- Vegetative propagation or vegetative reproduction is the growth and development of a plant by asexual means. This development occurs as a result of fragmentation and regeneration of a plant part or by growth from specialized vegetative plant parts.
- Many plants that reproduce asexually are also capable of sexual propagation. Vegetative propagation involves reproduction through vegetative (non-sexual) plant structures, whereas sexual propagation is accomplished through gamete production and fertilization.
In non-vascular plants, such as mosses and liverworts, vegetative reproductive structures include gemmae and spores. In vascular plants, vegetative reproductive plant parts include roots, stems, and leaves.
Meristem Tissue and Regeneration
Vegetative propagation is made possible by meristem tissue that is commonly found within stems and leaves, as well as at the tips of roots and stems. Meristem tissue contains undifferentiated cells that actively divide by mitosis allowing plant growth. Specialized, permanent plant tissue systems also originate from meristem tissue. It is this ability of meristem tissue to continue to divide that allows for the regeneration that is needed for vegetative propagation to occur.
Types of Vegetative Propagation
Vegetative propagation may be accomplished by natural (natural vegetative propagation) as well as artificial (artificial vegetative propagation) means. Since plants resulting from vegetative propagation are produced asexually from a single parent plant, they are genetic clones of the parent plant. This can have advantages and disadvantages. One advantage of vegetative propagation is that plants with traits that are favorable for a particular environment are repeatedly reproduced. Commercial crop growers employing artificial vegetative propagation techniques can ensure that favorable traits and product quality are maintained. A major disadvantage of vegetative propagation is that this process does not allow for genetic variation. The plants are genetically identical and are all susceptible to the same plant viruses and diseases that can destroy entire crops.
Natural vegetative propagation involves the development of a new plant from parts of a single mature plant. The new plants grow and develop naturally without human intervention. An important ability that is key to enabling vegetative propagation in plants is the ability to develop adventitious roots. These are roots that arise from plant structures other than the root, such as stems or leaves. Through the formation of adventitious roots, new plants may develop from extensions of the stems, roots, or leaves of a parent plant. Modified stems are most often the source of vegetative propagation in many plants. Vegetative plant structures that arise from plant stems include rhizomes, runners, bulbs, tubers, corms, and buds. Vegetative structures emanating from roots include buds and tubers. Plantlets are vegetative structures that emerge from plant leaves.
Vegetative propagation may occur naturally through the development of rhizomes. Rhizomes are modified stems that typically grow horizontally along the ground surface or underground. Rhizomes are storage sites for substances such as proteins and starches. As rhizomes extend, roots and shoots may arise along certain intervals 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, sometimes called stolons, are similar to rhizomes in that they exhibit horizontal growth at or just below the soil surface. Unlike rhizomes, they originate from existing stems. As runners grow, they develop roots and shoots from buds located at nodes or at runner tips. Intervals between nodes (internodes) are more widely spaced in runners than in rhizomes. New plants arise at nodes where roots and shoots develop. This type of propagation is seen in strawberry plants and currants.
Bulbs are 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 for the new plant. Examples of plants that develop from bulbs include onions, garlic, shallots, hyacinths, daffodils, lilies, and tulips.
Sweet potato sprouting new plants from the eyes. This is an example of vegetative propagation. Ed Reschke/Photolibrary/Getty Images
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 the tuber produces the new plant shoot system (stems and leaves), while the bottom surface produces the 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 are enlarged, bulb-like underground stems. These vegetative structures store nutrients in fleshy, solid stem tissue and are typically surrounded externally by papery scale-like leaves. Due to their external appearance, corms are commonly confused with bulbs. The major difference is that corms consist internally of solid tissue, while bulbs consist of layers of scale-like leaves. Corms produce adventitious roots and possess buds that develop into new plant shoots. Plants that develop from corms include crocus, gladiolus, and taro.
Suckers or root sprouts are plant shoots that arise from buds on underground roots or stems. Suckers may also sprout from buds near the base of the parent plant and can grow into new plants. A number of shrubs and trees propagate through sucker production. Some examples include apple trees, cherry trees, banana trees, hazel shrubs, roses, raspberries and gooseberries.
Plantlets are vegetative structures that develop on some plant leaves. These minature, young plants arise from meristem tissue located along leaf margins. Upon maturity, plantlets develop roots and drop from leaves. They take root in the soil forming new plants. An example of a plant that propagates in this manner is Kalanchoe or mother of thousand plant. Plantlets may also develop from the runners of certain plants such as spider plants.
Artificial Vegetative Propagation
Artificial vegetative propagation is a type of plant reproduction that is accomplished through artificial means involving human intervention. The most common types of artificial vegetative reproductive techniques involve cutting, layering, grafting, suckering, and tissue culture. 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 eventually 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. Eventually, the tissue systems of the cutting become grafted into or integrated with the tissue systems of the base plant.
- 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 develop in the parts covered by soil and the attached shoot (branch or stem) with new roots in 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. Adventitious roots develop where the branches were scrapped and the branches are removed from the tree and planted. The branches develop into new plants over time.
- Suckering – Suckers are allowed to grow forming a dense compact mat that is attached to the parent plant. Since too many suckers can lead to a smaller crop size, excess numbers are pruned. Mature suckers are cut away from the parent plant and transplanted to a new area where they grow into new plants.
- 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-ladened medium and eventually develops into plantlets. Plantlets can then be planted and develop into fully grown plants.