Topic is Asexual reproduction in plant ,in Detail with proper diagram and example.
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3. ASEXUAL REPRODUCTION
It is a mode of reproduction/multiplication in which new individuals develops from a
single parent.
Features of asexual reproduction:
1. As there is involvement of only one parent so it is uniparental.
2. It can occur with or without gamete formation but gametic fusion is absent.
3. The individuals produced are exact copies of each other and their parents because the
new organisms produced inherit all of its chromosome from one parent. Moreover, it
involve only mitotic division. Such a group of morphologically and genetically similar
individual is called clone.
4. It can occur through unspecialised or specialised parts of parent.
5. Higher plant also exhibit this type of reproduction where it is known as Vegetative
reproduction.
6. It is a simple and quick method of reproduction.
4. LET US DISCUSS DIFFERENT WAYS OF ASEXUAL
REPRODUCTION:
Binary fission
Budding
Sporulation
Fragmentation
Vegetative reproduction/propagation
5. 1. BINARY FISSION
Occurrence: It occurs in many single celled organisms belonging to kingdom
Monera (Bacteria), and Prostista (Amoeba and Paramecium).
Mechanisms : In this process, the parent organisms divides into two halves, each
half forming an independent daughter organism. It means, the parent body as a
whole forms reproductive unit and the parent continues living as two daughter
individuals. Thus, here cell division itself is a mode of reproduction.
It involves amitosis in bacteria and mitotic division of nucleus in yeast and amoeba
i.e., karyokinesis followed by division of cytoplasm i.e., cytokinesis resulting in the
formation of daughter cells.
Depending upon the plane of division, binary fission is of the following types
a) Simple Binary Fission(Irregular Binary fission):- Division can occur through any plane
e.g., Amoeba.
b) Longitudinal Binary Fission: The plane of fission passes along the longitudinal axis
of the organism e.g., Euglena
c) Transverse Binary Fission : The plane of this division runs along the transverse axis
of the individual e.g., Bacteria, Paramecium, Diatoms.
6. 2. BUDDING.
• Occurrence: Occurs in single celled organisms like yeast.
• Mechanism : In this process unicellular structure develops an outgrowth (bud) on one side.
Daughter nuclei produced through karyokinesis shifts into the bud. The bud grows, constricts at the
base and separates. So bud remains attached initially to the parent cells which eventually separates
and mature into new organisms (cells).
• Unlike binary fission, cytoplasmic division is unequal and parental cell exists.
7. 3. SPORULATION
o occurrence : These are formed by members of the kingdom fungi and simple plants such as
algae.
oType : The most commonly produced spores are zoospores and conidia.
o Zoospores : These are microscopic motile spores that move by means of flagella formed
under favourable condition. They are mot common asexual structure formed in algae.
o In unicellular green alga, Chlamydomonas zoospores is pyramid shaped, anteriorly
flagellated, resembling parents cells.
o During zoospores formation parents cells starts behaving like sporangia.
8. Conidia : These are non-motile spores produced by special hyphal branches called
conidiophores.
These are most common asexual spores produced by fungi. In Penicillium conidiophores may
shows branching and over these branches there is formation of flask shape structure called
sterigmata (phialides). Each sterigmata produces/cuts a chain of conidia.
Fig. : Asexual structure :Zoospores
of Chlamydomonas.
Fig. : Asexual structure : Conidia of
Penicillium.
9. 4. FRAGMENTATION.
Fragmentation is a form of asexual reproduction where an organisms spells into fragments.
Each of these fragments develops into mature fully grown individual followed by mitosis. It
occurs in some algae (Spirogyra), fungi and Hydra, etc.
10. 5. VEGETATIVE REPRODCUTION/PROPAGATION.
•It is a method of multiplication in which a somatic part of the plants detaches from the
body of the mother and develops into a new independent plant under suitable
environmental conditions.
•The detachable somatic part involved in vegetative propagation is called vegetative
propagule.
•There are two types of vegetative reproduction :
A. Natural methods of vegetative reproduction :
B. Artificial or Horticultural method of vegetative reproduction.
A. Natural Methods of Vegetative Reprodcution :
1. Stem :
i. Underground stem
ii. Subaerial stem
iii. Aerial stem
iv. Bulbils
2. Leaves
3. Roots
11. 1. STEMS.
i. Underground stem:
(a) Tuber: it is a terminal portion of an underground stem branch which is swollen on account of
accumulation of food. They possess buds over their nodes or eyes. This buds sprouts to produce
new plantlets, when a stem tuber or a part of it having an eye is placed in the soil. E.g., Potato
Fig. : Eyes of Potato
(b) Rhizome: It is the main underground perennial stem. Buds present on the node take part for
formation of new aerial shoot during favourable season of growth. E.g., Banana, Ginger.
12. (c) Bulb: it is an underground unbranched reduced disc shaped stem. Termininal bud is
surrounded by several leaves e.g., Onion, Garlic.
Fig. : Bulb of Onion
(ii) Subaerial stem :
(a) Offset : Short horizontal branch producing a cluster of leaves above and the cluster of roots
below is called offset. It occurs in some aquatic plants. Breaking of offsets helps in propagation e.g.,
Eichhornia (water hyacinth), Pisita (water Lettuce).
Fig. : Offset of water hyacinth
13. (b) Sucker : it arises by axillary bud of underground part of stem e.g., Chrysanthemum, Pineapple.
(c) Runner : It is elongated, prostrate, sub-aerial branch with long internodes and roots at nodes.
E.g., Grasses.
Fig. : Sucker in Chrysanthemum Fig. : Runner of grass
(iii) Aerial shoots : Each segment of stem having at lest one node can form a new plant. E.g., Sugarcane,
Opuntia.
14. (iv) Bulbils : These are large size fleshy buds which are specialised for vegetative reproduction. For this
bulbil must fall from the plant and reach the soil. They can be present at variable positions on
plants. In Agave bulbils are modified floral buds that develop on the floral axis.
e.g., Agave (century plant), oxalis, Ananas, Dioscorea, lily.
2. Leaves : Leaves of several plants having adventitious buds help in vegetative reproduction. In
Bryophyllum adventitious buds arise from the notches present at margins of leaves. E.g., Adiantum
(walking fern), Begonia, kalanchoe.
Fig. : Bulbil of Agave Fig. : Bryophyllum.
3. Roots : It was discussed that one of the prerequisites for vegetative reproduction is presence of
buds. Though bud is mainly the feature of stem but in some plants roots may also bear buds. These
adventitious buds sprout to form new plants e.g., Dahlia.
15. B. ARTIFICIAL METHOD OF VEGETATIVE REPRODCUTION.
1. Cuttings :
i) Stem Cuttings: it is a common artificial method of plant propagation. 20-30cm long pieces of one
year old stems are cut and their lower ends are dipped in dilute auxin for several minutes before
planting in the soil. The lower ends develops adventitious roots. Buds present over the exposed
parts sprout and form the shoot system.
e.g., Rose, Duranta, Cirtus, Clerodendron, Thea, Bougainvillea, Croton and China Rose
ii) Leaf cuttings: Snake plant (Sansevieria) can be propagated by leaf cuttings. Leaves are cut
transversely into two or three parts and planted in vertical position in the soil. For successful leaf
cutting, besides induction of rooting, formation of adventitious buds is also important.
iii) Root cuttings: They are long pieces of roots which are used to artificially propagate new plants.
Ability to form adventitious roots and adventitious buds are pre-requisites.
Roots are used in propagation of Lemon, Tamarind, Blackberry and Raspberry.
Fig. : Stem cutting.
16. 2. Layering :
•It is a type of rooting-cutting method in which adventitious roots are induced to develop on a soft stem
while it is still attached to the plant.
•It is carried out on one year old basal shoot branches commonly during early spring or early rainy season
Layering is of following types
a) Tip layering : It induces root formation and later growth of shoot tip e.g., Blackberry, Raspberry.
b) Trench Layering : It develops a number of vertical shoots e.g., Walnut, Mulberry.
c) Gootee (Air layering) : it is an ancient horticultural technique for propagation of tropical and
subtropical trees and shrub where soft branches do not occur near the soil.
METHOD : During early monsoon rains, 3-5 cm long ring of bark is removed form the basal region of
a healthy and woody branch. It is covered by a thick plaster of grafting clay. Grafting clay is made of 1
part cow dung, 1 part finely cut hay or moss and two parts clay. To its added water and a small
quantity of root promoting hormones like IAA, IBA or NAA. It is then wrapped in polythene. After 2-
3months roots appear. The shoot is now cut below the covered part and used for planting.
E.g., Litchi, Pomegranate.
Fig. : Tip layering Fig. : Trench layering
17. 3. Grafting:
• Grafting is a technique of connecting two parts, usually a root system and a shoot system of two
different plants in such a way that they unite and later develop as a composite plant.
• It is used only in cambium containing eustelic plants.
• A small shoot of plant with superior traits is employed. It is called graft or scion. The root system of
the other plant is allowed to remain intact. It is called stock (Under stock). E.g., Mango, Apple,
Citrus.
Fig. : Grafting
Various types of grafting
a) Tongue (slice or whip grafting) : Oblique sloping cut or notch is given to both stock and scion.
b) Wedge Grafting: V shaped notch.
18. c) Crown Grafting: Wedge shaped
d) Approach Grafting : Two independently growing plants are brought together.
e) Bud Grafting: Scion is a bud with a small piece of bark and cambium. Stock is given a T
shaped cut. Bark is lifted to expose cambium. Bud is inserted and the bark is allowed to
come back to its original position. Only the bud is exposed. The joint is treated with
grafting wax and is bandaged. But sprouts after 3-5 weeks. Bud grafting is commonly
practiced in apple, peach and rose
Fig. : Crown grafting Fig. : Approach Grafting.
Fig. : Bud Grafting.
4. Micropropagtion : Micropropagation is the raising of new plants from a small plant tissue with the
help of tissue culture technique. Tissue Culture is the technique of maintaining and growing cells,
tissues, etc. and their differentiation on artificial medium under aseptic condition inside suitable
containers.
