- A sexual reproduction does not involve fusion of male and female gametes.
- New plants may develop from vegetative parts of the plant (vegetative reproduction) or may arise from embryos that develop without fertilization (apomixis).
1. Vegetative Reproduction:
- In nature, a new plant develops from a portion of the plant body.
- This may occur through modified underground and sub-aerial stems, and through bulbils.
2. Underground Stems:
- The underground modifications of stem generally serve as storage organs and contain many buds.
- These buds develop into shoots and produce plants after rooting. Examples of such modifications are given below.
Bulb: Onion, Garlic
Rhizome: Ginger, turmeric
Corm: Bunda, arwi
3. Sub-aerial Stems:
- These modifications include runner, stolon, sucker etc.
- Sub-aerial stems are used for the propagation of mint, date palm etc.
- Bulbils are modified flowers that develop into plants directly without formation of seeds.
- These are vegetative bodies; their development does not involve fertilization and seed formation.
- The lower flowers in the inflorescence of garlic naturally develop into bulbils.
5. Artificial Vegetative Reproduction:
- Stem cuttings are commercially used for the propagation of sugarcane, grapes, roses, etc.
- Layering, budding, grafting and gootee are in common use for the propagation of fruit trees and ornamental shrubs.
Significance of Vegetative Reproduction
- A desirable plant may be used as a variety directly regardless of whether it is homozygous or heterozygous.
- Further, mutant buds, branches or seedlings, if desirable, can be multiplied and directly used as varieties.
- In apomixis, seeds are formed but the embryos develop without fertilization.
- In apomictic species, sexual reproduction is either suppressed or absent.
- When sexual reproduction does occur, the apomixis is termed as facultative.
- But when sexual reproduction is absent, it is referred to as obligate.
- The embryo develops from embryo sac without pollination. It is of two types:
a) Gonial parthenogenesis – embryos develop from egg cell.
b) Somatic parthenogenesis – embryos develop from any cell of the embryo sac other than the egg cell.
- In apogamy, synergids or antipodal cells develop into an embryo.
- Like parthenogenesis, apogamy may be haploid or diploid depending upon the haploid or diploid state of the embryo sac.
- Diploid apogamy occurs in Antennaria, Alchemilla, Allium and many other plant species.
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