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Vegetative reproduction

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 obviously stretched by this process.
Vegetative reproduction from a stem cutting less than a week old. Some species are more conducive to this means of propagation than others.
A Muscari, or bulb, displaying vegetative reproduction.

Vegetative reproduction (vegetative propagation, vegetative multiplication, vegetative cloning) is a form of asexual reproduction in plants. It is a process by which new individuals arise without production of seeds or spores. It can occur naturally or be induced by horticulturists, in which case the technical process may require special care.

Although most plants normally reproduce sexually, they all have the ability for vegetative propagation. This is due to the fact that meristematic cells can differentiate according to stage of growth, location on the plant and environmental conditions. Horticulturalists are interested in understanding and affecting those factors in order to optimize the process.

Success rates and difficulty of propagation vary greatly. For example willow and coleus can be propagated merely by inserting a stem in water or moist soil. On the other hand, monocotyledons, unlike dicotyledons, typically lack a vascular cambium and therefore are harder to propagate.

Contents

[edit] Types

In a wide sense, methods of vegetative propagation include cutting, Vegetative apomixis, layering, division, budding, grafting and tissue culture. Cutting is the most common artificial vegetative propagation method, where pieces of the "parent" plant are removed and placed in a suitable environment so that they can grow into a whole new plant, the "clone", which is genetically identical to the parent. Cutting exploits the ability of plants to grow adventitious roots (i.e. root material that can generate from a location other than the existing or primary root system, as in from a leaf or cut stem) under certain conditions.

Vegetative propagation is usually considered a cloning method. However, there are several cases where vegetatively propagated plants are not genetically identical. Rooted stem 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. Leaf cutting propagation of certain chimeral variegated plants, such as snake plant, will produce mainly nonvariegated plants.

Grafting is often not a complete cloning method because sexual 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 asexual reproduction involving unfertilized seeds. Hawkweed (Hieracium), dandelion (Taraxacum), some Citrus (Citrus) and Kentucky blue grass (Poa pratensis) all use this form of asexual reproduction. Bulbils are sometimes formed in the flowers of garlic. The leafy crown of a pineapple fruit will root to form a new plant. These cases would not be vegetative reproduction because normally reproductive parts were involved. They would be considered asexual reproduction however. Vegetative reproduction involves only vegetative structures, i.e. roots, stems or leaves.

[edit] Vegetative structures

Virtually all types of shoots and roots are capable of vegetative propagation, including stems, basal shoots, tubers, rhizomes, stolons, corms, bulbs and buds.

  • The rhizome is a modified underground stem serving as an organ of vegetative reproduction, e. g. Polypody, Iris, Couch Grass and Nettles.
  • Prostrate aerial stems, called runners or stolons are important vegetative reproduction organs in some species, such as the strawberry, numerous grasses, and some ferns.
  • Adventitious buds form on roots near the ground surface, on damaged stems (as on the stumps of cut trees), or on old roots. These develop into above-ground stems and leaves.
  • A form of budding called suckering is the reproduction or regeneration of a plant by shoots that arise from an existing root system. Species that characteristically produce suckers include Elm (Ulmus), Dandelion (Taraxacum), and members of the Rose Family (Rosa).
  • Another type of a vegetative reproduction is the production of bulbs. Plants like onion (Allium cepa), hyacinth (Hyacinth), narcissus (Narcissus) and tulips (Tulipa) reproduce by forming bulbs.
  • Other plants like potatoes (Solanum tuberosum) and dahlia (Dahlia) reproduce by a method similar to bulbs: they produce tubers.
  • Gladioli and crocuses (Crocus) reproduce by forming a bulb-like structure called a corm.

[edit] Natural vegetative propagation

Natural vegetative reproduction 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 or a root) can contribute to vegetative reproduction of a plant. And, in a few species (such as Kalancho√« shown at right), leaves are involved in vegetative reproduction. 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.

[edit] Artificial vegetative propagation

Man-made methods of vegetative reproduction are usually enhancements of natural processes, but range from simple cloning such as rooting of cuttings to grafting and artificial propagation by laboratory tissue cloning. It is very commonly practised to propagate cultivars with individual desirable characteristics. Fruit tree propagation is frequently performed by budding or grafting desirable cultivars (clones), onto rootstocks that are also clones, propagated by layering.

In horticulture, a "cutting" is a branch that has been cut off from a mother plant below an internode and then rooted, often with the help of a rooting liquid or powder containing hormones. When a full root has formed and leaves begin to sprout anew, the clone is a self-sufficient plant, genetically identical to the mother plant. Examples are cutting from the stems of blackberries (Rubus occidentalis), cutting from leaves of African violets (Saintpaulia), and cutting the stems of verbenas (Verbena) to create new plants. A related form of regeneration is that of grafting. This is a process of taking a bud and grafting onto a plants stem. Many nurseries now sell trees that can produce four or more varieties of apples (Malus spp.) from stems grafted to a common rootstock.

[edit] Cultivated plants propagated by vegetative methods

A number of commonly cultivated plants are propagated by vegetative means rather than by seeds. This is a listing of such plants:

Apple
Avocado
Canna
Cannabis
Citrus (lemon, orange, grapefruit)
Date
Fig
Grapes
Hops
Manioc (cassava)
Nut crops (walnut, pecan)
Pineapple
Pear
Poplar
Potato
Strawberry
Sugar cane
Tea
Vanilla
Willow

[edit] See also



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