer times
between
repeat applications. Boron appears to improve the efficacy, both the life and
activity,
of added IAA by suppressing the activity and or synthesis of IAA-oxidase, the
enzyme that degrades IAA in plants. The anti-oxidant ascorbic acid may be part
of
the mechanism through which boron enhances IAA activity. Boron also enhances
sugar transport in plants, cell wall synthesis, lignification, cell wall
structure through
its borate ester linkages, RNA metabolism, DNA synthesis, phenol metabolism,
membrane functions and IAA metabolism. Further, boron is known to modulate
respiration. The boron requirement for reproductive growth is higher than that
for
vegetative growth. Boron interacts with auxin especially in cell elongation
such as
pollen tubes, trichomes and other cells. Boron also stimulates auxin-sensitive
plasmalemma NADH-oxidase and is necessary for the auxin stimulation of
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ferricyanide-induced proton release in plant cells. Boron is also part of the
endocytosis mechanism of rhamnogalacturonan II dimers (linking through di-
ester
bonds) in formation of primary walls in dividing cells such as root tips,
trichomes or
pollen tubes. Thus, boron is linked with auxin-mediated cell division as well
as
auxin-mediated cell elongation. Finally, boron has been reported to have anti-
fungal
and anti-bacterial activities. Accordingly, it is believed that application of
PGRs,
together with boron, will improve the effect of the PGR in suppressing insect
and
pathogen infestation in plants.
[088] The active half-life of IAA and IBA is rather short. This is due to the
ability of the plant to metabolize these two auxins. IAA oxidase is the enzyme
that is
responsible for the catabolism of IAA. One of the functions of gibberellic
acid is to
increase IAA oxidase, so that gibberellic acid can control cell growth. On the
other
hand, boron decreases the level of IAA oxidase. One can readily see that an
adequate amount of boron will extend the half-life of IAA and/or IBA by
reducing IAA
oxidase, the enzyme that degrades these two hormones.
[089] If IAA and IBA are combined with a boron-containing material, it will
allow the auxins to exert more influence over cell growth, cell division, and
the
dominance of the cell by gibberellic acid. This is clearly shown by the use of
PGRs in
conjunction with a boron solution containing methyethylamine (MEA). When
applied
as a topical application to crops, internode length was reduced and both stem
diameter and root mass were increased. These growth characteristics clearly
show
that the dominant activity of gibberellic acid is reduced in the plant. This
is similar to
the way a plant grows at lower temperatures in the range of about 22 C.
[090] When applied as an aqueous solution, a solution containing the plant
hormone, e.g., an auxin or another PGR, may be sprayed on seeds or tubers
using
conventional spray equipment. Alternatively, the seeds or tubers may be
immersed
in an aqueous solution of the hormone.
[091] When applied to the roots, foliage, flowers or fruits of plants, an
aqueous solution containing the hormone, e.g., an auxin or another PGR, may be
applied using conventional irrigation or spray equipment. Alternatively, the
hormone
may be applied in a dry form as a powder. When so applied, the hormone is
mixed
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with a biologically and environmentally compatible material. Such a powder may
be
applied to the foliage, flowers or fruits by conventional dusting equipment.
[092] Alternatively, the powder may be encapsulated in a biologically
compatible material to provide for slow release when placed on or near the
seeds,
tubers or roots of the plant. Such encapsulated materials may be placed
directly on
the seeds or tubers or may be dispersed within the root zone of the plant
where the
slowly released auxin may be absorbed by the roots. Exemplary biologically
compatible materials useful in encapsulation include the clays, lignites,
resins,
silicones and mixtures thereof.
[093] While the methods of the present invention may be used with
substantially all plants, they are particularly useful when applied to crop
plants, e.g.,
dry beans, soy beans, onions, cucumbers, tomatoes, potatoes, corn, cotton and
the
like.
[094] Finally, the present invention includes seeds and seed pieces for
producing plants which have been treated in accord with the present invention.
Such
seed pieces include a plant seed or seed piece having dispersed on the surface
thereof a plant hormone, e.g., an auxin or another PGR, in an amount effective
to
inhibit growth of harmful organisms in or on tissues of the plant, but in an
amount
insufficient to negatively affect growth of the plant tissues. Alternatively,
such seeds
and seed pieces have dispersed on the surface thereof a PGR in an amount
sufficient to manipulate the endogenous and/or applied hormone level or ratio
to
within a range for producing the desired result. Such seed pieces may be
prepared
by spraying an aqueous solution of the hormone, e.g., an auxin or another PGR,
onto the surface of seeds or seed pieces. Alternatively, the seeds or seed
pieces
may be immersed in an aqueous solution of the hormone. In the presently
preferred
embodiment, the hormone is present in an amount of about 0.0028 to about 0.028
grams of auxin per 100 kg seed weight of beans and similar seeds. Where the
seed
piece is a potato seed piece, the auxin, in the presently preferred
embodiment, is
present in an amount to result in about 0.0125 to about 2.8 grams auxin per
hectare
of planted seed pieces.
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[095] Following are several examples of use of the methods of the present
invention to effect the growth of various plants. These examples are provided
by
way of illustration only and are not intended to limit the scope of the
invention in any
way.
[096] EXAMPLE 11
In this experiment, the effects of PGRs on radish growth were
observed. A total of eighty (80) plants were used for this experiment. Twenty
(20)
plants were treated with water as a control. Twenty (20) plants were treated
with a
PGR solution corresponding to a rate of 12 oz/acre. The PGR solution is an
aqueous solution including 0.015% IAA, 0.005% IBA, 0.009% cytokinin and 0.005%
gibberellic acid as active ingredients. Also present as inactive ingredients
are
1.000% emulsifier, 0.850% surfactant and 0.050% defoamer. A small measure,
0.0084 ml of this solution, was diluted into 100 ml of water and applied to
the soil of a
container having a surface area of about 1 square foot to correspond to an
application rate of 12 oz/acre. Twenty (20) plants were treated with an auxin
solution
containing indole-3-acetic acid (IAA) at a rate of 0.84 micrograms in 100 ml
water per
square foot of surface area of the container. Finally, twenty (20) plants were
treated
with the cytokinin kinetin at a rate of 0.84 micrograms in 100 ml water per
square
foot of surface area of the container. Treatments were applied to soil at the
time of
planting and repeated every week thereafter. Length of the hypocotyl and
largest
leaf of each plant was measured 21 days after planting. The mean hypocotyl
length
and leaf length was calculated. Results are tabulated in Table I and
illustrated in
Figs. 3 and 4.
[097] TABLE I
Effects of PGR on Radish Growth
Treatment Average Hypocotyl Average Leaf
Length (mm) Length (mm)
Control 44.70 3.50 91.75 3.99
PGR solution 54.10 3.42 109.65 t 4.87
Auxin 51.15 2.64 121.15 t 5.20
Cytokinin 46.10 3.10 101.25 4.46
Hypocotyl and leaf lengths are expressed in millimeters t standard deviation
of the
mean.
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[098] Treatments in accord with the present invention, whether using a single
hormone, e.g., an auxin or cytokinin, or a combination as provided by the PGR
solution result in production of leaves characterized by both increased
average leaf
length and average hypocotyl length.
[099] In this portion of the experiment radish plants were treated twice at
four
day intervals. Plants were treated first on emergence, and again four (4) days
later.
Measurements were taken one week after the last treatment. Treatments are
equivalent to 6 oz/acre, 12 oz/acre, and 24 oz/acre of PGR solution, while the
IAA
and kinetin treatments are equivalent to the relative amounts in the 6 oz/acre
rate of
PGR solution. The second treatment was applied two inches to the left of the
seedlings and, therefore, did not contact the seedling roots. The results of
these
experiments are tabulated in Table II and illustrated in Fig. 5.
[0100] TABLE II
Radish Height Data
Treatment Shoot Height (mm)
Foliar Applied
Control 107.89 t 4.65
6 oz PGR solution 96.23 t 4.62
12 oz PGR solution 79.04 t 4.22
24 oz PGR solution 64.77 t 4.02
Auxin 91.46 t 4.20
Cytokinin 89.00 t 4.55
Auxin + Cytokinin 68.36 3.97
Shoot height is expressed in millimeters standard deviation of the mean.
Sample
size is 15 plants.
[0101] EXAMPLE 2
In this experiment, the effects of PGRs on tomato yield were
determined. Tomato variety TSH04, which is a processing tomato, was used. All
plants were grown in five gallon pots in a greenhouse. Eight plants were used
for
each treatment. Application of the treatments was done aerially to eight
plants and
in the soil for eight plants to allow comparison of soil versus foliar
application of the
PGRs. Treatments were 6 oz/acre PGR solution. The treating solutions were
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prepared by diluting 0.0042 ml of concentrated solution into 100 ml water for
application to the soil, or into 50 ml water for foliar application. The IAA
solution was
prepared by diluting 0.42 micrograms of IAA into 100 ml water for application
to the
soil, or into 50 ml water for foliar application. The cytokinin solution was
prepared by
diluting 0.42 micrograms of kinetin into 100 ml water for application to the
soil, or into
50 ml water for spraying of the foliage. The solution containing both IAA and
kinetin
at a 1:1 ratio was prepared by diluting 0.42 micrograms of IAA and 0.42
micrograms
of kinetin into 100 ml water for application to the soil, or into 50 ml water
for foliar
application. A solution containing both IAA and kinetin at a 4:1 ratio was
prepared by
diluting 0.42 micrograms of IAA and 0.11 micrograms of kinetin into 100 ml
water for
soil application, or into 50 ml water for foliar application. Finally, a
solution
containing both IAA and kinetin at a 1:4 ratio was prepared by diluting 0.11
micrograms of IAA and 0.42 micrograms of kinetin into 100 ml water for soil
application, or into 50 ml water for foliar application. Water was employed as
a
control. Plants were kept pruned to one fruiting truss per plant and the
weight of the
fruit from each plant was measured when most of the fruit had ripened (112
days
after planting). Results are tabulated in Table Ill. Figs. 6 and 7 illustrate
the
increased fruit weight achieved, respectively, for total and individual fruits
with each
treatment.
[0102] TABLE Ill
Effects of PGRs on Total Fruit Weight
Treatment Average total fruit weight Average weight of each
per plant (grams) fruit (grams)
Water 56.79 4.28 12.36 2.90
Water + NitroPlus9 93.19 5.49 10.13 1.84
Auxin 63.79 7.59 11.45 1.99
Cytokinin 89.08 6.85 14.76 2.47
Auxin + Cytokinin 1: 1 107.41 6.99 18.34 3.12
Auxin + Cokinin 4:1 75.90 8.24 16.38 3.16
Auxin + Cytokinin 1:4 52.19 5.23 11.73 2.92
PGR solution 48.83 5.49 12.75 3.29
Fruit weight is expressed in grams standard deviation of the mean.
NitroPlus9 is a solution containing, as active ingredients, amines complexed
with
calcium or magnesium chloride. NitroPlus9 is a trademark of Stoller
Enterprises, Inc.
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[0103] Tomato plants treated in accord with the present invention appear to
generally produce more and heavier fruit, particularly where the treating
solution
includes both and auxin and cytokinin in equal parts.
[0104] EXAMPLE 3
In this experiment, the effect of PGRs on cucumber internode length
was determined. The cucumber variety used was the National pickling cucumber
distributed by NK Lawn & Garden Co. (Chattanooga, TN). Eight plants were used
per treatment. Treatments were applied to the soil of each five-gallon pot
containing one plant per pot. Treatments were 6 oz/acre PGR solution. The
final
PGR solution was prepared by diluting 0.0042 ml of the concentrated solution
into
100 ml water. The IAA solution was prepared by diluting 0.42 micrograms of IAA
into 100 ml water. The cytokinin solution was prepared by diluting 0.42
micrograms
of kinetin into 100 ml water. Finally, plants were treated with 6 oz/acre N-
Large.
The treating solution was prepared by diluting 0.0042 ml of the commercial
solution
into 100 ml water. N-Large is a formulation containing 4 percent gibberellin
(GA3).
Water was used as a control. Treatments were applied to the soil at the time
of
planting, and weekly thereafter. Twenty-one (21) days after planting, the
internode
length of the first (bottom), second (middle), and third (top) internodes were
measured to the nearest millimeter. The average internode length for first,
second,
and third internodes was calculated for each treatment. Results are tabulated
in
Table IV and illustrated in Fig. 8.
[0105] TABLE IV
Effects of PGRs on Cucumber Internode Length
Treatment Internode 1 Internode 2 Internode 3
Control 122.00 4.13 35.00 4.36 8.25 2.50
PGR solution 109.63 4.11 38.00 4.21 9.25 2.97
Auxin 115.88 4.01 25.38 3.13 4.50 1.91
Cytokinin 106.38 3.98 20.25 3.40 2.13 1.25
Gibberellic Acid 124.38 3.80 31.00 3.68 4.63 2.13
Internode length is measured in millimeters standard deviation of the mean.
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[0106] Cucumbers were harvested and weighted to the nearest gram eighty-
four (84) days after planting. At the same time, the total vine length was
measured
to the nearest millimeter. In addition, the number of internodes and number of
branches were also counted. Average vine length, average internode number,
average branch number, average internode length and average cucumber weight
were determined. Results are tabulated in Table V and illustrated in Figs. 9a-
9e.
[0107] TABLE V
Effects of PGRs on Cucumber Vines and Fruit
Treatment Average Average Average Average Average
Vine Length Internode Branch Internode Cucumber
(mm) Number Number Length Weight (gm)
(mm)
Control 301.0 7.14 31.00 2.38 2.6 1.3 9.74 0.57 294.91 7.75
PGR Solution 289.75 5.55 33.00 1.57 4.75 1.58 8.79 0.88 352.06 6.87
Gibberellic 252.38 4.56 27.63 1.46 5.13 1.55 9.14 0.62 242.66 9.67
Acid
Kinetin 255.50 5.61 30.50 1.75 6.25 2.27 8.37 0.62 229.71 1.33
IAA 267.00 5.70 30.75 1.96 7.25 1.86 8.72 0.87 311.98 9.17
Vine length and internode length were measured to the nearest millimeter.
Internode
length was calculated by dividing the vine length by the internode number.
Cucumber weight was measured to the nearest gram. All measurements are shown
the standard deviation of the mean.
[0108] EXAMPLE 4
In this experiment, the effects of PGRs on the growth of bell pepper
plants were evaluated. Each of four (4) pepper plant replicates were grown
outdoors
in a field. The plants were grown with a spacing of 12 inches between plants
and 42
inches between the rows of plants. Each replicate had fifty (50) plants for
each
treatment. Five (5) plots of plants were treated once after transplanting with
PGR
solutions applied at the rates of 3, 6, 12, 18 or 24 oz per acre. A final plot
was
treated with seven (7) applications of the PGR solution applied bi-weekly
beginning
after transplanting. The PGR solution had a formulation including 0.015% IAA,
0.005% IBA, 0.009% cytokinin and 0.005% gibberellic acid as the active
ingredients.
Also present in the solution were 1.000% emulsifier, 0.850% surfactant and
0.050%
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defoamer. The solutions were applied to the plants from drip lines in two (2)
gallons
of water per treatment plot for each of the treatments in each of the
replicates.
Measurements of plant height, canopy diameter and root weight were taken
ninety-
seven (97) days after transplanting. Plant height in centimeters was measured.
Canopy diameter at its widest was measured in centimeters. The weight of the
roots
in grams was measured after shaking off the soil. The results are reported in
Table
VI. The effect on plant height, canopy diameter and root weight are
illustrated in
Figs. 10a -10c, respectively.
[0109] TABLE VI
Effects of PGRs on Pepper Crop Plant Growth
Treatment Rate Application Average Average Average
(oz/acre) Frequency Height Canopy Weight
(cm) Diameter (gm)
(cm)
Control 0 0 29.5 d 13.6 d 13.4 e
PGR 3 1 30.0 d 16.0 c 13.1 de
PGR 6 1 33.2c 17.6bc 21.7b
PGR 12 1 34.3 be 18.0 abc 17.0 cd
PGR 18 1 33.7 c 18.1 ab 17.7 c
PGR 24 1 36.7a 19.Oab 17.5c
PGR 12 Biweekly 36.3 ab 20.0 a 27.7 a
Means are different at 5% probability when followed by a different letter.
[0110] Application of PGR solutions resulted in increased plant height, canopy
diameter and root weight. Plant height and canopy diameter both increased at
successively higher rates of application. Plant bushiness was greatest for the
PGR
treated plants; height was also greater. Root weight was significantly
increased with
repeated application of the PGR solution. Most PGR treatments had better root
growth than the control plants.
[0111] EXAMPLE 5
In this experiment, the effects of PGRs on the size and weight of bell
peppers were evaluated. Each of four (4) pepper plant replicates were grown
outdoors in a field. The plants were grown with a spacing of 12 inches between
plants and 42 inches between the rows of plants. Each replicate had fifty (50)
plants
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for each treatment. Five (5) plots of plants were treated once after
transplanting with
PGR solutions applied at the rates of 3, 6, 12, 18 or 24 oz per acre. A final
plot was
treated with seven (7) applications of the PGR solution applied bi-weekly
beginning
after transplanting. The PGR solution had a formulation including 0.015% IAA,
0.005% IBA, 0.009% cytokinin and 0.005% gibberellic acid as the active
ingredients.
Also present in the solution were 1.000% emulsifier, 0.850% surfactant and
0.050%
defoamer. The solutions were applied to the plants from drip lines in two (2)
gallons
of water per treatment plot for each of the treatments in each of the
replicates.
Peppers were harvested from all the plants in all of the plots. The number of
peppers per plant was recorded. The weights of the harvested peppers were
determined. The percentage of large peppers (those graded fancy - first grade)
was
calculated. The results are recorded in Table VIII. The yield per plant and
percentage of large peppers are illustrated in Figs. 11 a and 11 b.
[0112] TABLE VII
Effects of PGRs on Pepper Crop Harvest
Treatment Rate Application Average Average Large
(oz/acre) Frequency Peppers per Yield (gm) Peppers
Plant %
Control 0 0 3.1 a 283 b 19 b
PGR 3 1 2.8 a 288 b 42 ab
PGR 6 1 2.7 a 303 b 32 b
PGR 12 1 3.3a 418ab 38b
PGR 18 1 2.7 a 308 b 37 b
PGR 24 1 2.9 a 352 b 37 b
PGR 12 Biweekly 3.6 a 563 a 62 a
Means are different at 5% probability when followed by a different letter.
[0113] Though the application of PGR solutions to the pepper plants did not
appear to significantly change the number of peppers harvested, it had a
marked
effect on the size and yield of the peppers. The percentage of peppers
classified as
large, i.e., fancy - first grade, significantly increased, resulting in a
significant
increase in the average yield per plant. The largest peppers and the greatest
yield
were obtained with biweekly application of the PGR solution.
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[0114] EXAMPLE 6
In this experiment, the effects of PGRs on corn stalk growth were
evaluated. Each of four (4) corn plant replicates were grown outdoors in a
field. The
rows of plants were separated by 42 inches. The plant density was about 30,000
per
acre. The plants were treated with 8, 16 or 24 oz/acre of a PGR solution once
after
seeding of the corn. The PGR solution had the same composition as that used in
Example 4. The solutions were applied to the corn from drip lines in 2 gallons
of
water per treatment plot for each of the treatments in each of the four (4)
replicates.
The circumference of the stems of ten (10) plants from each treatment in each
of the
four (4) replications were measured forty-eight (48) days after planting. The
results
are reported in Table VIII.
[0115] TABLE VIII
Effects of PGRs on Field Corn Stalk Circumference
Treatment Rate Application Average Stalk Circumference (mm)
(oz/acre) Frequency
Control 0 0 75.3 3.0
PGR 8 1 79.9 2.1
PGR 16 1 79.4 0.8
PGR 24 1 77.3 3.2
Means are different at 5% probability when followed by a different letter.
[0116] Corn stem circumference increased with increasing concentration of
the applied PGR solution. A maximum response was reached at the 16 oz/acre
rate
and then decreased slightly at higher rate.
[0117] EXAMPLE 7
The effects of PGRs on the growth and yield of bell pepper plants were
evaluated in this experiment. The experiment employed a randomized (4)
replicate
trial. The bell peppers were planted 12 inches apart in 2 rows with 40 inches
between rows. The PGR solution had the same composition as that used in
Example 4. Controls were merely treated with water. The solutions were applied
to
the plants at the rate of 6 or 12 oz per acre from drip lines. The PGR
solutions were
applied shortly after transplanting as a single treatment or on a repeated bi-
weekly
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basis as indicated in Table IX. The plant height and canopy width were
measured at
maturity. Peppers were harvested from all of the plants in all of the plots.
The
weights of the harvested peppers were determined. The percentage of larger
peppers (those graded fancy - first grade) was calculated. The weight of the
plant
roots were determined after harvest. The results are reported in Table IX
[0118] TABLE IX
Bell Pepper Crop Performance with PGR
Plant Canopy Root Fruit Wgt Fancy
Treatment Height Width (cm) Weight (g) Ave. (g) (%)
(cm)
Control 30 d 13.6 d 13.4 e 283 b 37 c
PGR (once 33 c 17.6 be 21.7 b 303 b 52 be
6 oz/acre
PGR (once 34 be 18 abc 17.0 cd 418 ab 62 ab
12 oz/acre
PGR (bi-weekly - 36 ab 20 a 27.7 a 563 a 77 a
12 oz/acre
Means followed by a different letter are different at p=0.05 (LSD).
[0119] Treatment with PGR results in larger plants with significantly larger
root
growth. Both the average weight of the harvested peppers and the percentage of
peppers graded fancy are dramatically increased, doubling with bi-weekly
application
in comparison to the control.
[0120] EXAMPLE 8
The effect of PGRs on onion yield was examined in this experiment.
This experiment employed a randomized (4) replicate trial. Onions were sown in
rows in 50 foot plots. The rows were 40 inches apart. Normal production
practices
were used in the trial. The PGR solution had the same composition as that used
in
Example 4. Controls were merely treated with water. The PGR solutions were
applied at the rate of 6 or 12 oz per acre from drip lines on a weekly basis
throughout
the growing season.
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[0121] TABLE X
Onion Crop Performance with PGR
Treatment Rate Large Onions Total Onions
(oz/acre (Bags per acre) (Bags per acre)
Control 0 370 551
PGR 6 499 635
PGR 12 698 819
[0122] Both the total yield and the yield of larger onions were significantly
increased by the application of PGR solutions on a weekly basis. As expected,
both
yields showed the greatest improvement when applied at the higher rate of 12
oz per
acre.
[0123] EXAMPLE 9
The effect of PGRs on the yield and grade of potatoes was evaluated
in this experiment. Potatoes were planted in 40 foot rows with a spacing of 36
inches between rows. Treatments were replicated 5 times. Normal production
practices were followed. The PGR solution used in this experiment comprised an
aqueous solution containing 0.015 % IAA, 0.005 % IBA, 0.009 % cytokinin, 0.005
%
gibberellic acid, 1.000 % emulsifier, 0.850 % surfactant and 0.050 % defoamer,
together with 8.0 % boron and 0.004 % molybdenum. The PGR solutions were
applied at the rate of 0.5 or 1.0 gallon per acre as a side dressing at the
last
cultivation between the rows. The potatoes were harvested, weighed and graded.
The results, including both total yield (lbs per plant) and yield of USA grade
No. 1
potatoes per plant, are reported in Table XI.
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[0124] TABLE XI
Effect of PGR/B/Mo on Potato Crop Performance
Treatment Yield Difference USA No. 1 potatoes Difference %
Ib/ lant % from Control Number per Plant from Control
Control 11.0 0.4 10.4
PGR/B/Mo 11.5 0.6 4.6% 11.2 t 1.4 7.7%
.7/o
0.5 gal/acre
PGR/B/Mo 14.1 0 28.3 % 14.4 4.1 38.5 %
1 gal/acre
Means are represented with their standard deviations.
[0125] Treatment with PGR/B/Mo solutions resulted in both improved total
yield and yield of grade No. 1 potatoes. At the higher application rate, the
total yield
is increased by more than 28 %, while the yield of grade No. 1 potatoes is
improved
by more than 38 %.
[0126] EXAMPLE 10
The effect of PGRs added together with conventional plant nutrients
on the yield and grade of potatoes was evaluated in this experiment. Potatoes
were planted in 40 foot rows with a spacing of 36 inches between rows.
Treatments were replicated 5 times. Normal production practices were followed.
The PGR solution used in this experiment comprised an aqueous solution
containing 0.015 % IAA, 0.005 % IBA, 0.009 % kinetin, 0.005 % gibberellic
acid,
1.000 % emulsifier, 0.850 % surfactant and 0.050 % defoamer, together with a
compliment of nutrients. The treatments were applied at the rate of one gallon
per
acre via side dressing at the last cultivation between the rows. The
treatments
were applied either on a weekly or bi-weekly basis as indicated in Table XII.
The
potatoes were harvested, weighed and graded. The results, including both total
yield (lbs per plant) and yield of USA grade No. 1 potatoes per plant, are
reported in
Table XII.
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[0127] TABLE XIl
Effect of PGR/Nutrient on potato crop performance
Difference
Treatment Yield % from USA No. 1 potatoes Difference %
(lb/plant) Control Number per Plant from Control
Control 11.0 0.4 10.4
PGR/Nutrient 12.8:t 0.6 16.4% 16.4 4.1 61.5%
(weekly)
PGR/Nutrient 15.6+1.8 42.0% 14.6 1.8 40.4%
(bi-weekly)
Means are represented with their standard deviations.
[0128] Treatment with both PGRs and nutrients produced both improved total
yield and yield of grade No. 1 potatoes. Total yield significantly increased
both bi-
weekly application, while the yield of grade No. 1 potatoes significantly
increased
with either application.
[0129] The foregoing description of the invention has been directed in primary
part to particularly preferred embodiments for purposes of explanation and
illustration. It
will be apparent, however, to those skilled in the art that many modifications
and
changes in the specifically described methods and compositions may be made and
the
scope of the claims should not be limited by the preferred embodiments set
forth. The
claims should be given the broadest interpretation consistent with the
description as a
whole. For example, while indole-3-acetic acid is the preferred auxin,
synthetic auxins,
specifically, indole-3-butyric acid, may be employed. Further, other plant
growth
regulators, particularly cytokinins or gibberellins, may be used to manipulate
the auxin
levels. Further, while preferred application rates have been presented, it is
known that
different plant species and, in fact, different tissues within a given plant
all require
different auxin levels. Thus, those skilled in the art may readily adjust the
suggested
application rates as required to achieve the desired results. Further, while
Applicant has
attempted to explain the reasons for the observed improvements in plant
architecture,
growth and crop yield, Applicant does not wish to be held to the theory
proposed,
because that mechanism is not fully understood.
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