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Practice English Speaking&Listening with: Asexual Plant Propagation

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Propagating plants is an inexpensive and easy way to get new plants from plants you already

have.

The two major methods of plant propagation are sexual and asexual propagation.

Sexual propagation is the reproduction of plants via seeds.

Asexual propagation is the reproduction of new plants from the stems, leaves, or roots

taken from the parent plant.

One of the most important benefits of asexual propagation is that plants produced by this

method are genetically identical to the parent.

A plant that is grown from a piece of another plant and is genetically identical to the

parent plant is known as a clone.

Trees and woody perennials are typically propagated by means of asexual propagation to preserve

the genotype clonally and reduce breeding time.

Im Dr. DeBusk and in this video, Ill focus on asexual plant propagation.

Asexual propagation has a number of advantages and disadvantages; therefore, when deciding

on the most efficient propagation technique to use, you should look at both the pros and

cons.

The number one advantage is that plants produced are genetically identical to the parent plant,

which means heterozygous material can be propagated without any genetic modifications.

Other advantages associated with asexual propagation are that plants are established more quickly,

they are more uniform, it is sometimes the only means of propagation (for example, seedless

fruits such as grapes), and seedborne diseases are not a problem.

The number one disadvantage is that typically producing plants vegetatively is more expensive

than using seeds.

A second problem occurs when plant material becomes infected with a virus that spreads

systemically throughout the plant and can thus be transmitted to other plants.

Viral infections can be minimized or eliminated by starting with disease-free seedlings and

maintaining virus-free stock plants for asexual propagation.

Other disadvantages associated with asexual propagation are difficulty with storage, handling,

and transport of asexual materials, which are much more cumbersome to handle than seeds.

A variety of types of asexual propagation can be used: Apomixis is a form of asexual

propagation in which seeds are produced without fertilization; for example, there is no fusion

of the male and female gametes, so these seeds are solely maternal in origin.

An excellent example of this type of asexual propagation is the common dandelion, found

in most lawns; it is capable of reproducing by seeds, vegetatively, or by apomixis.

Cuttings, the most common type of asexual propagation, refer to using a detached vegetative

part to produce a new plant.

The four types of cuttings are: (1) stem, (2) leaf, (3) leaf-bud, and (4) root cuttings.

Stem cuttings use portions of the stem containing terminal or lateral buds.

Stem cuttings can be made from herbaceous or softwood (tissues that are not lignified),

semihardwood (tissues that contain lignified tissue), deciduous hardwood (mature woody

stems), and conifer cuttings (tissues that are hardwood obtained from conifer plants

in early winter).

Examples of plants produced by the different types of cutting material including the following:

softwood or herbaceous stems from forsynthia, lilac, geranium, or carnation; semihardwood

from azalea, holly, or rhododendron; deciduous hardwood from hardwood trees; and conifer

stems from juniper, hemlock, or pine.

Leaf cuttings consist of a portion of a leaf blade, a complete leaf blade, or a leaf blade

with the petiole attached.

Leaf cuttings are typically used when plant materials are scarce and when large numbers

of plants are needed.

Following are examples of popular species propagated by leaf cuttings: Sansevieria (snake

plant) is very easy to propagate, but the cutting must be placed in the same orientation

it is found on the plant.

African violets are also easily propagated by detaching the leaf from the plant, inserting

the leaf into the soil, and sealing the container with the cutting in a clear plastic bag.

New roots and shoots will emerge from the base of the petiole.

Rex begonias can be easily propagated by detaching the leaf, making small cuts on several veins,

and pinning the leaf to the soil to assure that the leaf stays in contact with it.

The container with the cutting is sealed in a clear plastic bag to hold in moisture.

Plants will form roots at the cuts on each vein.

Leaf-bud cuttings consist of a leaf, petiole, and a short piece of stem with a lateral bud.

This type of propagation is very important when woody plant material is scarce and a

large number of new plants are required.

Leaf-bud cuttings are taken from plants with fully developed buds and actively growing

leaves.

Typically, as is the case with most hardwood cuttings, leaf-bud cuttings must be treated

with a rooting hormone prior to placement in the rooting medium.

The lateral bud should not be completely covered, because the bud will remain too moist and

rot.

To ensure success of rooting, the cuttings should also be placed under high humidity

and be supplied with bottom heat.

Examples of popular species that are propagated by leaf-bud cuttings are rhododendron, magnolia,

camellia, and maple.

Root cuttings are root pieces taken from young plants as a source of material.

Roots are dug in the winter or early spring, cleaned, cut 3 to 6 inches in length, and

treated with a fungicide.

Root cuttings are typically planted horizontally approximately 2 inches deep.

Although the regeneration of plants from root cuttings takes place in different ways, typically

the adventitious shoot is produced followed by the production of roots at the base of

the newly formed shoot.

Raspberries are commonly propagated by using root cuttings.

Root cuttings are not commonly done for most types of plants because root cutting is labor-intensive

and the plant produced can be different from the parent plant.

To ensure optimal rooting of cuttings, start with a high-quality parent plant.

Treatment of cuttings with the plant hormone auxin is used to initiate rooting.

Rooting hormone can come as a solution or powder.

The most common method immerses the basal end of the cutting approximately 1 inch into

the hormone then planted.

Although auxins are not effective in all plant species, there are several different benefits:

A higher percentage of the cuttings produce roots; root initiation is quicker in most

cases; the number and quality of roots per cutting is increased; and uniformity of rooting

along the length of the cutting is increased.

To be successful when attempting to root cuttings, five factors should be taken into consideration.

The parent plant used for cutting production must be grown under optimal cultural and environmental

conditions.

When parent plants are well nourished and growing vigorously, they generally produce

high-quality cuttings.

The time of the year and time of the day to harvest cuttings are very important.

Cuttings from herbaceous plants can be taken any time of the year, whereas hardwood cuttings

typically root better when materials are collected during the late winter when cuttings are dormant.

Softwood and semihardwood cuttings taken from deciduous plants should be taken in the spring

and midsummer, respectively.

Cuttings should always be harvested during the early morning, when plants are turgid.

Some plants are easy to root, whereas others are very difficult to root.

The plants that are easy to root typically require little or no special treatment (herbaceous

plants are generally easy to root).

Difficult-to-root plants, which are typically woody, require that the bark is scraped off

at the base of the cutting.

Both easy-to-root and difficult-to-root cuttings are typically treated with auxins to stimulate

rooting.

After the cutting is taken from the parent plant and properly prepared, the root-inducing

environment must be optimized to maximize rooting.

Cuttings do not have roots, so they cannot readily absorb moisture from the growing medium.

To prevent moisture loss from the cutting, maintain a high relative humidity around the

cuttings by misting them.

Immediately after sticking the cutting, misting is required frequently.

As time goes on, the frequency is reduced until finally misting is no longer needed.

To induce faster rooting, the use of bottom heat is very effective.

The temperature used for bottom heat should be about 10°F above the ambient air temperature,

which is typically maintained between 65 and 75°F. By supplying bottom heat, rooting occurs

faster than shoot growth, thereby producing a healthy rooted cutting.

Many species root very easily and can root in water alone; coleus is an excellent example.

Most plants, however, require a high-quality rooting medium for cuttings to root efficiently.

Sand, perlite, peat moss, and vermiculite can be used alone or in various combinations.

Fertilization should occur after the roots have emerged from cuttings.

In fact, fertilization prior to root emergence can actually inhibit or delay the rooting

process.

The proper time to transplant cuttings differs with the plant species used; however, a general

rule of thumb is when an adequate amount of root mass has formed to support plant growth.

When transplanting cuttings, carefully remove them from the rooting bed or container and

plant no deeper than they originally were planted.

Grafting is the process of connecting two plants or plant parts so they will unite and

continue to grow as one plant.

For the grafting process, one of the two plants being grafted must serve as the understock,

which is the bottom part of the graft union that is in contact with the soil.

The other component of the graft is the scion, which is a short piece of stem with one or

two buds.

For grafting to be successful, the scion and understock must be compatible, and the cambium

layers must be in close contact between the scion and understock.

Additional factors is that the understock must be equal to or larger then the scions

diameter and it must be done at the proper time of year so that the scion buds are dormant

but can still produce callus tissue.

Immediately after grafting, all cut surfaces must be thoroughly covered with grafting wax,

which is a water-repellent material composed of beeswax, resin, and tallow, to prevent

desiccation.

Grafting can be used: to maintain clones that cannot be propagated by other asexual methods;

to gain benefits of certain rootstocks, for example, disease-resistant and dwarfing rootstocks

are currently used; to speed up the time to maturity to promote earlier fruit production;

and to repair damaged parts of trees.

Grafting can be classified according to the part of the rootstock on which the scion is

placed, such as a root or various places on the top of the plant.

The three major categories of grafts are detached scion, approach, and repair grafting.

Detached scion grafting involves inserting a detached scion into the apex, side, bark,

or root of the understock; detached scion methods include apical, side, bark, and root

grafting.

There are six types of apical grafting.

The whip-and-tongue, splice, and saddle are used when the scion and stock are approximately

equal in size.

The cleft and wedge are used when the scion is smaller than the stock.

Side grafts place the scion on the side of the rootstock.

Side grafting is usually performed at the bench with the rootstock potted and just coming

out of dormancy and the scion is dormant.

There are three types of side grafting: side-stub, side-tongue, and side-veneer.

Side-veneer grafting is the most popular way to graft conifers, especially those having

a compact or dwarf form.

The bark graft and the inlay bark graft are types of grafts used for topworking established

plants.

Topworking is a technique used in fruit orchards for changing cultivars without having to plant

new trees.

The scions are inserted into the slot made by the removal of the bark.

The end of the scion is slipped under the raised flap of bark.

Two nails are driven through the scion, one going through the flap.

Root grafting (also called whole-root or piece-root grafting) uses only a root piece as the rootstock

compared to other types of grafts where the rootstock contains both root and stem tissue.

At one time, this was a common graft for apples.

Root grafting is done as bench grafting when the scion is dormant.

They are commonly tied with nursery tape that decomposes naturally when the graft is planted

in the soil.

Approach grafting is unique because both the rootstock and scion remain attached to their

root systems during the grafting process.

The scion is usually in a container, which is brought to the rootstock.

This grafting is done while both partners are actively growing.

It is a graft used when the scion is unique and the propagator does not want to remove

it from the stock plant.

It is also used when standard grafts have not been successful.

This type of grafting can be broken down into three categories: spliced approach, tongued

approach, and inlay approach.

Repair grafts are used to correct damage done to established trees.

The two most common repair grafts are bridge grafting and inarching.

These differ because in inarching, the rootstock has its own root system.

In bridge grafting, a scion is inserted around the injured section and attached at both the

upper and lowers ends of live, undamaged bark.

Budding is similar to grafting except that the scion is reduced to a single bud with

a small portion of bark or wood attached.

Budding methods are typically done in the spring or fall when the bark slipswhich

means that the bark separates easily from the wood (xylem)— and cambium cells are

actively dividing.

The three main types of budding are chip budding, T-budding, and patch budding.

Layering is a simple method of asexual propagation in which roots are formed on the stem while

still attached to the parent plant.

Layering occurs naturally in some species; a good example is the strawberry plant.

There are five types of layering commonly used in horticulture.

Simple layering occurs when the stem of a plant is gently curved, nicked at the bend,

placed in a shallow hole, and the terminal end of the shoot being buried is left exposed.

A new plant is formed at the location where the nick was made.

Serpentine layering occurs when the stem of a plant is gently curved at several locations.

Trench layering occurs when the middle portion of a flexible stem is buried in the soil after

nicking it at several locations.

Mound layering occurs when the parent plant is first cut back to slightly above ground

level in late winter and covered with soil.

The pruning causes new shoot growth to occur in the spring.

After this growth occurs in the spring, soil is mounded around the base of the shoot.

As the shoot grows, the additional soil is placed around the shoot and roots then develop

around the base of the shoot.

Air layering involves removing a portion of the bark on the stem, placing moist material

such as sphagnum moss around this wounded site, wrapping with clear plastic, and sealing

both ends to hold in moisture.

Camellias are commonly propagated using this method.

Separation occurs when a natural structure is removed from the parent plant and grows

on its own.

Examples are bulbs (tulips or lilies) or corms (gladiolus or crocus).

Division relies on cutting plant parts into sections as a means of propagation.

Examples are rhizomes like iris or tubers like Irish potatoes.

Tissue culture is a method for producing new plants from single cells, tissue, or pieces

of plant material called explants on artificial medium under sterile conditions.

Some commonly used methods of tissue culture are as follows.

Callus culture is the use of callus, which is an undifferentiated mass of cells that

can be induced naturally by wounding or artificially by using plant hormones as a means of growing

plants or different plant parts on a solid medium.

Cell suspension culture is a method in which plant cells are suspended in a liquid media

under continuous agitation to provide aeration.

Suspension cultures are initiated by placing callus in a liquid medium and agitating to

aerate and to disperse the cells.

Embryo culture (also called embryo rescue) occurs when the embryo is removed from the

seed aseptically and grown on a solid gel medium under optimal environmental, nutritional,

and hormonal conditions to promote growth of the embryo, which would not germinate within

the seed.

Meristem culture is a technique that uses the smallest part of the shoot tip as an explant,

which includes the meristem dome and some leaf primordia.

The meristem is a region of the plant consisting of undifferentiated tissue whose cells can

divide and differentiate to form specialized tissues.

In conclusion, asexual propagation is commonly used when sexual propagation is not an option.

There are nine commonly used types of asexual propagation and it depends on the plant on

which technique is best.

The Description of Asexual Plant Propagation