Types of Vegetative Propagation

Plantlets - Vegetative Propagation
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Vegetative propagation or vegetative reproduction is the growth and development of a plant by asexual means. This development occurs through the fragmentation and regeneration of specialized vegetative plant parts. Many plants that reproduce asexually are also capable of sexual propagation.

The Process of Vegetative Propagation

Vegetative reproduction involves vegetative or non-sexual plant structures, whereas sexual propagation is accomplished through gamete production and subsequent fertilization. In non-vascular plants such as mosses and liverworts, vegetative reproductive structures include gemmae and spores. In vascular plants, vegetative reproductive structures include roots, stems, and leaves.

Vegetative propagation is made possible by meristem tissue, commonly found within stems and leaves as well as the tips of roots, that contains undifferentiated cells. These cells actively divide by mitosis to allow widespread and rapid primary plant growth. Specialized, permanent plant tissue systems also originate from meristem tissue. It is the ability of meristem tissue to continually divide that allows for plant regeneration required by vegetative propagation.

Advantages and Disadvantages

Because vegetative propagation is a form of asexual reproduction, plants produced through this system are genetic clones of a parent plant. This uniformity has advantages and disadvantages.

One advantage of vegetative propagation is that plants with favorable traits are repeatedly reproduced. Commercial crop growers can employ artificial vegetative propagation techniques to ensure advantageous qualities in their crops.

A major disadvantage, however, of vegetative propagation is that it does not allow for any degree of genetic variation. Plants that are genetically identical are all susceptible to the same viruses and diseases and crops produced through this method are, therefore, easily wiped out.

Types of Vegetative Propagation

Vegetative propagation may be accomplished by artificial or natural means. Though both methods involve the development of a plant from parts of a single mature part, the way that each is carried out looks very different.

Artificial Vegetative Propagation

Artificial vegetative propagation is a type of plant reproduction that involves human intervention. The most common types of artificial vegetative reproductive techniques include cutting, layering, grafting, suckering, and tissue culturing. These methods are employed by many farmers and horticulturists to produce healthier crops with more desirable qualities.

  • Cutting: A part of a plant, typically a stem or leaf, is cut off and planted. Adventitious roots develop from the cuttings and a new plant forms. Cuttings are sometimes treated with hormones before being planted to induce root development.
  • Grafting: In grafting, a desired cutting or scion is attached to the stem of another plant that remains rooted in the ground. The tissue systems of the cutting become grafted into or integrated with the tissue systems of the base plant over time.
  • Layering: This method involves bending plant branches or stems so that they touch the ground. The portions of branches or stems in contact with the ground are then covered with soil. Adventitious roots or roots that extend from structures other than plant roots develop in the parts covered by soil and the attached shoot (branch or stem) with new roots is known as a layer. This type of layering also occurs naturally. In another technique called air layering, branches are scraped and covered with plastic to reduce moisture loss. New roots develop where the branches were scraped and the branches are removed from the tree and planted.
  • Suckering: Suckers attach to a parent plant and form a dense, compact mat. Since too many suckers can lead to smaller crop size, excess numbers are pruned. Mature suckers are cut away from a parent plant and transplanted to a new area where they sprout new plants. Suckering has the dual purpose of growing new shoots and removing nutrient-sucking buds that prohibit a main plant from growing.
  • Tissue Culture: This technique involves the culturing of plant cells that may be taken from different parts of a parent plant. The tissue is placed in a sterilized container and nurtured in a special medium until a mass of cells known as a callus is formed. The callus is then cultured in a hormone-laden medium and eventually develops into plantlets. When planted, these mature into fully grown plants.

Natural Vegetative Propagation

Natural vegetative propagation happens when plants grow and develop naturally without human intervention. An important ability that is key to enabling natural vegetative propagation in plants is the ability to develop adventitious roots.

Through the formation of adventitious roots, new plants may sprout from stems, roots, or leaves of a parent plant. Modified stems are most often the source of vegetative plant propagation. Vegetative plant structures that arise from plant stems include rhizomes, runners, bulbs, tubers, and corms. Tubers can also stretch from roots. Plantlets emerge from plant leaves.

Plant Structures That Enable Natural Vegetative Propagation

Rhizomes

Vegetative propagation may occur naturally through the development of rhizomes. Rhizomes are modified stems that typically grow horizontally along the surface of or beneath the ground. Rhizomes are storage sites for growth substances such as proteins and starches. As rhizomes extend, roots and shoots may arise from segments of the rhizome and develop into new plants. Certain grasses, lilies, irises, and orchids propagate in this manner. Edible plant rhizomes include ginger and turmeric.

Runners

Strawberry Plant Runners
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Runners, also called stolons, are similar to rhizomes in that they exhibit horizontal growth at or just below the soil's surface. Unlike rhizomes, they originate from existing stems. As runners grow, they develop roots from buds located at nodes or their tips. Intervals between nodes (internodes) are more widely spaced in runners than in rhizomes. New plants arise at nodes where shoots develop. This type of propagation is seen in strawberry plants and currants.

Bulbs

Plant Bulb
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Bulbs are the round, swollen parts of a stem that are typically found underground. Within these organs of vegetative propagation lies the central shoot of a new plant. Bulbs consist of a bud that is surrounded by layers of fleshy, scale-like leaves. These leaves are a source of food storage and provide nourishment to the new plant. Examples of plants that develop from bulbs include onions, garlic, shallots, hyacinths, daffodils, lilies, and tulips.

Tubers

Sweet Potato Sprouting
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Tubers are vegetative organs that may develop from stems or roots. Stem tubers arise from rhizomes or runners that become swollen from storing nutrients. The upper surface of a tuber produces a new plant shoot system (stems and leaves), while the bottom surface produces a root system. Potatoes and yams are examples of stem tubers. Root tubers originate from roots that have been modified to store nutrients. These roots become enlarged and may give rise to a new plant. Sweet potatoes and dahlias are examples of root tubers.

Corms

Crocus sativus Corms
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Corms are enlarged bulb-like underground stems. These vegetative structures store nutrients in fleshy, solid stem tissue and are typically externally surrounded by papery leaves. Due to their physical appearance, corms are commonly confused with bulbs. The major difference is that corms contain solid tissue internally and bulbs have only layers of leaves. Corms produce adventitious roots and possess buds that develop into new plant shoots. Plants that develop from corms include crocus, gladiolus, and taro.

Plantlets

Kalanchoe - Plantlets
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Plantlets are vegetative structures that develop on some plant leaves. These miniature, young plants arise from meristem tissue located along leaf margins. Upon maturity, plantlets develop roots and drop from leaves. They then take root in the soil to form new plants. An example of a plant that propagates in this manner is Kalanchoe. Plantlets may also develop from the runners of certain plants such as spider plants.