Somatic hybridization
- The technique of hybrid production through the fusion of protoplast from different genetic backgrounds takes place is known as somatic hybridization or parasexual hybridization or protoplast fusion.
- Significance for the improvement of vegetatively propagated plants such as banana, cassava, potato, sweet potato, and sugarcane.
- It includes:
a) Isolation
b) Fusion of protoplasm
c) Selection
d) Culture of hybrid cells
Procedure
- Collection of explants
- Protoplast isolation
- Protoplast fusion
- Selection of Hybrid cells
- culture of Hybrid cells
- Regeneration of plants from hybrid tissue
- Characterization of Hybrid and cybrid plants
Selection of hybrid cells
- The Protoplast suspension recovered after the treatment with fusion inducing agent fusogen) consists of following cell types
a) unfused protoplasts of the two species / strains
b) Homokaryons (two or more protoplasts of same species)
c) Heterokaryons (hybrid protoplasts)
Culture of hybrid cells
- The isolated hybrid cells may be cultured on a suitable medium and can be induced to develop a new cell wall, divide and regenerate either through embryoid formation (or) production of calli.
Regeneration of plants from hybrid tissue
- Once the hybrid calli (or) embryoids are obtained, the plants are induced to regenerate from them since this is a pre requisite for exploitation in crop improvement.
- Further, the hybrid plants must be at least partially fertile, in addition to having some useful property to be of any use in breeding schemes.
- The hybrid plants thus obtained through somatic hybridization may be
a) Symmetric hybrids
b) Asymmetric hybrids
c) Cybrids
Cytoplasmic hybrid/Cybrid
- Defined as cell (or) plant which is produced by fusion of protoplast of one parent and cytoplast of another parent.
- Cybrid possess nuclear genes from only one parent and cytoplasm from both parents.
- In cultures cybrids may be produced by one of the following means.
a) fusion of a normal protoplast of one species with an enucleated protoplast (cytoplast) (or) a protoplast having an inactivated nucleus of other species
b) Elimination of nucleus of one species from a normal heterkokaryon or gradual elimination of chromosome of one species from a hybrid cell during the subsequent mitotic divisions.
c) The objective of cybrid production is to be combine cytoplasmic genes of one species with nuclear and cytoplasm of genes of another species
Applications of somatic hybridization
a) Production of novel interspecific and intergeneric crosses between the plants that are difficult (or) impossible to hybridize conventionally. Eg: Potato x tomato = pomato.
b) Transfer of desirable genes for disease resistance
c) Transfer of desirable genes for Abiotic stress resistance. E.g., Atrazine (resistance) has been transferred from wild species of tomato lycopersicon peruvianum into cultivated species (Lycopersicon esculentum)
d) Transfer of desirable genes for quality characters
e) Transfer of cytoplasmic male sterility
f) Overcoming sub in compatible barriers