- Reproduction is defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself.
- The offspring grow, mature and in turn produce new offspring. Thus, there is a cycle of birth, growth and death. Reproduction enables the continuity of the species, generation after generation.
Types of Reproduction
- Asexual Reproduction: When offspring is produced by a single parent with or without the involvement of gamete formation, the reproduction is asexual.
- Sexual Reproduction: When two parents (opposite sex) participate in the reproductive process and also involve fusion of male and female gametes, it is called sexual reproduction.
Characteristics of Asexual Reproduction
- In this method, a single individual (parent) is capable of producing offspring. A
- As a result, the offspring that are produced are not only identical to one another but are also exact copies of their parent.
- These offspring are genetically and morphologically identical to parents
- The term clone is used to describe such morphologically and genetically similar individuals.
- Usually followed by organisms with relatively simpler organizations
Types of Asexual Reproduction:
- In Protists and Monerans, the organism or the parent cell divides into two to give rise to new individuals.
- Thus, in these organisms cell division is itself a mode of reproduction. Many single-celled organisms reproduce by binary fission, where a cell divides into two halves and each rapidly grows into an adult
- e.g., reproduction in Amoeba, Paramecium, Viruses.
- In yeast, the division is unequal and small buds are produced that remain attached initially to the parent cell which, eventually gets separated and mature into new yeast organisms (cells). e.g
- e.g. reproduction in Yeast and hydra
- Members of the Kingdom Fungi and simple plants such as algae reproduce through special asexual reproductive structures.
- The most common of these structures are zoospores that usually are microscopic motile structures.
- Other common asexual reproductive structures are conidia (Penicillium), buds (Hydra) and gemmules (sponge).In fungi and algae, specialized asexual reproductive units are formed.
Natural Methods of Vegetative Propagation (Asexual reproduction):
- Vegetative Propagation is an asexual method of reproduction in plants.
- In plants, the units of vegetative propagation such as runner, rhizome, sucker, tuber, offset, bulb are all capable of giving rise to new offspring. These structures are called vegetative propagules.
- Since the formation of these structures does not involve two parents, the process involved is asexual.
- Tuberous Roots:
- The roots of such plants have adventitious buds on their surface which sprout under favourable conditions to produce leafy shoots.
- In Commercial Production these sprouts are separated and planted. Thus many plants can be obtained from a single root.
- e.g. Sweet potato, Asparagus (Shatavari), Dahlia
- Stem Tubers:
- A stem tuber has many notches called ‘eyes’ on their surface.
- Each eye actually a node and consists of one or more small axillary buds and reduced scale leaves.
- After dormancy period the eyes which sprout under favourable conditions to produce leafy shoots.
- In Commercial Production the tuber is cut into pieces, such that each piece has at least one eye. Then they are grown separately. Thus many plants can be obtained from a single tuber.
- e.g. Potato, Ginger
- Runner develops from the lower axillary bud of stem and thin elongated cylindrical wire-like structure with long internodes.
- It creeps on the ground and becomes rooted at the nodes. Shoots are produced from upper sides of nodes.
- After getting detached from a parent, such shoots grow as an independent plant.
- e.g. Cynodon (doobgrass), Fragaria (strawberry), Oxalis
- In bryophyllum, the leaf is succulent with crenate or notched margins.
- Adventitious buds called epiphyllous buds or foliar buds are formed at notches at the tip of lateral veins.
- These buds sprout and form leafy shoots and adventitious roots.
- When such sprout falls on wet soil, they develop into independent plants.
- e.g. Bryophyllum, Kalanchoe, Begonia
- Hazard due to Water Hyacinth (Terror of Bengal)
- One of the most invasive weeds
- Grows wherever there is standing water
- Drains oxygen from water- leads to the death of fishes.
- Introduced in India because of its pretty flowers & shape of leaves
- Vegetative propagation occurs at a phenomenal rate
Artificial Methods of Vegetative Propagation (Asexual reproduction):
- In this method, a branch of plant part (stem, root or leaves) is cut with a node (primary meristem) on it. This piece of a branch is termed a cutting.
- This cutting is buried in the soil.
- The cutting is watered continuously.
- This method is the cheapest and convenient method of vegetative propagation.
- In this method, the parts of two different plants are joined together in such a way that they unite and continue their growth as one plant.
- The plant rooted to the soil and on which the part of the other plant is inserted is called a stock.
- The other plant which is inserted on the stock is called Scion or graft.
- Budding is a special case of grafting in which a single bid with a small part of a bark and living tissue is grafted on another plant.
The significance of Vegetative Propagation:
- It is easy and cheaper method of multiplication.
- The plants like banana, pineapple and grapes which do not produce viable seeds can be propagated by vegetative propagation only.
- In this method, genetically similar plants are formed.
- The yield can be increased by grafting high-yield variety on less yielding variety but which is adapted to the region.
- This is a rapid method of propagation particularly for the plants having a long dormancy period.
- It can be used to get clones of rare plants.