Vegetative reproduction
Vegetative reproduction is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment of the parent plant or a specialized reproductive structure.
Many plants naturally reproduce this way, but it can also be induced artificially. Horticulturalists have developed asexual propagation techniques that use vegetative plant parts to replicate plants. Success rates and difficulty of propagation vary greatly. Monocotyledons typically lack a vascular cambium and therefore are harder to propagate.
Background
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.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. Vegetative reproduction is favored when it allows plants to produce more offspring per unit of resource than reproduction through seed production. In general, juveniles of a plant are easier to propagate vegetatively.
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. However, root cuttings of thornless blackberries 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..
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 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, dandelion, some citrus and many grasses such as Kentucky bluegrass 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.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.
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. 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. 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. 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.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.
Disadvantage
A major disadvantage of vegetative propagation is that it prevents species genetic diversity which can lead to reductions in crop yields. The plants are genetically identical and are all, therefore, susceptible to pathogenic plant viruses, bacteria and fungi that can wipe out entire crops.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 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.
As aforementioned, plants vegetetatively propagate both artificially and naturally. Most common methods of natural vegetative reproduction involves 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:
Runners
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.Examples of plants that use runners are strawberries and currants.
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.Examples of plants that use bulbs are shallots, lilies and tulips.
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.Examples of stem tubers are potatoes and yams and examples of root tubers are sweet potatoes and dahlias.
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.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 parent plants stems or on roots.Examples of plants that use suckers are apple, elm, and banana trees.
Plantlets
are miniature structures that arise from meristem in leaf margins that eventually develops roots and drop from the leaves they grew on.An example of a plant that uses plantlets is the Bryophyllum daigremontianum, which is also known as mother of thousands for its many plantlets.
Keikis
are additional offshoots which develop on vegetative stems or flower stalks of several orchids genera.Examples of plants that use keikis are the Phalaenopsis, Epidendrum, and Dendrobium genera of orchids.
Apomixis
is the process of asexual reproduction through seed, in the absence of meiosis and fertilization, generating clonal progeny of maternal origin.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: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.Example: rose;hibiscus.