Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF THE INVENTION
Method of Producing F1 Hybrid Seeds
BACKGROUND OF THE INVENTION
The present invention relates to a method of producing
F, hybrid seeds for plants which show a
heteromorphic self-incompatibility.
For a long time, an agricultural technique
called F1 hybrid, which is generally for use in
treating allogamous plants, has been proved to be
quite effective in plant breeding. Particularly,
this technique has been proved to be extremely
useful for obtaining elite varieties for
allogamous crops such as corn and rape seed. For
this reason, it has long been demanded to establish a
practically useful technique for effectively obtaining
F1 hybrid seeds . To establish such technique, what has
been most generally used is cytoplasmic male sterility
line. But, a problem with such technique is that it is
often difficult to find cytoplasms that induce male
sterility in many kinds of plants . In order to solve this
problem, there has been suggested a method of
producing F1 hybrid seeds by making use of an
incompatibility. This method has been practically used
in a process of plant breeding, particularly for
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producing improved varieties for several sorts of
vegetables belonging to Brassica species, such as
cabbage which shows homomorphic self-
incompatibility.
Onthe otherhand, itis allowed to consider using
a method of producing F1 hybrid seeds for plants which
show a heteromorphic self-incompatibility. However,
at present, there is still not any practically usable
method which can be employed to obtain F1 hybrid seeds
in a large amount suitable for an industrial purpose.
One of the reasons for this situation is that there
is still not a industrially useful method for
producing a line consisting only of long-styled
flower plants or short-styled flower plants.
According to research in the field of
fertilization physiology, it is known that a small amount
of hybrid seeds are obtainable in an experiment where
a mating process is conducted among long-styledflower
plants by way of manual operation, but such
mating process is not suitable for breeding a line
consisting only of long-styled flower plants which is
ready for industrial seed production. At present, as
a practically usable method for obtaining F1 hybrid
seeds at an experiment level, a mating process is
conducted among different lines through manual
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operation. Alternatively, long-styled flower plants
or short-styled flower plants are moved from a group
consisting of one line, and then subjected to
pollination of pollens from other lines by way
of pollinators. However, the above methods have been
proved to be too high in cost because they need a lot of
labours in the production of a large amount of F, hybrid
seeds, thus they are not suitable for an industrial
purpose.
SUMMARY OF THE INVENTION
It is an obj ect of the present invention to provide
an improved method of producing F1 hybrid seeds for plants
which show a heteromorphic self-incompatibility, so as
to solve the above-mentioned problems peculiar to the
above-mentioned prior arts.
According to the present invention, there is
provided a method of producing F1 hybrid seeds for
plants showing a heteromorphic self-incompatibility,
said method comprising the steps of : selecting long-styled
flower plants from a group of plants showing a
heteromorphic self-incompatibility; placing the
selected long-styled flower plants in an
isolated condition; conducting an artificial
pollination or natural hybridization to effect a
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predetermined hybridization so as to breed a line
consisting only of long-styledflower plants; conducting
artificially or naturally a further hybridization
within the above line under a condition where this line
is isolated from other lines; proliferating seeds
so as to produce a seed parent line consisting only
of long-styled flower plants; planting a seed parent line
(line A) consisting only of long-styled flower plants;
planting, in the vicinity of line A, another line (line
B) consisting only of short-styled flower plants or
consisting of both the short-styled flower plants and
long-styled flower plants; harvesting seeds of line A
fertilized by pollen of line B, thereby producing F1 hybrid
seeds through hybridization between line A and line B.
In one aspect of the present invention, the
plants showing a heteromorphic self-incompatibility
include several cultivars of buckwheat. In detail,
the several cultivars of buckwheat include
Kitawasesoba, Kitayuki, Botansoba, Shinanonatsusoba,
Shatilovskaya 5, Ballada, Sumchanka.
The above objects and features of the present
invention will become better understood from the
following description with reference to the accompanying
Tables.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The methods according to the present invention may
be described in detail in the following.
Brief Description of the Present Inven ion
At first, long-styled flower plants are selected
from a group of plants showing a heteromorphic
self-incompatibility and are placed in an isolated
condition. Then, artificial pollination or natural
hybridization is conducted to effect a desired
hybridization so as to breed a line consisting only of
long-styled flower plants. Further, under a
condition where this line is isolated from other
lines, a further hybridization is conducted
artificially or under a natural condition, thereby
proliferating seeds so as to produce a seed parent line
consisting only of long-styled flower plants.
Further, according to the present invention, a
seed parent line (line A) consisting only of long
styled flower plants are planted. Then, in the
vicinity of line A, are planted another line (line
B) consisting only of short-styled flower plants or
consisting of both the short-styled flower plants and
long-styled flower plants. Finally, seeds of line A
fertilized by pollen of line B are harvested,
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thereby producing F1 hybrid seeds through hybridization
between line A and line B.
Experiments Embodvinc~ the Present Invention
At first, short-styled flower plants were removed
from a group of Kitawasesoba plants (a cultivar of
buckwheat showing a heteromorphic self-
incompatibility), so that only long-styled flower
plants were left. Then, the long-styled flower
plants were covered with a cage so that they were
completely isolated from the surrounding
environment. Afterwards, some pollinators were
introduced into the same cage. In this way, a
desired hybridization happened, and seeds were
produced to an extent which was 1/4 of an amount
obtainable under a common cultivation condition. Then,
the produced seeds were harvested and sowed, and it was
found that next generation were all long-styled flower
plants. Further, under a natural condition, the above
plants were placed on a field away from other buckwheat
lines, and it was found that a predetermined hybridization
happened and seeds were produced, thereby producing a
seed parent line consisting only of long-styled flower
plants . It is understood from the above process that it
is possible to breed a line consisting only of long-
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styled flower plants in a large scale suitable for
industrial purpose.
After some similar experiments were conducted on
other six kinds of buckwheat produced at home and abroad,
it was also found possible to produce seeds by
hybridization among only long-styled flower plants,
thereby producing seed parent lines consisting only of
long-styled flower plants.
Further, a group of Kitawasesoba individuals
consisting only of long-styled flower plants were
planted at different distances from a group of
Kitawasesoba individuals containing both the short
styled flower plants and long-styled flower plants.
It was found that a seed formation rate would
decrease if there was an increase in a distance between
any one individual of the former group (group of
Kitawasesoba individuals consisting only of long-
styled flower plants) and the later group (a group
of Kitawasesoba individuals containing short-styled
flower plants or containing both the short-styled
flower plants and long-styled flower plants).
Namely, the farther away a former group is from the
later group, the lower a seed formation rate will be. But,
it was proved that seeds were produced on all the test
individuals.
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When an investigation was made into the style of a
next generation, it was found that long-styled flower
plants and the short-styled flower plants were appearing
with a ratio of 1:1. It is clearly understood
from this fact that pollination from short-styled
flower is possible, and that almost all the groups
each consisting only of long-styledflower plants may
be fertilized by pollens from short-styled flower
plants.
As understood from the above description, with the
use of the present invention, if a line (line A) consisting
only of long-styled flower plants is bred and another
line (line B) containing short-styled flower plants is
cultivated in the vicinity of the line A, it is possible
to produce a large amount of F1 hybrid seeds at an
industrial level.
Heteromorph;c Self-incompatib;lit~
A self-incompatibility means a phenomenon where
although two plants have normal male and female sexual
organs and self-pollination is conducted, no
fertilization is effected. Heteromorphic self
incompatibility meansa phenomenon in which althoughthere
are existing long-styled flower plants (having long
styles and short filaments) and short-styled
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flower plants (having short styles and long filaments),
no seeds are produced during a mating process between two
plants having the same type flowers.
In fact, long-styled flower plants are homozygotes
with recessive gene "s", while short-styled flower
plants are heterozygotes with recessive gene "s" and
dominant gene "S". During a hybridization process
between such long-styled flower plants and short-styled
flower plants, ss and Ss will appear in a ratio of 1:1.
Usually, long-styled flower plants and short-styled
flower plants are maintained at a ratio of 1:1. But,
if a hybridization process is conducted among a group
consisting only of long-styled flower plants, next and
coming generations will all become long-styled flower
plants .
1 hybrid
When a mating process is conducted between two
differentself-fertilizationlines (orinbreeding lines),
it is allowed to obtain hybrid seeds during such
mating process. The obtained hybrid seeds may then be
bred so as to produce hybrid plants which are called
hereby F1 hybrid. Recently, for cross-fertilization
crops such as corn or some other vegetables,
some elite varieties of F1 hybrid have also been bred.
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Experiments
Three experiments were conducted in a manner which
will be described in detail below, with the use of
flowering plants.
Plant . Buckwheat (Fagopyrum esculentum Moench)
Varieties: Kitawasesoba, Kitayuki, Botansoba,
Shinanonatsusoba, Shatilovskaya 5, Ballada,
Sumchanka, Hokkai No.3
Pollinator: Stinging fly
Experiment 1
Operation
long-styledflower plants of Kitawasesoba (a kind
15 of buckwheat) just after their flowering were covered with
a cage so that insects may be prevented from flying
thereinto. Then, blossomedflowers were removed and 100
stinging flies were introduced into the cage. 90
days later, maturing plantindividuals were harvested,
20 the number of racemes and the number of seeds
produced were counted. The harvested seeds were then
sowed in a green house or on a field, and their styles
were observed. Meanwhile, a natural pollination was
conducted under a natural condition. Then, after
arriving at their complete maturation, 20 plants are
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randomly selected, the number of racemes and the number
of seeds produced were counted.
Results
In this experiment it was able to obtain desired seeds
by forcefully conducting a mating process among a
group of buckwheat individuals consisting only of
long-styled flower plants, as shown in Table 1. It was
found that although an amount of seeds produced in the
present experiment is greatly different from one
individual to another, seeds were produced from almost
all the buckwheat individuals.
Further, it was found that after the above seeds
was sowed in a green house and on a field which is
sufficiently separated from other buckwheat fields, the
desired seeds were obtained through an hybridization
among buckwheat individuals consisting only of
long-styled flower plants (the plants investigated
were all long-styled flower plants), as shown in Table
2.
As indicated in Table 2, when the plants derived from
the seeds of the plants grown in Cage 1 and Cage
2 were cultivated under a natural condition, it
was found that desired seeds were produced. Referring
again to Table 2, although the numberof yielded seeds
with respect to each raceme was only 1/2 of that
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obtainable under a condition when long-styled flower
plants and short-styledflower plants are cultivated in
a mixed manner, it is allowed to consider that
sufficient seed growth and sufficient line
maintenance had already been achieved. In this way,
it is sure to establish a practically useful method for
producing and maintaining a line consisting only of
long-styled flower plants.
The above desired seeds obtained in the
present experiment are intended to serve as a seed
parent line consisting only of long-styled flower
plants.
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Experiment 2
Qperation
With the use of a method which is the same as that
used in Experiment l, a mating process is conducted within
each of six groups consistinct of six kinds of
buckwheat (Kitayuki, Botansoba, Shinanonatsusoba,
Shatilovskaya 5, Ballada, Sumchanka), with the use of
six cages. These six kinds of buckwheat are those
produced at home and abroad, and consist only of
long-styled flower plants. After arriving at their
complete maturation, 20 plant individuals are
randomly selected from each group, the number of flowers
and the number of seeds produced were counted.
Results
Similar to Experiment 1, although an amount of
seedsproducedinthe present experiment is different
from one individual to another, the plants of the six
kinds were all able to produce seeds during the above
mating process, as shown in Table 3. As can be
understood from Table 3, it is possible to produce plant
lines consisting only of long-styled flower plants
regardless of a genotype.
CA 02264971 1999-03-08
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Experiment 3
A group of Kitawasesoba plant individuals involving
only long-styled flower plants are planted on different
positions which are separated 0 - 12 m from a pollen source
of a common Kitawasesoba containing long-styled flower
plants and short-styled flower plants. Further,
another kind of buckwheat plants (Hokkai No.3) were
planted among the above plants. Then, a mating
process was conducted under a natural condition.
Upon maturation, 20 plant individuals were
randomly selected, the number of racemes and the
number of seeds produced were counted. Further,
100 seeds were randomly selected from the above seeds,
sowed in a green house and cultivated there, and their
styles were investigated.
Results
Since it is well known that hybrid seeds will not
be produced through hybridization between
Kitawasesoba plants and Hokkai No.3 plants, because the
formeris a diploid and the latter is a tetraploid.
Thus, the seeds on the investigated plants were
produced either through pollination due to pollen from
pollen source of a common Kitawasesoba, or by
hybridization among only long-styled flower plants
1'7
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within the same test area. As shown in Table 4, the
farther away a test area is from a pollen source, the more
difficult will it be for a pollination (by the pollen
source) to occur. As a result, a longer distance
between a test area and a pollen source will result in
a lower efficiency of seed formation in the test area.
Further, it was found that the plants of the
next generation grown from the above seeds obtained in
the above test areas had involved long-styled flower
plants and short-styled flower plants in a ratio of 1: 1.
This means a fact that almost all the seeds obtained
in the present experiment in the above test areas were
fertilized by pollens of short-styled flower plants.
As is understood from this experiment, if a
group consists only of long-styled flower plants, and if
there is a possibility for the group of plants to accept
a pollination from short-styled flower plants, a
fertilization by the pollen from short-styled flower
plants will be prior to a fertilization by the
pollen from long-styled flower plants. Namely, if,
in the vicinity of a line A consisting only of
long-styled flower plants, there is planted a
line B containing short-styled flower plants, almost
all the plants of line A (or 100 0 of the plants of line
A) will be fertilized by pollen from line B, thereby
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obtaining F, hybrid seeds with a high efficiency.
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As is understood from the above description, with the
use of the above-described method of producing F_ hybrid
seeds, it is possible to produce F, hybrid seeds at an
industrial level, allowing people to develop new plant
varieties adapted to be produced with a high
productivity and having a uniform quality.
While the presently preferred embodiments of the
this invention have been shown and described above, it
is to be understood that these disclosures are for
the purpose of explanation and that various changes and
modifications may be made without departing from the
scope of the invention as set forth in the appended
claims.
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