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Asexual reproduction in plants
Several plants reproduce sexually and asexually. When it comes to asexual reproduction in plants, part of the parent plants are used in order for a new plant to emerge. This can be done artificially by several methods and techniques designed by man. The new plant that emerges is usually identical to the parent plant from which the part used was taken. Asexual plants thrive well in stable environments compared to plants produced sexually.
Asexual reproduction in plants is advantageous in that the resulting plant mature faster since they emerge from an adult plant or part of the plant. Also reproducing asexually in plants makes the plant sturdier than seedlings from sexual reproduction. Nevertheless, asexual reproduction in plants can take place by two methods, which are:
- Natural methods of asexual reproduction
- Artificial method of asexual reproduction
The natural methods of asexual reproduction comprise of ways plants take on to propagate themselves. It involves asexual reproduction occurring naturally in plants without the interference of humans in the production and growth of the new plant.
Some plants grow continuously from buds on their stem surface e.g onion, ginger, dahlia, and gladioli, etc. In some plants, the adventitious roots or runners naturally reproduce new plants like in the sweet potato. The new plants may be reproduced naturally from the stems, roots, and leaves of the parent plant.
Vegetative plant structures such as rhizomes, runners, tubers, and bulbs arise from the plant. Runners, for instance, grow horizontally above the ground and forms buds at the nodes. Tubers are swollen modified roots and they give rise to new plants. Also, few plants have leaves that detach from the parent plant and give rise to new plants.
Bulbs have leaves that store food and have these leaves attached to an underground stem. There is an apical bud at the center of the bulb that produces flowers and leaves. The bulb then develops shoots from the lateral buds.
The artificial methods of asexual reproduction in plants don’t occur naturally. This involves methods of reproduction that are influenced by humans in the lab or on the fields. Here are some common types of artificial vegetative propagation:
- Tissue culture
This is an artificial method of asexual propagation in plants where the stem or leaf of another plant is attached to the stem of a plant that is rooted in the ground. Over time, the tissues of the rooted plant become integrated with the tissue of the graft and the graft develops as a single plant.
The grafted stem is called the scion while the root is referred to as the stock. In grafting, two plant species are used whereby the scion of the desired plant is grafted onto the stock of the other plant species. This is done by cutting the parts at an oblique angle and binding them together in a way that they are placed in close contact with each other.
It is very important to match the two surfaces together as close as possible in order to hold the plant together. The vascular tissues of the two plants eventually fuse and grow together to form a graft. Then, the scion after some time starts producing shoots that eventually bear fruits and flowers. It is common to see scions that have the ability to produce a particular variety of fruit being grated onto a rooted stock that has a specific resistance to disease.
This asexual method is used to produce plants that the favorable stem characteristics of a plant are combined with the favorable root characteristics of another plant. It has been used for a long time to reproduce novel varieties of plants such as citrus species, roses, etc. This grafting method is widely used in the citrus industry and viticulture (grape growing).
This method of artificial asexual reproduction involves cutting and planting a part of the plant, specifically a leaf or stem. Sometimes to even induce root development, these cuttings are treated with hormones and the new plant emerges from the adventitious roots that develop from the cutting.
Through stem cutting, some plants like the money plant and coleus are propagated. Usually, a part of the stem contains nodes and internodes that if placed in moist soil develop roots. In some plant species, the stem can even produce roots in water. A typical example is the leaves of the African violet that can root in water if kept undisturbed for many weeks.
This is an artificial method whereby a portion of the stem is bent and buried in the soil to form a new plant. In the method of layering, the plant’s stem is bent to the ground and is covered with soil for adventitious roots to emerge. The attached stem with these developing roots is called the layer. In this method, it is preferable to use young stems that can easily bend without any injury. Plants like jasmine and paper flowers (bougainvillea) are grown using this method.
A modified kind of layering called air layering is used in some plants. In this type of layering, a part of the stem covering or bark of the tree is removed and covered with moss, which is then taped. Rooting hormones can be applied as well by some gardeners. Eventually, roots begin to develop after some time and this part of the plant is then excavated and transplanted into a separate pot.
Micropropagation is an artificial method of reproduction where new plants are developed from culturing plant cells in the lab. This method is also known as plant tissue culture and is helpful because it increases the population of rare and endangered species of plants are may not be able to grow under natural conditions. Also, economically important plants and disease-free plants can be propagated via tissue culture.
In this method, a large number of plants are propagated from a single plant under lab conditions in a short period of time. A part of a plant like a leaf, anther, seed, embryo, or stem can be used to commence a plant tissue culture. A combination of chemical treatments that are standard for the plant species is used to sterilize the plant part used for the culture. The next process involves sterile conditions and the plant tissue culture medium where the plant part is then placed in. This plant tissue culture medium has essential minerals needed by the plant as well as hormones and vitamins.
The plant part culture then produces an undifferentiated mass called callus. After some time, individual plantlets begin to grow from this callus which is then separated and grown first under greenhouse conditions before taking them to the field.
Examples of Asexual Plants
These plants propagate themselves by using an asexual means of reproduction. Asexual reproduction in plants doesn’t need the usual sexual processes of flower production, sorting for means of seed dispersal or attracting pollinators. When plants reproduce asexually, the plants produced are identical to the parent plants. This is because there is no fusion of the male and female gamete in the process. As a result of carrying genes that are identical to their parents, they survive well under environmental conditions that are stable.
Several root types, stems, and modified leaves carry out asexual reproduction and this can be seen in common plants around us. For instance:
- Garlic, gladiolus, and crocuses (Crocus) use corm to reproduce asexually.
- Bulbs (scally bulbs) are used in lilies for asexual reproduction.
- The tunicate bulb is used in daffodils for asexual propagation.
- Adventitious roots can give rise to new plants like in the case of ivy.
- Some plants like the parsnip can propagate from the taproot.
- Potatoes and dahlia are stem tubers that reproduce by using underground tubers.
- The rhizome is an organ of asexual reproduction as its growing tips can separate as new plants such as in iris, ginger, nettles, and couch grass.
- The stolon also known as a runner are prostrate aerial stems that are used for asexual reproduction in plants like strawberry, some ferns, and numerous grasses.
- Adventitious buds can form on damaged stems, old roots, or roots that are near the surface of the ground. These buds can then develop into stems and leaves.
- Some plants are propagated asexually via their suckers such as in dandelion, elm, Rosa, and rubus.
- The leaves of plants like Bryophyllum and kalanchoe have small buds. The buds grow on the margins of the leaves and detach from the plant to grow into new independent plants. Also, new independent plants may grow when the leaves touch the soil.
- The underground bulbs of plants divide into more bulbs to reproduce new plants like onions, narcissus, hyacinth, and tulips.
- Asexual reproduction in some flowering plants involves the production of seeds without fertilization. This reproduction type is called apomixis and seed is formed asexually from the maternal tissues of the ovule resulting in the development of an embryo without meiosis and fertilization. This is common in plants like bryophytes, certain ferns, and lycopods.