Vegetative reproduction

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Production of new individuals along a leaf margin of the air plant, Kalanchoe pinnata. The small plant in front is about 1 cm tall. The concept of "individual" is stretched by this process. Kalanchoe veg.jpg
Production of new individuals along a leaf margin of the air plant, Kalanchoe pinnata . The small plant in front is about 1 cm tall. The concept of "individual" is stretched by this process.
Kalanchoe daigremontiana produces plantlets along the margins of its leaves. When they are mature enough, they drop off and root in any suitable soil beneath. Bryophyllum daigremontianum nahaufnahme1.jpg
Kalanchoe daigremontiana produces plantlets along the margins of its leaves. When they are mature enough, they drop off and root in any suitable soil beneath.
Vegetative reproduction from a stem cutting less than a week old. Some species are more conducive to this means of propagation than others. Stem Cutting.jpg
Vegetative reproduction from a stem cutting less than a week old. Some species are more conducive to this means of propagation than others.
A bulb of Muscari has reproduced vegetatively underground to make two bulbs, each of which produces a flower stem. Muscari displaying vegetative reproduction.JPG
A bulb of Muscari has reproduced vegetatively underground to make two bulbs, each of which produces a flower stem.

Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is a form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or specialized reproductive structures, which are sometimes called vegetative propagules. [1] [2] [3]

Contents

Many plants naturally reproduce this way, but it can also be induced artificially. Horticulturists have developed asexual propagation techniques that use vegetative propagules to replicate plants. Success rates and difficulty of propagation vary greatly. Monocotyledons typically lack a vascular cambium, making them more challenging to propagate.

Background

Plant propagation is the process of plant reproduction of a species or cultivar, and it can be sexual or asexual. It can happen through the use of vegetative parts of the plants, such as leaves, stems, and roots to produce new plants or through growth from specialized vegetative plant parts. [4]

While many plants reproduce by vegetative reproduction, they rarely exclusively use that method to reproduce. Vegetative reproduction is not evolutionary advantageous; it does not allow for genetic diversity and could lead plants to accumulate deleterious mutations. [5] Vegetative reproduction is favored when it allows plants to produce more offspring per unit of resource than reproduction through seed production. [6] In general, juveniles of a plant are easier to propagate vegetatively. [7]

Although most plants normally reproduce sexually, many can reproduce vegetatively, or can be induced to do so via hormonal treatments. This is because meristematic cells capable of cellular differentiation are present in many plant tissues.

Vegetative propagation is usually considered a cloning method. [8] However, root cuttings of thornless blackberries ( Rubus fruticosus ) will revert to thorny type because the adventitious shoot develops from a cell that is genetically thorny. Thornless blackberry is a chimera, with the epidermal layers genetically thornless but the tissue beneath it genetically thorny. [9]

Grafting is often not a complete cloning method because seedlings are used as rootstocks. In that case, only the top of the plant is clonal. In some crops, particularly apples, the rootstocks are vegetatively propagated so the entire graft can be clonal if the scion and rootstock are both clones. Apomixis (including apospory and diplospory) is a type of reproduction that does not involve fertilization. In flowering plants, unfertilized seeds are produced, or plantlets that grow instead of flowers. Hawkweed ( Hieracium ), dandelion ( Taraxacum ), some citrus ( Citrus ) and many grasses such as Kentucky bluegrass ( Poa pratensis ) all use this form of asexual reproduction. Bulbils are sometimes formed instead of the flowers of garlic.

Mechanisms

Meristem tissue makes the process of asexual reproduction possible. It is normally found in stems, leaves, and tips of stems and roots and consists of undifferentiated cells that are constantly dividing allowing for plant growth and give rise to plant tissue systems. The meristem tissue's ability to continuously divide allows for vegetative propagation to occur. [10]

Another important ability that allows for vegetative propagation is the ability to develop adventitious roots which arise from other vegetative parts of the plants such as the stem or leaves. These roots allow for the development of new plants from body parts from other plants. [11]

Advantages and disadvantages

Advantages

There are several advantages of vegetative reproduction, mainly that the produced offspring are clones of their parent plants. If a plant has favorable traits, it can continue to pass down its advantageous genetic information to its offspring. It can be economically beneficial for commercial growers to clone a certain plant to ensure consistency throughout their crops. [12] Vegetative propagation also allows plants to avoid the costly and complex process of producing sexual reproduction organs such as flowers and the subsequent seeds and fruits. [13] For example, developing an ace cultivar is extremely difficult, so, once farmers develop the desired traits in lily, they use grafting and budding to ensure the consistency of the new cultivar and its successful production on a commercial level. However, as can be seen in many variegated plants, this does not always apply, because many plants actually are chimeras and cuttings might reflect the attributes of only one or some of the parent cell lines. Vegetative propagation also allows plants to circumvent the immature seedling phase and reach the mature phase faster. [14] In nature, that increases the chances for a plant to successfully reach maturity, and, commercially, it saves farmers a lot of time and money as it allows for faster crop overturn. [15]

Vegetative reproduction offers research advantages in several areas of biology and has practical usage when it comes to afforestation. The most common use made of vegetative propagation by forest geneticists and tree breeders has been to move genes from selected trees to some convenient location, usually designated a gene bank, clone bank, clone-holding orchard, or seed orchard where their genes can be recombined in pedigreed offspring. [15]

Some analyses suggest that vegetative reproduction is a characteristic which makes a plant species more likely to become invasive. Since vegetative reproduction is often faster than sexual reproduction, it "quickly increases populations and may contribute to recovery following disturbance" (such as fires and floods). [16]

Disadvantage

A major disadvantage of vegetative propagation is that it prevents species genetic diversity which can lead to reductions in crop yields. [17] [18] The plants are genetically identical and are all, therefore, susceptible to pathogenic plant viruses, bacteria and fungi that can wipe out entire crops. [19]

Types

Natural means

Natural vegetative propagation is mostly a process found in herbaceous and woody perennial plants, and typically involves structural modifications of the stem, although any horizontal, underground part of a plant (whether stem, leaf, or root) can contribute to vegetative reproduction of a plant. Most plant species that survive and significantly expand by vegetative reproduction would be perennial almost by definition, since specialized organs of vegetative reproduction, like seeds of annuals, serve to survive seasonally harsh conditions. A plant that persists in a location through vegetative reproduction of individuals over a long period of time constitutes a clonal colony.

In a sense, this process is not one of reproduction but one of survival and expansion of biomass of the individual. When an individual organism increases in size via cell multiplication and remains intact, the process is called "vegetative growth". However, in vegetative reproduction, the new plants that result are new individuals in almost every respect except genetic. Of considerable interest is how this process appears to reset the aging clock. [20]

As previously mentioned, plants vegetatively propagate both artificially and naturally. Most common methods of natural vegetative reproduction involve the development of a new plant from specialized structures of a mature plant. In addition to adventitious roots, roots that arise from plant structures other than the root, such as stems or leaves, modified stems, leaves and roots play an important role in plants' ability to naturally propagate. The most common modified stems, leaves and roots that allow for vegetative propagation are: [21]

Runners

'Lipstick' hybrid strawberry (Comarum palustre x Fragaria x ananassa) using stolons to grow new plants Fragaria hybrid Lipstick.jpg
'Lipstick' hybrid strawberry (Comarum palustre × Fragaria × ananassa) using stolons to grow new plants

Also known as stolons, runners are modified stems that, unlike rhizomes, grow from existing stems just below the soil surface. As they are propagated, the buds on the modified stems produce roots and stems. Those buds are more separated than the ones found on the rhizome. [22]

Examples of plants that use runners are strawberries and currants.

Bulbs

Bulbs are inflated parts of the stem within which lie the central shoots of new plants. They are typically underground and are surrounded by plump and layered leaves that provide nutrients to the new plant. [23]

Examples of plants that use bulbs are shallots, lilies and tulips.

Tubers

Tubers develop from either the stem or the root. Stem tubers grow from rhizomes or runners that swell from storing nutrients while root tubers propagate from roots that are modified to store nutrients and get too large and produce a new plant. [22]

Examples of stem tubers are potatoes and yams and examples of root tubers are sweet potatoes and dahlias.

Corms

Corms are solid enlarged underground stems that store nutrients in their fleshy and solid stem tissue and are surrounded by papery leaves. Corms differ from bulbs in that their centers consists of solid tissue while bulbs consist of layered leaves. [24]

Examples of plants that use corms are gladiolus and taro.

Suckers

Also known as root sprouts, suckers are plant stems that arise from buds on the base of the parent plant's stems or roots. [25]

Examples of plants that use suckers are apple, elm, and banana trees.

Plantlets

Plantlets are miniature structures that arise from meristem in leaf margins that eventually develops roots and drop from the leaves they grew on. [26]

An example of a plant that uses plantlets is the Bryophyllum daigremontianum (syn. Kalanchoe daigremontianum), which is also known as mother of thousands for its many plantlets.

Keikis

Keikis are additional offshoots which develop on vegetative stems or flower stalks of several orchids genera. [14]

Examples of plants that use keikis are the Phalaenopsis , Epidendrum , and Dendrobium genera of orchids.

Apomixis

Apomixis is the process of asexual reproduction through seed, in the absence of meiosis and fertilization, generating clonal progeny of maternal origin. [27]

Artificial means

Vegetative propagation of particular cultivars that have desirable characteristics is very common practice. It is used by farmers and horticulturalists to produce better crops with desirable qualities. The most common methods of artificial vegetative propagation are: [21]

Cutting

A cutting is a part of the plant, usually a stem or a leaf, is cut off and planted. Adventitious roots grow from cuttings and a new plant eventually develops. Usually those cuttings are treated with hormones before being planted to induce growth. [28]

Grafting

Grafting involves attaching a scion, or a desired cutting, to the stem of another plant called stock that remains rooted in the ground. Eventually both tissue systems become grafted or integrated and a plant with the characteristics of the grafted plant develops, [29] e.g. mango, guava, etc.

Layering

Layering is a process which includes the bending of plant branches or stems so that they touch the ground and are covered with soil. Adventitious roots develop from the underground part of the plant, which is known as the layer. This method of vegetative reproduction also occurs naturally. Another similar method, air layering, involved the scraping and replanting of tree branches which develop into trees. Examples are Jasmine and Bougainvillea. [30]

Suckering

Suckers grow and form a dense compact mat that is attached to the parent plant. Too many suckers can lead to smaller crop size, so excess suckers are pruned, and mature suckers are transplanted to a new area where they develop into new plants. [31]

Tissue culture

In tissue culture, plant cells are taken from various parts of the plant and are cultured and nurtured in a sterilized medium. The mass of developed tissue, known as the callus, is then cultured in a hormone-ladened medium and eventually develops into plantlets which are then planted and eventually develop into grown plants. [12] [32]

An offset is the lower part of a single culm with the rhizome axis basal to it and its roots. Planting of these is the most convenient way of propagating bamboo.

See also

Related Research Articles

<span class="mw-page-title-main">Tuber</span> Storage organ in plants

Tubers are a type of enlarged structure used as storage organs for nutrients in some plants, usually stems, but some definitions refer to roots. Tubers help plants perennate, provide energy and nutrients, and are a means of asexual reproduction.

<span class="mw-page-title-main">Plant propagation</span> Process of growing new plants

Plant propagation is the process by which new plants grow from various sources, including seeds, cuttings, and other plant parts. Plant propagation can refer to both man-made or natural dispersal of seeds.

<span class="mw-page-title-main">Clonal colony</span> Genetically identical, single site plants, fungi, or bacteria

A clonal colony or genet is a group of genetically identical individuals, such as plants, fungi, or bacteria, that have grown in a given location, all originating vegetatively, not sexually, from a single ancestor. In plants, an individual in such a population is referred to as a ramet. In fungi, "individuals" typically refers to the visible fruiting bodies or mushrooms that develop from a common mycelium which, although spread over a large area, is otherwise hidden in the soil. Clonal colonies are common in many plant species. Although many plants reproduce sexually through the production of seed, reproduction occurs by underground stolons or rhizomes in some plants. Above ground, these plants most often appear to be distinct individuals, but underground they remain interconnected and are all clones of the same plant. However, it is not always easy to recognize a clonal colony especially if it spreads underground and is also sexually reproducing.

<span class="mw-page-title-main">Aerial root</span> Root which grows above the ground

Aerial roots are roots above the ground. They are almost always adventitious. They are found in diverse plant species, including epiphytes such as orchids (Orchidaceae), tropical coastal swamp trees such as mangroves, banyan figs, the warm-temperate rainforest rata, and pohutukawa trees of New Zealand. Vines such as common ivy and poison ivy also have aerial roots.

<span class="mw-page-title-main">Stolon</span> Horizontal connections between organisms

In biology, stolons, also known as runners, are horizontal connections between parts of an organism. They may be part of the organism, or of its skeleton. Typically, animal stolons are exoskeletons.

<span class="mw-page-title-main">Micropropagation</span> Practice in plant tissue culture

Micropropagation or tissue culture is the practice of rapidly multiplying plant stock material to produce many progeny plants, using modern plant tissue culture methods.

Fragmentation in multicellular or colonial organisms is a form of asexual reproduction or cloning, where an organism is split into fragments upon maturation and the spilted part becomes the new individual.

<span class="mw-page-title-main">Layering</span> Plant propagation technique

Layering is a vegetative propagation technique where the stem or branch of a plant is manipulated to promote root development while still attached to the parent plant. Once roots are established, the new plant can be detached from the parent and planted. Layering is utilized by horticulturists to propagate desirable plants.

<span class="mw-page-title-main">Cutting (plant)</span> Method of propagating plants

A plant cutting is a piece of a plant that is used in horticulture for vegetative (asexual) propagation. A piece of the stem or root of the source plant is placed in a suitable medium such as moist soil. If the conditions are suitable, the plant piece will begin to grow as a new plant independent of the parent, a process known as striking. A stem cutting produces new roots, and a root cutting produces new stems. Some plants can be grown from leaf pieces, called leaf cuttings, which produce both stems and roots. The scions used in grafting are also called cuttings.

Plant breeders use different methods depending on the mode of reproduction of crops, which include:

In biology, a propagule is any material that functions in propagating an organism to the next stage in its life cycle, such as by dispersal. The propagule is usually distinct in form from the parent organism. Propagules are produced by organisms such as plants, fungi, and bacteria.

<span class="mw-page-title-main">Plantlet</span> Young or small plant

A plantlet is a young or small plant, produced on the leaf margins or the aerial stems of another plant.

A seedless fruit is a fruit developed to possess no mature seeds. Since eating seedless fruits is generally easier and more convenient, they are considered commercially valuable.

<span class="mw-page-title-main">Basal shoot</span> Shoot growing from an adventitious bud

Basal shoots, root sprouts, adventitious shoots, and suckers are words for various kinds of shoots that grow from adventitious buds on the base of a tree or shrub, or from adventitious buds on its roots. Shoots that grow from buds on the base of a tree or shrub are called basal shoots; these are distinguished from shoots that grow from adventitious buds on the roots of a tree or shrub, which may be called root sprouts or suckers. A plant that produces root sprouts or runners is described as surculose. Water sprouts produced by adventitious buds may occur on the above-ground stem, branches or both of trees and shrubs. Suckers are shoots arising underground from the roots some distance from the base of a tree or shrub.

Plant reproduction is the production of new offspring in plants, which can be accomplished by sexual or asexual reproduction. Sexual reproduction produces offspring by the fusion of gametes, resulting in offspring genetically different from either parent. Asexual reproduction produces new individuals without the fusion of gametes, resulting in clonal plants that are genetically identical to the parent plant and each other, unless mutations occur.

<span class="mw-page-title-main">Grafting</span> Horticultural technique of joining plant tissues to grow together

Grafting or graftage is a horticultural technique whereby tissues of plants are joined so as to continue their growth together. The upper part of the combined plant is called the scion while the lower part is called the rootstock. The success of this joining requires that the vascular tissues grow together. The natural equivalent of this process is inosculation. The technique is most commonly used in asexual propagation of commercially grown plants for the horticultural and agricultural trades. The scion is typically joined to the rootstock at the soil line; however, top work grafting may occur far above this line, leaving an understock consisting of the lower part of the trunk and the root system.

Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues. By contrast, an animal embryo will very early produce all of the body parts that it will ever have in its life. When the animal is born, it has all its body parts and from that point will only grow larger and more mature. However, both plants and animals pass through a phylotypic stage that evolved independently and that causes a developmental constraint limiting morphological diversification.

<span class="mw-page-title-main">Plant tissue culture</span> Growing cells under lab conditions

Plant tissue culture is a collection of techniques used to maintain or grow plant cells, tissues, or organs under sterile conditions on a nutrient culture medium of known composition. It is widely used to produce clones of a plant in a method known as micropropagation. Different techniques in plant tissue culture may offer certain advantages over traditional methods of propagation, including:

<span class="mw-page-title-main">Vivipary</span> Plant seeds developing before detachment

In plants, vivipary occurs when seeds or embryos begin to develop before they detach from the parent. Plants such as some Iridaceae and Agavoideae grow cormlets in the axils of their inflorescences. These fall and in favourable circumstances they have effectively a whole season's start over fallen seeds. Similarly, some Crassulaceae, such as Bryophyllum, develop and drop plantlets from notches in their leaves, ready to grow. Such production of embryos from somatic tissues is asexual vegetative reproduction that amounts to cloning.

Nurse grafting is a method of plant propagation that is used for hard-to-root plant material. If a desirable selection cannot be grown from seed, it must be propagated asexually (cloned) in order to be genetically identical to the parent. Nurse grafting allows a scion to develop its own roots instead of being grafted to a rootstock.

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