In flowering plants, there are two main types of Recurrent Apomixis:
There are three different types of Agamospermy:
(i) Diplospory
In this method, archesporium differentiates to form a megaspore mother cell but this megaspore mother cell directly gives rise to an embryo sac without meiosis. This embryo sac is diploid and a diploid embryo is formed without fertilization from the diploid egg of this embryo sac.
Example: Parthenium, Taraxacum.
(ii) Adventive Embryony
In this method, an embryo is formed from any diploid cells (Nucleus or integuments) of the ovule except the embryo sac. This diploid cell behaves like a zygote. Adventive embryony derived from Nucleus in Citrus, Mangifera, Opuntia, Mamillaria and from Integuments in Spiranthus australis.
(iii) Apospory
It is discovered by Rosenberg in the Heiarcium plant. In this method embryo sac or female gametophyte is directly formed from any diploid cell of the sporophyte except megaspore mother cell without meiosis is known as apospory. In this, gametophyte always remains diploid.
Example: Hieracium, Ranunculus and Rubus.
Generally, the method of vegetative propagation have been further divided into two types:
(i) Natural Vegetative Propagation
(a) By Roots: The modified tuberous root of Sweet potato (Ipomoea batatas), Asparagus, Tapioca, Yam, Dahlia and Tinospora can be propagated vegetatively when planted in soil. In some plants, adventitious buds develop on the ordinary roots like - Dalbergiasisso, Populus, Guava, Murraya, Albizzia lebbek etc. which grow to form new plants. The buds present on the roots grow into leafy shoot above the ground is called Slips.
Natural Vegetative Propagation in Sweet Potato(b) Underground Stem: In some plants underground modified stem such as - Rhizomes - Typha; Canna, Ginger, Turmeric, Lotus, Musa etc. Corm - Gladiolus, Colocasia, Crocus, Amorphophallus, Alocasia etc. Bulbs - Onion, Garlic and Lilies Tubers - Potato, Helianthus tuberosus etc. which grow to form a new plant. Sucker - Mint and Chrysanthemum.
(c) Creepers: In the creeping stem of the plants' adventitious root is developed from the nodes and to form aerial shoots such as:
(d) Leaves: Some plants produce adventitious buds on their leaves.
Examples: Bryophyllum, Begonia, Streptocarpus, Saintpaulia.
Vegetative Propagation on Leaf of BryophyllumThese buds remain dormant when the leaves attached with plants but after separation, when it comes in contact with moist soil develop new plantlets (buds) which form new plants.
In the Kalanchoe plant, the whole portion of the leaf blade regenerates a new plant.
In some of the plants, fleshy axillary buds that develop from the axis of leaves are called Bulbils.
Examples: Dioscorea, Oxalis, Dentaria, Globba, Agave, Lilium.
There is a special type of fleshy buds that develop in the Aquatic plant, called Turions.
Examples: Potamogeton, Utricularia.
(ii) Artificial Propagation
Gardeners and Horticulturist have employed various method of vegetative propagation for economic production. All the methods are man-made so that their practices constitute artificial means of vegetative propagation.
These are as follows:
(i) Cutting: A cutting is a separated portion of root, stem or leaf which is used for propagation.
Factors are taken into consideration for successful propagation such as:
Sometimes the stem cuttings are treated with a rooting hormone (IBA, IAA or NAA) for the proper development of adventitious roots.
Examples: Sugar cane, Rose, Croton, Tapioca, China rose (Stem cutting) Lemon, Tamarind (Root Cutting), Sansevieria (Leaf-cutting).
The favourable time for cutting is the Rainy season.
(ii) Grafting: It is the most common method of vegetative propagation described by ancient gardeners long before the science of horticulture became established. In this method, parts of two plants are joined in such a way that they grow as one plant.
Grafting is done between two closely related dicotyledonous plants having vascular cambium. The rooted supported portion of one plant called Stock is joined with a twig of another plant called Scion. Generally, the rootstock belongs to wild variety which is resistant to disease & pest.GraftingThe scion is derived from the plant possessing better characters. In grafting, the stock and scion cuts are marked in such an oblique manner so that they fix with each other. This joint covered with clay or a layer of wax. Within a few days, tissues of stock and scion combine together to form a new plant.
Example: Grafted Mango, Roses, orange, Seedless Grapes and Guava, Apple, Pear.
The favourable time for grafting is the Spring season.
Different types of Grafting are:
(a) Tongue Whip-grafting
(b) Wedge-grafting
(c) Crown grafting
(d) Side grafting
(e) Approaching grafting
Bud Grafting: This method is similar to grafting except that scion in this case consists of a bud along with some portion of bark having intact cambium.
Generally, bud grafting is done during the rainy season
Examples: Roses, Peach.
(iii) Layering: This method is used in those plants which are having flexible long branches. In this method, roots are artificially induced on the stem branches before they are detached from the parent plants for propagation.
There are two common types of layerings:Types of Layering
(a) Mound/Ground Layering: This method is only utilized in herbaceous plants. In this method, the lower branch of the stem is bent down and partially defoliated and injury is made on the defoliated part. It is covered by a thin layer of moist soil in such a way that the growing tip of the branch remains above the soil surface. After a few days, the pegged portion develops adventitious roots. Then rooted branch cut and separated from the parent and grown into a new plant.
Example: Jasmine, strawberry, Raspberry etc.
(b) Air Layering or Gootee: This method is commonly employed in the case of shrubs and trees which do not possess branches near the ground. In this method, a ring of bark is removed (girdled) from the aerial branch. This girdled portion is covered with moist grafting clay (2parts clay + 1 part cow dung + some pieces of hay + cotton + water) and wrapped with a polythene sheet. This wrapped portion of the branch is called Gootee. Inside the gootee, roots developed within a period of a or two month(s).
Examples: Litchi, Pomegranate, Orange, Lemon, Bougainvillea, Guava etc.
➢ Merits of Vegetative Propagation
➢ Demerits of Vegetative Propagation
➢ Significance Of Vegetative Propagation
In flowering plants, there are two main types of Non-recurrent Apomixis:
(i) Parthenogenesis: In this process, the haploid egg cell of the female gametophyte is responsible to form a haploid embryo without fertilization.
(ii) Apogamy: In this process, any haploid cell of female gametophyte except egg cell is responsible to form a haploid embryo without fertilization.
Parthenogenesis and Apogamy both are not included in agamospermy.
If both gametophyte and sporophyte are diploid in parthenogenesis and apogamy then it is called diploid parthenogenesis and diploid apogamy.
Note: In Lilium all three types of polyembryony are present. (Adventive embryony is also example of polyembryony in which the additional number of embryos are formed from Nucleus or integuments).
Note:
- P.Maheshwari established: Research centre of Angiosperm Embryology at Delhi University.
- Book published by Maheshwari: An Introduction to the Embryology of Angiosperms.
Table: Differences Between Asexual and Sexual Reproduction
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1. What is asexual reproduction in plants? |
2. What are some common methods of asexual reproduction in plants? |
3. Why do plants use asexual reproduction? |
4. Are there any disadvantages of asexual reproduction in plants? |
5. Can a plant switch from asexual to sexual reproduction? |
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